Digital PDFs

DEC-11-OIODA-B-D

May 1978

94 pages

Original

4.2MB

Document:	IAS/RSX-11 ODT Reference Manual
Order Number:	DEC-11-OIODA-B-D
Revision:	0
Pages:	94
Original Filename:	http://bitsavers.org/pdf/dec/pdp11/rsx11m_s/RSX11M_V3.2_Jun79/3A_ProgramDevelopment/DEC-11-OIODA-B-D_RSX_ODT_Ref_197705.pdf

OCR Text

IAS/RSX-11
ODT Reference Manual
Order No. DEC-11'-0IODA-B-D

RSX-11 M Versions 3.0 and 3.1
RSX-11 D Version 6.2
IAS Versions 1.1, 2.0 and 3.0

To order additional copies of this document:, contact the Software Distribution
Center, Digital Equrpment Corporation, Maynard, Massachusetts 01754

digital equipment corporation · maynard, massachusetts

First Printing, December 1975
Revised:
May 1977

The information in this document is subject to change without notice
and should not be construed as a commitment by Digital Equipment
Corporation. Digital Equipment Corporation assumes no responsibility
for any errors that may appear in this document.
The software described in this document is furnished under a license
and may only be used or copied in accordance with the terms of such
license.
No responsibility is assumed for the use or reliability of software on
equipment that is not supplied by DIGITAL or its affiliated companies.

<£) 1975, 1977, 1978 by Digital Equipment Corporation

The postage-prepaid READER'S COMMENTS form on the last page of this
document requests the user's critical evaluation to assist us in preparing future documentation.
The following are trademarks of Digital Equipment Corporation:

DIGITAL
DEC
PDP
DEC US
UNIBUS
COMPUTER LABS
CO MT EX
DDT
DECCOMM
ASSIST-11
VAX
DECnet

DECsystem-lo
DECtape
DIBOL
EDUSYSTEM
FLIP CHIP
FOCAL
INDAC
LAB-8
DECSYSTEM-20
RTS-8
VMS
IAS

10/80-14

MAS SB US
OMNIBUS
OS/8
PHA
RSTS
RSX
TYPESET-8
TYPESET-11
TMS-11
ITPS-10
SB!

TABLE OF CONTENTS
Page
vii

PREFACE
0.1
0.2
0.3

MANUAL OBJECTIVES AND READER ASSUMPTIONS
STRUCTURE OF THE DOCUMENT
ASSOCIATED DOCUMENTS

vii
vii
viii

INTRODUCTION

1-1

1.1
1. 2
1. 2 .1
1. 2. 2
1. 2. 3
1. 3
1. 3.1
1. 3. 2

ODT INTERNAL ORGANIZATION
OPERATIONAL DESCRIPTION
Linking ODT into the User Program
'user Task Breakpoints
Relocation Registers
EXPRESSING ODT COMMANDS AND FUNCTIONS
Forms of Address Expressions
Examples of Address Expressions

1-1
1-2
1-3
1-3
1-4
1-4
1-5
1-6

CHAPTER

ODT CHARACTERS AND SYMBOLS

2-1

CHAPTER

ODT COMMAND SEQUENCES AND FUNCTIONS

3-1

3.1
3.2

PRINTING TASK ADDRESSES
COMMANDS FOR OPENING, CHANGING, AND
CLOSING LOCATIONS
Close Current Location: <CR> or k<CR>
Open Next Sequential Location: <LF> or
k<LF>
Open Word Location: I or a/
Open Byte Location: \ or a\
Open Preceding Location:
or kA
Open PC-Relative Location:
or k
Open Absolute Location:
@ or k@
Open Relative Branch Offset Location:
> or k>
Return to Interrupted Sequence:
< or k<
ACCESSING USER PROGRAM GENERAL REGISTERS: $n
ACCESSING SPECIAL ODT INTERNAL REGISTERS:
$x or $nx
TASK BREAKPOINT COMMANDS:
a;B, a;nB, B, or
nB
PROGRAM EXECUTION COMMANDS:
G or aG and P
or kP
SINGLE-INSTRUCTION MODE COMMANDS:
S or nS
SEARCH OPERATIONS
Word/Byte Search Commands: W, kW, m;W,
or m;kW
Not This Word/Byte Search Commands: N,
kN, rn;N, or m;kN
·Effective Address Search Commands:
E,
kE, m;E, or m;kE
FILL COMMANDS:
F or kF
OFFSET CALCULATION COMMANDS:
aO or a;kO
RELOCATION REGISTER COMMANDS:
a;nR,
a;R, nR, or R
REI,OCATION CALCULATOR COMMANDS:
a; nK, nK,
or K
LISTING COMMANDS: L, kL, a;L, a;kL, or
n; a.; kL
REPRINTING OPEN LOCATIONS

3-1

CHAPTER

3.2.l

3.2.2
3.2.3
3.2.4
3.2.5
3.2.6

3.2.7
3.2.8

3.2.9
3.3
3.4
3.5
3.6

3.7
3.8
3.8.l
3.8.2

3.8.3
3.9
3 .10
3.11
3.12

3.13
3.14

iii

3-2
3-2
3-2
3-2
3-4
3-5
3-6
-3-6
3-7
3-8
3-9
3-10
3-15
3-17
3-19
3-20
3-21

3-23
3-23
3-24
3-25
3-27
3-29

3-29
3-33

CONTENTS (Cont.)
Page
3.14.1
3.14.2
3.14.3
3.14.4

CHAPTER

3.15
3.16
3.16.l
3.16.2
3.16.3
3.16.4
3.17

Print Octal Byte Value: \
Print Byte Mode ASCII Character:
' or a'
11
Print Word Mode ASCII Characters:
or a"
Print Word Mode Radix-50 Characters:
% or a%
INTERPRETING EXPRESSION VALUES: k=
USING SPECIAL ARGUMENTS IN ODT COMMANDS
Current Location Indicator:
Constant Register Indicator: C
Quantity Register Indicator: Q
Radix-50 Operator:
*
REENTRY VECTOR REGISTER:
$X

3-36
3-36
3-37
3-37
3-37
3-38
3-39
3-40

OPERATING PROCEDURES

4-1

4.1
4.2
4.3
4.3.1
4.3.2
4.4
4.5

FILE TYPE OR EXTENSION VALUES
OUTPUT FILE SWITCH OR QUALIFIER OPTIONS
LINKING AND INITIATING ODT
RSX-11 Systems
IAS System
OTHER DEBUGGING AIDS
RETURNING CONTROL TO THE HOST SYSTEM

4-1
4-1
4-2
4-2
4-3
4-3
4-4

ERROR DETECTION

5-1

5.1
5.2

COMMAND INPUT ERRORS
TASK IMAGE ERROR CODES

5-1
5-2

TRACE DEBUGGING AID

6-1

6.1
6.2

INTRODUCTION
OPERATIONAL INFORMATION

6-1
6-2

PROCESSOR STATUS WORD

A-1

MODES (MEMORY MANAGEMENT OPTION)
PROCESSOR PRIORITY
TRAP -(T-BIT)
CONDITION CODES
TRAP PROCESSING

A-1
A-2
A-2
A-2
A-2

SEARCH ALGORITHMS

B-1

WORD/BYTE SEARCHES (W or N)
EFFECTIVE ADDRESS SEARCH (E)

B-1
B-1

APPENDIX A
A.l
A. 2
A. 3
A. 4
A. 5

APPENDIX B
B.l
B.2
INDEX

3-34
3-34
3-35

Index-1

FIGURES
Page
FIGURE

1-1
3-1
6-1
A-1

ODT Communications and Data Flow
ODT Listing Modes and Formats
Sample Trace Output
Format of Processor Status Word

1-2
3-32
6-2
A-1

TABLE

OF CONTENTS
Page
vii

PREFACE
0.1
0.2
0.3

MANUAL OBJECTIVES AND READER ASSUMPTIONS
STRUCTURE OF THE DOCUMENT
ASSOCIATED DOCUMENT$

vii
vii
viii

INTRODUCTION

1-1

1.1
1. 2
1. 2 .1
1. 2. 2
1. 2. 3
1. 3
1. 3.1
1. 3. 2

ODT INTERNAL ORGANIZATION
OPERATIONAL DESCRIPTION
Linking ODT into the User Program
User Task Breakpoints
Relocation Registers
EXPRESSING ODT COMMANDS AND FUNCTIONS
Forms of Address Expressions
Examples of Address Expressions

1-1
1-2
1-3
1-3
1-4
1-4
1-5
1-6

CHl\PTER

ODT CHARACTERS AND SYMBOLS

2-1

CHAPTER

ODT COMMAND SEQUENCES AND FUNCTIONS

3-1

3.1
3.2

PRINTING TASK ADDRESSES
COMMANDS FOR OPENING, CHANGING, AND
CLOSING LOCATIONS
Close Current Location: <CR> or k<CR>
Open Next Sequential Location: <LF> or
k<LF>
.
Open Word Location: I or a/
Open Byte Location: \ or a\
Open Preceding Location: A or kA
Open PC-Relative Location:
or k
Open Absolute Location: @ or k@
Open Relative Branch Offset Location:
> or k>
Return to Interrupted Sequence:
< or k<
ACCESSING USER PROGRAM GENERAL REGISTERS: $n
ACCESSING SPECIAL ODT INTERNAL REGISTERS:
$x or $nx
TASK BREAKPOINT COMMANDS:
a;B, a;nB, B, or
nB
PROGRAM EXECUTION COMMANDS: G or aG and P
or kP
SINGLE-INSTRUCTION MODE COMMANDS: S or nS
SEARCH OPERATIONS
Word/Byte Search Commands: W, kW, m;W,
or m;kW
Not This Word/Byte Search Commands: N,
kN, m;N, or m;kN
Effective Address Search Commands: E,
kE, m;E, or m;kE
FILL COMMANDS: F or kF
OFFSET CALCULATION COMMANDS:
ao or a;kO
RELOCATION REGISTER COMMANDS:
a;nR,
a;R, nR, or R
RELOCATION CALCULATOR COMMANDS:
a;nK, nK,
or K
LISTING COMMANDS: L, kL, a;L, a;kL, or
n;a;kL
REPRINTING OPEN LOCATIONS

3-1

CHAPTER

3.2.1
3.2.2
3.2.3
3.2.4
3.2.5
3.2.6
3.2.7
3.2.8
3.2.9
3.3
3.4
3.5
3.6
3.7
3.8
3.8.1
3.8.2
3.8.3
3.9
3 .10
3.11
3.12
3.13
3.14

iii

3-2
3-2
3-2
3-2
3-4
3-5
3-6
·3-6

3-7
3-8
3-9
3-10
3-15
3-17
3-19
3-20
3-21
3-23
3-23
3-24
3-25
3-27
3-29
3-29
3-33

CONTENTS (Cont.)
Page
3.14.l
3.14.2
3.14.3
3.14.4

CHAPTER

3.lS
3.16
3.16.l
3.16.2
3.16.3
3.16.4
3.17

Print Octal Byte Value: \
Print Byte Mode ASCII Character:
' or a'
Print Word Mode ASCII Characters:
" or a"
Print Word Mode Radix-SO Characters:
% or a%
INTERPRETING EXPRESSION VALUES: k=
USING SPECIAL ARGUMENTS IN ODT COMMANDS
Current Location Indicator:
Constant Register Indicator: C
Quantity Register Indicator: Q
Radix-SO Operator:
*
REENTRY VECTOR REGISTER:
$X

3-36
3-36
3-37
3-37
3-37
3-38
3-39
3-40

OPERATING PROCEDURES

4-1

4.1
4.2
4.3
4.3.l
4.3.2
4.4
4.S

FILE TYPE OR EXTENSION VALUES
OUTPUT FILE SWITCH OR QUALIFIER OPTIONS
LINKING AND INITIATING ODT
RSX-11 Systems
IAS System
OTHER DEBUGGING AIDS
RETURNING CONTROL TO THE HOST SYSTEM

4-1
4-1
4-2
4-2
4-3
4-3
4-4

ERROR DETECTION

S-1

S.l
S.2

COMMAND INPUT ERRORS
TASK IMAGE ERROR CODES

S-1
S-2

TRACE DEBUGGING AID

6-1

6.1
6.2

INTRODUCTION
OPERATIONAL INFORMATION

6-1
6-2

PROCESSOR STATUS WORD

A-1

MODES (MEMORY MANAGEMENT OPTION)
PROCESSOR PRIORITY
TRAP . (T-BIT)
CONDITION CODES
TRAP PROCESSING

A-1
A-2
A-2
A-2
A-2

SEARCH ALGORITHMS

B-1

WORD/BYTE SEARCHES (W or N)
EFFECTIVE ADDRESS SEARCH (E)

B-1
B-1

.APPENDIX A
A.l
A. 2
A. 3
A. 4
A. S

APPENDIX B
B.l
B.2
INDEX

3-34
3-34
3-35

Index-1

FIGURES
Page
FIGURE

1-1
3-1
6-1
A-1

ODT Communications and Data Flow
ODT Listing Modes and Formats
Sample Trace Output
Format of Processor Status Word

1-2
3-32
6-2
A-1

CONTENTS (Cont. )
TABLES
Page
TABLE

1-1
1-2
2-1
3-1
3-2
5-1

Common Elements of :Keyboard Sequences
Forms of Address Expressions
ODT Characters/Symbols
Internal Register Access/Modification
Commands
Legal Radix-SO Characters and Numeric
Equivalents
ODT Error Codes

1-4
1-5
2-2

3-11
3-40
5-2

1.-.................

1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ._ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ __

PREFACE

0.1

MANUAL OBJECTIVES AND READER ASSUMPTIONS

The intent of this manual is to enable its users to understand the
debugging techniques provided by ODT.
Readers are assumed to be
familiar with the information contained in:
1.

An appropriate PDP-11 Processor
/10, /35, /40, /45, or /70)

Handbook

(i.e.,

PDP-11/05,

IAS/RSX-11 MACR0-11 Reference Manual

An appropriate Task Builder Reference Manual (i.e., for
RSX-llD, or RSX-llM)

IAS,

It is also important for readers of this manual to have gained an
understanding of the terminal device providing the primary operator
interface to the PDP-11 processor.
For example, on some terminals an
up-arrow may be present instead of a circumflex, and a back-arrow
instead of an underline character.
In presenting ODT-11, a tutorial format has been adopted that includes
explanatory text following actual ODT-11 command sequences. Thus, the
flow of material throughout this manual is biased toward the user who
is encountering ODT-11 for
the first time. Also, those terms and
expressions having particular significance in describing the functions
and operations of ODT-11 are defined at appropriate points in the
manual.

0.2

STRUCTURE OF THE DOCUMENT

Chapter 1 briefly describes the features of ODT-11 and the functions
of the three major modules forming the program. Some of the important
operational aspects of ODT-11 are described, and the common notation
used for describing all ODT-11 command sequences is defined.
Chapter 2 presents the characters and symbols that form the vocabulary
of ODT-11/user communications. The significance of these characters
and symbols in a functional and operational sense is defined
in this
chapter.
Chapter 3 describes the composition and function of all the ODT-11
command sequences available to the user for debugging purposes.
It is
in this chapter .that the explanatory text following the command
sequence examples has been employed.

vii

Chapter 4 presents the operating procedures for linking and
ODT-11 with user programs.

executing

Chapter 5 describes ODT-ll's response to errors in the keyboard
command
sequences
and
lists
the error codes resulting from
hardware-detected errors during user program execution.
Chapter 6 describes the Trace
complements the functions of ODT.

program,

debugging

aid

that

Finally, Appendix A and Appendix B present details of interest in the
Processor Status word and the ODT-11 search algorithms, respectively.

0.3

ASSOCIATED DOCUMENTS

Other manuals closely allied to the purposes of this document are
described
briefly
in
the
IAS,
RSX-llD,
or RSX-llM/RSX-llS
Documentation Directory.
The appropriate Documentation Directory
defines the intended readership of each manual in the set for the host
operating system, and provides a brief synopsis of each manual's
contents.

viii

CHAPTER 1
INTRODUCTION

ODT-11 operating under the Executive of the host system, aids the user
in debugging assembled and linked object programs. Through keyboard
interaction with ODT, the user can:
Print the contents of any location in the object
examination or alteration.
Run all or any portion of an
breakpoint feature.

object

Search the object program for words
pattern.

program
having

Search the object program for instructions
specified address.

program

using
a

the

ODT

specified

bit

that

reference

Calculate offsets for PC-relative references
displacements within the object program.
Fill a specified block of words or
value.

bytes

with

for

and
a

branch

designated

List a specified block of words or bytes for examination.

1.1

ODT INTERNAL ORGANIZATION

Internally, ODT is modularized
provide three major functions:
1.

Command decoding

Command execution

Utility routines

into

independent

subroutines

that

The ODT command decoder routines interpret keyboard commands, check
for
command errors, save input parameters for use in command
execution, and transfer control to the appropriate ODT command
execution routines.
The command execution routines take the input parameters saved by the
command decoder routines and call the ODT utility routines to execute
the specified command. The command execution routines then exit to
the object program or return control to the command decoder routines
to await further keyboard input.

1-1

INTRODUCTION
The utility routines, used by both the command decoder and command
execution routines, save and restore the contents of registers and
program locations and
perform
required
keyboard
input/output
operations.
The flow of control and data between the CDT
object program is illustrated in Figure 1-1.

routines

and

the

user

MANUAL ENTRY

COMMAND
DECODER

BREAKPOINT
HANDLER

PROGRAM
EXAMINATION &
MODI Fl CATION
COMMANDS

PROGRAM
ACTION
COMMANDS

INTERNAL
TABLE
MANIPULATION
COMMANDS

------------------~
USER
PROGRAM

r---1

I
I

ODT
INTERNAL
TABLES

UTILITY
ROUTINES
(1/0, ETC.)

User Environment
Legend

ODT
- - - - - - Flow of Control
- - - - - - - - - - Flow of Data

Figure 1-1
ODT Communications and Data Flow

1.2

OPERATIONAL DESCRIPTION

The following paragraphs describe the essential operational aspects of
ODT in the user environment.

1-2

INTRODUC~rION

1.2.1

Linking ODT into the User Program

At task-build time, ODT is linked to the user object program by the
Task Builder, thus incorporating ODT into the overall task image.
If
the task image is overlaid, ODT will be linked into the
root segment
of the
task so that it will always be available for debugging use.
The term "task" or "task
image,"
as used throughout this manual,
refers to that body of code resulting from Task Builder processing
which can be loaded and executed directly.
Once incorporated into the
task image,
ODT's usefulness as a debugging
tool stems from its
ability to establish selected breakpoints anywhere
in the current
memory-resident portion of a user program.
ODT runs as part o:E the user task and does not affect overall
system
operation.
Furthermore,
it is executed with the same privileges and
at the same priority level
as the
task to which
it
is linked.
Multiple tasks, each linked to its own copy of ODT, can be debugged at
the same time, provided that sufficient memory and a
terminal are
available for each active task.

1.2.2

User Task Breakpoints

Breakpoints are user-selected locations at which execution
is to be
halted temporarily to permit interaction with the user task and ODT.
Thus, ODT functions effectively as a monitor for the user task during
a debugging session.
When the~ser
task
is executed under ODT control,
the original
contents of a
breakpoint location are saved by ODT for
later
restoration.
At the same time,
ODT places a
Breakpoint
Trap
instruction
(octal op-code 000003) in the breakpoint location.
Up to
eight such breakpoint locations can be established in the user task at
any given time.
Later, during the active debugging session, program
execution proceeds normally until a breakpoint location
is reached.
The Breakpoint Trap
(BPT)
instruction
is then executed, causing
control to be transferred to ODT.
ODT then restores the original user
instruction to
the breakpoint location and awaits any valid command
for a wide range of debugging operations.
Breakpoints must be set only in the
first word of an
instruction,
since the BPT
instruction must be executed to cause the trap action
and the yielding of control
to ODT.
After
the desired debugging
operations associated with the current breakpoint have been performed,
the user issues an appropriate ODT command to continue execution.
ODT
then resets all breakpoints to the BPT instruction (including the
current breakpoint), and continues task execution.
The assembly listing of the program under examination should be at the
terminal
for
reference
during
the debugging
session.
Minor
corrections to the program may be made on-line.
The program can then
be run under ODT control to verify any changes made.
Major program
modifications, however, are more complex and should be noted on the
assembly listing.
In either case, all necessary changes should be
incorporated
into the
task
image through
a
subsequent
edit,
reassembly, and relinking of the program.

1-3

INTRODUCTION
1.2.3

Relocation Registers

When MACH0-11 produces a relocatable object module, the base address
of each program section in the module is relocatable 000000. The
addresses of all program locations, as shown in the assembly listing,
are therefore indicated relative to this base address. After the
module is linked by the Task Builder to physical memory locations (for
an unmapped system) or to virtual memory locations (for a mapped
system), many values within the resulting object module will be biased
by a constant whose value is the actual absolute base address of the
object module after it has been relocated. This constant is called
the relocation bias for the object module. Since a task may contain
several relocated object modules (each with its own relocation bias),
these biases must be continually subtracted from absolute addresses
during debugging operations in order to associate relocated code with
the assembly listing. ODT provides an automatic relocation facility
for calculating the relocation bias of each object module in a
relocatable program.
This facility is provided through eight relocation registers, numbered
0 through 7, each of which may be set by the user to the relocation
bias of an object module at any given time during
debugging
operations.

""·

The relocation bias of each program section in the task image is
obtained by consulting the memory map produced by the Task Builder.
Once set, a relocation register is used by ODT to relate the assembly
listing to the relocated code.
For a more detailed description of the linking and relocation process,
refer to the Task Builder Reference Manual for the host operating
system.

1.3

EXPRESSING ODT COMMANDS AND FUNCTIONS

In debugging operations, many ODT commands and functions are expressed
in keyboard sequences involving two or more characters. Such keyboard
sequences, having several
common
elements,
appear
frequently
throughout this manual.
For consistency, the notation in Table 1-1
has been adopted to facilitate the expression and understanding of all
user keyboard interaction with ODT. This notation is particularly
significant in Chapters 2 and 3.
Table 1-1
Common Elements of Keyboard Sequences
Symbol

Meaning

Represents an argument that is used
address of a task image location.

define

the

Represents an octal integer in the range 0 through 7.

Represents an octal value up to six digits in length,
with a maximum value of 177777(8), or an expression
which reduces to such a value.
If more than six
digits are specified, ODT takes oniy the last six
digits, truncated to the low-order 16 bits. The octal
value may be preceded by a minus sign, in which case,
the 2's complement of the value is taken by ODT.
1-4

.............................................................______________________________________________
,

INTRODUCTION
The following examples illustrate how octal values (k) are interpreted
by ODT:
Symbol k
(Octal Value Typed)

1.3.l

ODT
Interpretation

000001

-1

177777 (2 's complement)

400

000400

-1 77730

000050 (2's complement)

1234567

034567 (Truncated to low-order 16 bits)

Forms of Address Expressions

An address expression is always evaluated by ODT as a 16-bit (six
octal digit) value. This -address expression is represented throughout
this manual with the symbol a. An address expression may be typed in
any one of three general forms, as described in Table 1-2.
Table 1-2
Forms of Address Expressions
Form of
Expression

Format of
Expression

Resulting Address
Expression (a)

The value of
value of k.

Type 2

n,k

'1 he value of (a) is the value of k,
plus the contents of relocation
register n, where n designates any
of
one
ODT's eight relocation
registers. In this form, k is a
relocatable
address.
If n is
ODT
types
a
greater than 7'
(?)
character,
question
mark
ignores the current command, types
(_)
prompting
the
underline
valid
character, and awaits
a
command. ODT recognizes only octal
numbers in defining address and
decimal
other
expressions.
A
number (8 or 9) is illegal, causing
a question mark (?) to be printed
following the line in error.
1

1-5

(a)

simply

the

Type 1

INTRODUCTION
Table 1-2 (Cont.)
Forms of Address Expressions

1.3.2

Form of
Expression

Format of
Expression

Resulting Address
Expression (a)

Type 3

C or
C,k or
n,C or
C,C

Whenever C is typed as an element
of an ODT command, ODT replaces
this character with the contents
of the constant register
(see $C,
Table 3-1)
and then evaluates the
expression as a Type 2 address
(n,k).
In other words, the value
in the constant register referenced
by the C command has the same role
as the n or k that it replaces
in
an
address
expression.
For
example, when C is used in place of
n,
the
value
in the constant
register
selects
a
relocation
register
for
use
in printing out
task addresses (see section 3.1).
In all cases where C is used in
place of n,. the value of C must be
within
the range 0 through 7.
Whenever C is used in the place of
k,
the
value
in the constant
register so referenced may be any
16-bit
expression
value.
The
commands used
in accessing
and
modifying
the
contents of the
constant register are described
in
detail
in section 3.4 and Table
3-1.

Examples of Address Expressions

In the examples below of the three
values are assumed:
n

addressing

= Relocation register 3,

forms,

the

following

containing the value 003400.

Constant register, containing the value 000003.

Form of
Expression

Address Expression (a)
Keyboard Input

ODT Octal
Interpretation

Type 1

000005

Type 1

-17

177761

Type 2

3,0

003400

Type 2

3,150

003550

Type 2

3,-1

003377

1-6

~~.

INTRODUCTION
Form of
Expression

Address Expression (a)
Keyboard Input

ODT Octal
Interpretation

Type 3

000003

Type 3

c
c,o

Type 3

C,10

003410

Type 3

3,C

003403

Type 3

c,c+c

003406

003400

NOTE
For simplicity, most address expression
examples in this manual are Type l;
all
three types,
however,
are
equally
acceptable to ODT.

1-7

CHAPTER 2
ODT CHARACTERS AND SYMBOLS

User commands to ODT are composed of the characters and symbols
described below in Table 2-1.
This table summarizes all the ODT
commands in their available forms of use.
For the purposes of this
chapter,
the reader should und~rstand the notation presented in Table
1-1 and the basic concepts in the following paragraphs.
An open location is one whose contents have been printed by ODT for
user examination.
The value so printed is stored
in a special
register called the quantity register
(see $Q, Table 3-1).
The
contents of an open location are available for change. A closed
location is one whose contents are not immediately available for
change.
Typing one of the commands listed below when it is preceded by an
address expression opens the addressed location and prints its
contents. The format of the printed output is a function of the
command so issued.
In other words, these are interpretive commands
which may be used to print the contents of a specified location in any
one or all of several formats (modes). When issued, these commands
leave the current location open for further operations.

I
\

(Word
(Byte
(Word
(Byte
(Word

mode octal)
mode octal)
mode ASCII)
mode ASCII)
mode Radix-50)

Typing one of the seven
commands
listed
below
closes
the
currently-open location;
all but the carriage-return (<CR>) character
cause another location to be opened. The location so opened depends
on which of the other six commands is typed (see Table 2-1).
<CR> (Carriage Return)
<LF> (Line Feed)
"
(or up-arrow)
(or back-arrow)
@

>
<
In Table 2-1 and throughout this manual, the symbols <CR> and <LF> are
used to represent the pressing of the carriage-return and line-feed
keys, respectively.
As evident in the tables in this chapter, numerous ODT commands can be
entered in any one of several forms..
This flexibility stems from the

2-1

ODT CHARACTERS AND SYMBOLS

fact that ODT takes certain operational parameters and values from
tables within itself in performing specified commands. These tabLes
are described throughout this manual, particularly in Chapter 3, as
"ODT internal registers" or "ODT internal locations." These terms in
all cases refer to a block of memory within ODT which is reserved as a
temporary storage area for the dynamic debugging variables essential
to all ODT operations. These locations, consisting essentially of 17
sets of modifiable registers, are described in detail in section 3.4.
If required parameters for a given operation have already been stored
in one or more of these internal locations as the result of a previous
operation, a shorter form of a given command may suffice for a current
operation, since ODT takes the current value of the relevant internal
location(s) in executing a specified command. In the longer command
forms, however, required values are an immediate part of the command.
The various command forms are summarized briefly in the tables
throughout Chapter 2. Chapter 3 treats the command forms in detail in
conjunction with the discussions of ODT command sequences
and
functions.
Table 2-1
ODT Characters/Symbols
Meaning

Format
+ or space

Arithmetic operator.
Sum
the
preceding
argument and the following argument to form
the current argument.
Arithmetic operator. Subtract the following
argument from the preceding argument to form
the current argument.
Relocation register
operator.
Use
the
preceding 1-digit octal value to reference
one of ODT's eight relocation registers: the
contents of this register and the value of
the argument following the comma form the
current argument.
Thus, in ODT keyboard
commands, a comma separates a relocation
register specifier from an absolute value,
the combination of which is normally used to
specify relocatable address values in ODT
command sequences.

Radix-50 operator.
forming
Radix-50
3.16.4).

This command is used in
arguments (see section

Current location
operator.
Causes
the
address
of
the
last
explicitly-opened
location to be used as the current address
for ODT operations.
This is the address
assumed by the left angle bracket (<) command
to return to the previous sequence of opened
locations (see section 3.2.9). This address
is also implied in the use of the slash (/),
backslash (\), single quote ('), double quote
("), percent sign (%), and line-feed (<LF>)
commands.

2-2

ODT CHARACTERS AND SYMBOLS

Table 2-1 (Cont.)
ODT Characters/Symbols
Format

Meaning
Argument identifier.
Separates
multiple
arguments, allowing an address expression or
ODT register value to be identified.

Represents any 6-digit octal value that is
used as an argument in an ODT command. The
symbol k also represents any expression which
reduces
to
a
6-digit
octal
value.
Expressions may include special arguments
(such as $n, $x, C, or period) alone or in
combination with the arithmetic operators (+,
-, comma, or *). Expression constructions
are terminated by typing a specific ODT
command character or a semicolon (;).

Represents an octal integer in the range from
0 through 7. Decimal values are illegal in
ODT and are ~lagged with a question mark (?)
immediately following the illegal value.

Represents
an
argument
whose
special
attribute is an address of a location. On
input, any address
value
specified
is
interpreted by ODT as a 6-digit octal value,
regardless of
its
length.
Any
value
exceeding this limit is truncated to the
low-order 16 bits.
On output, ODT always
prints an address value as six octal digits.

Close
the currently-open location and accept the next command.
If <CR> is preceded by
k, the value k replaces the contents of the
currently-open location before it is closed.

Close the currently-open location, open the
next sequential location and
print
its
contents.
If <LF> is preceded by k, the
value k replaces the
contents
of
the
currently-open location before it is closed.

"' or k"'

Close the currently-open location, open the
immediately-preceding location and print its
contents.
(The up-arrow appears on some
keyboards
and is used in place of the
circumflex.) If "' is preceded by k, the value
k replaces the contents of the currently-open
location before it is closed.

2-3

ODT CHARACTEkS AND SYMBOLS
Table 2-1 (Cont.)
ODT Characters/Symbols
Format

Meaning

or k

Interpret the contents of the currently-open
location
as
a
PC-relative
offset and
calculate the address of the next location to
be
opened;
close
the
currently-open
location, and open and print the contents of
the
new
location thus evaluated.
(The
back-arrow appears on some keyboards and
is
used
in place of the under! ine.) If_ is
preceded by k,
the value
k replaces the
contents
of
the currently-open location
before it is closed.

@ or k@

Interpret the contents of the currently-open
location as an absolute address, close the
currently-open location,. and open and print
the contents of the absolute location thus
evaluated.
If @ is preceded by k, the value
k replaces the contents of the currently-open
location before it is closed.

> or k>

Interpret
the
low-order
byte
of
the
currently-open location as a relative branch
offset and calculate the address of the next
location
to
be
opened;
close
the
currently-open location and open and print
the contents of the relative branch location
thus evaluated.
If > is preceded by k,
the
value
k
replaces
the contents of the
currently-open location before it is closed.
The computation of this address is performed
by taking the
low-order
byte
of
the
currently-open location as a signed value,
multiplying this value by 2,
increasing
the
result by 2,
and adding
this sum to the
address of the currently-open location.

< or k<

Close the currently-open location (opened by
a _,
@,
or
> command) and reopen the word
location most recently opened by a /,
<LF>,
or~.
If the currently-open location was not
opened by a_, @, or >, then < simply closes
and reopens
the current location.
If < is
preceded by k,
the value k
replaces the
contents
of
the currently-open location
before it is closed.

Represents the address of one of eight user
program general
registers,
where n
is an
octal digit identifying RO
through R7
(see
section 3.3).

2-4

ODT CHARACTERS AND SYMBOLS
Table 2-1 (Cont.)
ODT Characters/Symbols
Format
$x or $nx

Meaning
Represents the address of one of 17 special
ODT internal register sets (see section 3.4),
where x is one of the following alphabetic
characters,
and
n is an octal
integer
identifying a given
location
within
a
register set.
These addressable register
sets exist within ODT in the following order:

Processor Status register
(hardware
PS), which is saved by ODT when a
breakpoint or user
program
fault
occurs

Directive Status Word register for the
user's task

Search argument register

Search mask register

Low memory limit register

High memory limit register

Constant register

Quantity register

Format register

Reentry vector register

Breakpoint address registers.

Breakpoint proceed count registers.

Breakpoint instruction registers.

Relocation registers.

SST vector registers.

SST (synchronous system
contents registers.

Device control LUN
number) registers.

trap)

stack

(logical

unit

Constant register operator.
Represents the
contents of special register $C (constant
register) .

Quantity register operator..
Represents the
contents of special register $Q (quantity
register) •

2-5

ODT CHARACTERS AND SYMBOLS

Table 2-1 (Cont.)
ODT Characters/Symbols
Format

Meaning

or a"

word mode ASCII operator.
Interpret
print the contents of the currently-open
the last previously-opened) location as
ASCII characters, and store this word in
quantity register ($Q).
If 11 is preceded
a, the value a is taken as the address of
location to be interpreted and printed.

and
(or
two
the
by
the

' or a'

Byte mode ASCII operator.
Interpret
print the contents of the currently-open
the last previously-opened) location as
ASCII character, and store this byte in
quantity register ($Q).
If ' is preceded
a, the value a is taken as the address of
location to be interpreted and printed.

and
(or
one
the
by
the

% or a%

Word mode Radix-50 operator.
Interpret and
print the contents of the currently-open (or
the last previously-opened) location as three
Radix-SO characters, and store this word in
the quantity register ($Q).
If % is preceded
by a, the value a is taken as the address of
the location to be interpreted and printed.

I or a/

Word mode octal operator.
Reprint
the
contents of the last word location opened,
and store this octal word
in the quantity
register
($Q).
If / is preceded by a, the
value a is taken as the address of a word
location to be opened and printed.

or a\

Byte mode octal operator.
Reprint
the
contents of the last byte location opened,
and store this octal byte in the quantity
register
($Q).
I f \ is preceded by a, the
value a is taken as the address of a byte
location to be opened and printed.

Interpret and print expression value k as six
octal digits and store this word in the
quantity register ($Q).

8 or 9,
RUBOUT,
or CTRL/U

Cancel the current command and await a new
command. The decimal value 8 or 9 is not a
legal character and thus, when
entered,
causes ODT to ignore the current command.
The RUBOUT and CTRL/U functions are not
operational
in RSX-llM, unless the terminal
driver supports transparent read/write
(a
system generation option).

Remove all breakpoints from the user task.

Remove the nth breakpoint from the user task.

2-6

ODT CHARACTERS AND SYMBOLS

Table 2-1 (Cont.)
ODT Characters/Symbols
Format

Meaning

a;B

Set the next available sequential
in the user task at address a.

breakpoint

a;nB

Set breakpoint n in the user task at
a.

Using the relocation register whose contents
are equal to or closest to (but less than)
the address of the currently-open location,
compute the physical distance (in bytes)
between the address of the currently-open
location and the value contained in the
selected relocation register;
print this
offset and store the value in the quantity
register ($Q).

Compute the physical distance (in bytes)
between the address of the currently-open or
the last-opened location and
the
value
contained in relocation register n; print
this offset and store the value in the
quantity register ($Q).

a;nK

Compute the physical distance (in bytes)
between address a and the value contained in
relocation register n; print this offset and
store the value in the quantity register

address

( $Q) •

F or kF

Fill memory locations within the address
limits specified by the low memory limit
register
($L)
and the high memory limit
register ($H) with the contents of the search
argument register ($A). If F is preceded by
k, the value k replaces the current contents
of $A before initiating the fill operation.

G or aG

Set BPT instructions in or restore
BPT
instructions to all breakpoint locations in
the task image, restore the Processor Status
Word
and
user
program registers, then
commence execution at the address specified
by the user Program Counter ($7). If G is
preceded by a, the value a replaces the
current contents of $7 before proceeding as
described above.

ao or a;kO

Calculate and print the PC-relative offset
and the 8-bit branch displacement from the
currently-open location to address a;
or
calculate and print the PC-relative offset
and the 8-bit branch displacement from the
specified address a to the specified address
k.

2-7

ODT CHARACTERS AND SYMBOLS
Table 2-1 (Cont.)
ODT Characters/Symbols
Format

Meaning

P or kP

Proceed with user program execution from the
current breakpoint location and stop when the
next breakpoint location is encountered or
the end of the program is reached:
or
proceed with program execution from
the
current breakpoint location and stop at this
breakpoint only after encountering it the
number of times specified by integer k.

Set all relocation registers to -1,
highest address value, i.e., 177777(8).

Set relocation register n to -1, the
address value, i.e., 177777(8).

a:R

Set relocation register O to address value a.

a:nR

Set relocation register n to address value a.

S or nS

Execute one instruction and print the address
of the next instruction to be executed: or
execute n instructions and print the address
of the next instruction to be executed.

W or kW
or m:W
or m: kW

Search
memory between
the address limits
specified by the low memory limit register
($L) and the
high
memory limit register
($H)
for words with bit patterns which match
those of the search argument specified in the
search argument register ($A). Compare each
memory word and the search argument for
equality under the mask specified in the
search mask register
($M).
When a match
occurs, print the address of the matching
location and its contents. If W is preceded
by k, the value k replaces the current
contents of $A before initiating the search.
If W is preceded by m (identified by the
semicolon that follows it), the value m
replaces the current contents of $M before
initiatinq the search.

the

highest

If W is preceded by both k and m, the current
contents of $A and $M are replaced with the
respective
values
so
specified
before
initiating the search.
NOTE
Testing under a search mask ($M)
results in a comparison of the
memory word and the search argument
only in those bit positions which
correspond to the bits set to one
(1)
in the mask:
all other bit
positions are ignored in the search
comparisons.
2-8

ODT CHARACTERS AND SYMBOLS
Table 2-1 (Cont.)
ODT Characters/Symbols

~··

Format

Meaning

N or kN
or m;N
or m;kN

Search
memory between the address limits
specified
by the low memory limit register
($L)
and the high memory limit register
($H) for words with bit patterns which do not
match those of the search argument specified
in the search argument register ($A). This
search is identical in form and function
to
the word
(W} search described above, except
that a test for inequality is performed.

E or kE
or m;E
or m;kE

Search
memory between
the address limits
specified by the low memory limit register
($L)
and the high memory limit register
($H).
Examine these locations for references
to the effective address specified
in the
search argument register ($A}, as masked by
the value specified
in the search
mask
register
($M).
(The mask should normally be
set to 177777 for
the E command.}
Such
references may be equal to, PC-relative to,
or a branch displacement to the location
specified
in $A.
If E is preceded by k, the
value k replaces the current contents of $A
before
initiating the search.
If E is
preceded by m, the current contents of $M are
replaced with the value m before initiating
the search.
If E is preceded by both k and
m,
the current contents of $A and $M are
replaced with the respective
values
so
specified before initiating the search.

L or kL
or a;L
or a;kL
or n;a;kL

List all word or byte locations in the task
between the address limits specified by the
low memory limit register ($L) and the high
memory limit register,
using
the listing
device specified
in the device control LUN
register ($1D).
If L is preceded by k,
the
value k replaces the current contents of $H
before initiating the list operation.
If L
is preceded by a, the value a replaces the
current contents of $L before initiating the
list operation.
If L is preceded by both a
and k, the values a and k replace the current
contents of $L and $H, respectively, before
initiating the list operation.
If L is also
preceded by the value n, this value selects
one of the device control LUN registers ($nD)
containing the logical unit number of the
device to be used in the list operation.

2-9

ODT CHARACTERS AND SYMBOLS

Table 2-1 (Cont.)
ODT Characters/Symbols
Format

Meaning

F or kF

Fill memory locations within the address
limits specified by the low memory limit
register
($L) and the high memory limit
register ($H) with the contents of the search
argument register ($A). If F is preceded by
k, the value k replaces the current contents
of the $A register before initiating the fill
operation.

Enable ODT's handling of all SST vectors, and
write the addresses of ODT's trap entry
points into the table used by the SVOB$
Executive directive.
(See Table 3-1 for a
discussion of the SST vector registers and
the $nV/ command.)

Exit from ODT and return control to
Executive of the host operating system.

2-10

the

CHAPTER 3

ODT COMMAND SEQUENCES AND FUNCTIONS

When ODT is initiated, its readiness to accept commands is indicated
through the underline
(_)
prompting character (back-arrow on some
terminals) at the left margin of the terminal. Most ODT commands can
then be issued in response to this character. This chapter describes
all the ODT command sequences and specific functions available to the
user.
Such keyboard interaction takes place using the characters and
symbols described in the preceding chapter.

3.1

PRINTING TASK ADDRESSES

Normally, when OD~~ prints user program addresses (as with the commands
<LF>, A, _, @, <, and >), it attempts to print them in relative form
(Type 2, see n;k, Table 1.2). If there is no relocation register
containing a value equal to the user task address to be printed, ODT
looks for the relocation register whose contents are closest to,
but
less than,
the address.
It then represents that address relative to
the bias value contained in the register. However, if no relocation
register fits this requirement, the user task address is printed in
absolute form.
Since the relocation registers are initialized to -1
(the highest address value),
the user task addresses are initially
printed in absolute form.
If the contents of any relocation register
are subsequently changed, it may then qualify for use in determining
task addresses in relative form, depending on the ODT command issued.
For example, assume that relocation registers 1 and 2 contain the bias
values 1000 and 1004,
respectively, and that all other relocation
registers contain much higher values. The following sequence might
then occur:
_774/012345 <LF>
000776 /024145 <LF>
1,000000 /106421 <LF>
1,000002 /143164 <LF>
2,000000 /112713 <CR>

;OPENS ABSOLUTE
;OPENS ABSOLUTE
;OPENS ABSOLUTE
;OPENS ABSOLUTE
;OPENS ABSOLUTE

LOCATION
LOCATION
LOCATION
LOCATION
LOCATION

774.
776.
1000.
1002.
1004.

The printout format is controlled by the format register
($F).
Normally, this register contains a default value of 0 (see $F, Table
3-1),
in which case, ODT prints addresses relatively
whenever
possible, as noted above.
The format register may be opened and
changed to a positive, nonzero value, however;
in this case, all user
task addresses are printed in absolute form.

3-1

ODT COMMAND SEQUENCES AND FUNCTIONS
3.2

COMMANDS FOR OPENING, CHANGING, AND CLOSING LOCATIONS

An open location is one whose contents have been printed by ODT for
examination and are thus available for change. A closed location is
one whose contents are not immediately available for change.
The contents of an open location may be changed by typing the new
value, followed by any ODT command which requires no argument (i.e.,
<CR>, <LF>, "', _, @, >, or <) • Note that leading zeros can be omitted
by the user.
Any command typed to open a location when another
location is already open, closes the currently-open location before
opening the new location.

3.2.1

Close Current Location:

When the <CR> key is typed while a location is open, that location is
simply closed and no new location is opened. When <CR> is preceded by
an argument k, that value replaces the current contents of the
location before that location is closed. Typing the <CR> key has no
effect on ODT when no location is open.

3.2.2

Open Next Sequential Location:

If the <LF> key is typed while a word location is open, i.e., if word
mode is in effect, ODT closes that location and opens the next
sequential word location, as shown below:
_1000/002340 <LF>
001002 /012740

;THE <LF> KEY IS TYPED AFTER THE
;PRINTOUT OF 002340, OPENING THE NEXT
;LOCATION

In the example above, typing the <LF> key causes ODT to print the
address and the contents of the next location automatically. The
value 012740 is thus made available for examination and may be
modified by typing a new value before issuing any command which closes
the location.
If a byte location is currently open, i.e., if byte mode is in effect,
typing the <LF> key opens the next sequential byte location.
Repetitive execution of the <LF> command causes ODT to open successive
words or bytes, depending on the mode of the currently-open location.

3.2.3

Open Word Location:

/ or a/

A word location may be opened using the command form a/,
the address of the location to opened, as shown below:
_1000/012746

where

;OPENS ABSOLUTE LOCATION 1000.

After the user types the slash
(/) , ODT automatically opens the
addressed location and prints its 6-digit octal contents, making this
value available for examination or change.

3-2

ODT COMMAND SEQUENCES AND FUNCTIONS
If the contents of an open location are not to be changed, the user
may issue a <CR> command or any other command which closes an open
location, without first typing an argument k. In the case of the <CR>
command, ODT thE~n closes the currently-open location, performs a
carriage-return and line-feed action, and prints the
prompting
character (_) to indicate its readiness to accept another command, as
shown below:
_1000/012746 <CR>

;CLOSES LOCATION 1000 AND AWAITS
;NEXT COMMAND.

If the user desires to change the contents of an open location, he may
do so by enterin9 the new value before issuing a command which closes
the location, as shown below:
_1000/012746 12345 <CR>

;MODIFIES LOCATION 1000 AND
;AWAITS NEXT COMMAND.

The slash command can also be used without an address argument to
reopen and reprint the contents of the word at the even-numbered
location last opened, as indicated in the following example:
_1000/012746 12345 <CR>
_/012345

;OPENS AND DISPLAYS CONTENTS OF
;PRECEDING WORD LOCATION.

This form of the slash command permits verification that a
was entered correctly in a preceding location.

new

value

The slash command may also be used in conjunction with the <LF>
command to open and print the contents of successive word locations.
After opening a location in word mode, repetitive execution of the
<LF> command displays consecutive task locations, as shown below:
_1002/000123 <LF>
001004 /123456 <LF>
001006 /154321 <LF>
001010 /0:24351

;REPETITIVE <LF> COMMAND DISPLAYS
;CONSECUTIVE WORD LOCATIONS.

In the sequence above, the <LF> command closes the currently-open
location before opening the next location. The last <LF> command in a
series of such commands leaves the current location open for any
desired operation, as reflected above.
If an odd-numbered address is specified in opening a location, the
slash command causes the location to be opened in byte mode. In this
case, ODT commands then issued operate on byte locations and values,
as indicated in the following sequence:
_1001/123 321 <CR>
_/321 <LF>
_001002 /021 <LF>
_001003 /010 <LF>
_001004 /.201

;LOCATION 1001 OPENED IN BYTE
;MODE. SUBSEQUENT COMMANDS OPERATE
;ON BYTE LOCATIONS.

Word mode can then be restored, if desired, by
closing
the
currently-open byte location and opening another location on an even
address boundary, as shown below in the continuation of the preceding
sequence:
_001004 /201 <CR>
_1006/102054

;<CR> CLOSES CURRENT LOCATION.
;NEXT LOCATION OPENED ON WORD
;BOUNDARY, RESTORING WORD MODE.

3-3

ODT COMMAND SEQUENCES AND FUNCTIONS
3.2.4

Open Byte Location:

\ or a\

As noted in the preceding section, ODT also operates on byte locations
and values.
The command form a\ is provided in ODT for simplifying
the examination and modification of octally represented byte values,
including those that fall on odd address boundaries.
(On Teletypes,
the backslash is typed by holding down the SHIFT key and typing L.)
When this command form is used, the address value a, specified prior
to the command, may be either odd or even. A byte location may be
opened, as shown below:
_1001\002

;LOCATION 1001 OPENED IN BYTE MODE.

After the user types the address of the byte location to be opened,
followed by the backslash
(\) , ODT causes the contents of the
addressed location to be printed as a 3-digit octal value.
If the contents of the byte location are not to be changed,
the <CR>
command, or any other command which closes an open location, may be
issued without first typing an argument k.
In the case of the <CR>
command, ODT then closes the currently-open byte location, performs a
carriage-return and line-feed, prints the prompting character (_), and
awaits another command, as shown below:
_1001\002 <CR>

;CLOSES LOCATION 1001 AND AWAITS
;NEXT COMMAND.

Should the user desire to change the contents of an open byte
location, he may do so by entering the new value before issuing a
command which closes the location, as reflected below:
_1001\002 10 <CR>

;MODIFIES LOCATION 1001 AND AWAITS
;NEXT COMMAND.

Similar to the slash (/) command, the backslash character may be used
without an address argument to reopen and reprint the contents of the
byte at the location last opened. This use of the byte command is
illustrated in the following sequence:
_1001\002 10 <CR>
_\010
Thus, the alteration of
verified.

;OPENS AND DISPLAYS CONTENTS OF THE
;LAST OPENED BYTE LOCATION.
a

previously-opened

byte

location

can

The <LF> command is also useful in conjunction with the backslash
command, permitting successive byte locations in the task to be
examined. After opening a location in byte mode, repetitive typing of
the <LF> command displays consecutive byte values, as shown below:
_1003\004 <LF>
001004 \120 <LF>
001005 \203 <LF>
001006 \310

;REPETITIVE <LF> COMMAND DISPLAYS
;CONSECUTIVE BYTE LOCATIONS.

The <LF> command closes the currently-open location before opening the
next location;
the last such command issued, however, leaves the
current location open for any desired operation, as shown above.

3-4

ODT COMMAND SEQUENCES AND FUNCTIONS

If a word location is currently open, typing the backslash command
causes the word's low-order byte to be displayed without ODT leaving
word mode:

3.2.5

_1010/000005 \005

;DISPLAYS LOW-ORDER BYTE.

Open Preceding Location:

A or kA

If the circumflex (or up-arrow) key is typed when a location is open,
ODT closes the currently-open location and opens and prints the
contents of the immediately preceding location.
(On Teletypes, the
circumflex is typed by holding down the SHIFT key, and typing N. The
use of the circumflex is reflected in the following sequences:
_1000/002340 <CR>
_1002/012740 . .
001000 /002340
_0,232/005046 <LF>
0,000234 /012746 . .
0,000232 /005046

;LOCATION 1000 IS OPENED AND
;EXAMINED.
;LOCATION 1002 IS OPENED AND
;EXAMINED, FOLLOWED BY CIRCUMFLEX
;COMMAND.
;PRECEDING LOCATION IS OPENED AND
;PRINTED.
;LOCATION 232, RELATIVE TO RELOCATION
;REGISTER 0, IS OPENED AND EXAMINED.
;NEXT LOCATION IS OPENED AND PRINTED,
;FOLLOWED BY CIRCUMFLEX COMMAND.
;PRECEDING LOCATION IS OPENED AND
;PRINTED.

If a byte location is currently open, issuing the circumflex command
opens the preceding byte location and makes its contents available for
examination or change, as shown below:
_1003\046 <LF>
001004 \003 . .
001003 \046

;LOCATION 1003 IS OPENED IN BYTE
;MODE.
;NEXT BYTE LOCATION IS OPENED,
;FOLLOWED BY CIRCUMFLEX COMMAND.
;PRECEDING BYTE LOCATION IS OPENED
;AND PRINTED.

If the command form k"' is used, the expression value k modifies the
contents of the currently-open location before that location is
closed, as shown in the following sequences:
_0,230/005406 <LF>

;LOCATION 230, RELATIVE TO RELOCATION
;REGISTER O, IS OPENED.
0,000232 /000626 12345 "' ;NEXT LOCATION IS OPENED AND
;MODIFIED TO CONTAIN 012345. FOLLOWED
;BY CIRCUMFLEX COMMAND.
0,000230 /005406 <LF>
;PRECEDING LOCATION IS OPENED AND
;PRINTED.
0,000232 /012345
;CONTENTS OF MODIFIED LOCATION ARE
;VERIFIED.

If a location is not currently open,
typing the circumflex command
opens
and prints the contents of the last previously-opened word (or
byte) location, as shown in the following sequence:
_0,236/000100 <CR>
··~

0,000236 /000100

;RELOCATABLE ADDRESS 236 IS OPENED
;AND CLOSED.
;CIRCUMFLEX OPENS AND PRINTS LAST
;OPENED LOCATION.
3-5

ODT COMMAND SEQUENCES AND FUNCTIONS

3.2.6

Open PC-Relative Location:

or k

If the underline (or back-arrow) key is typed when a location is
currently open,
the contents of that location are added to its
address+2 (PC value), yielding the address of the location to be
opened.
(On Teletypes,
the underline is typed by holding down the
SHIFT key, and typing 0.) This computation is
effectively
a
PC-relative reference.
After this calculation, the current location
is closed, the new location is opened, and its contents are printed,
as shown in the following sequences:
1000/000040
001042 /052470

;UNDERLINE OPENS PC-RELATIVE
;LOCATION AND PRINTS ITS CONTENTS.

If the currently-open location contains an odd value when the
underline command is issued, the referenced location is not on a word
boundary, and so is opened as a byte, as shown in the following
sequences:
_0,232/012345
0,012601 /041

;PC-RELATIVE ADDRESS IS CALCULATED,
;CALCULATED ADDRESS IS THAT OF A
;BYTE.

0,422/000001
0,000425 /246

;SAME AS ABOVE.

~~.

When the command form k_ is used, the expression value k modifies the
contents of the currently-open location, and this new value is then
used in the calculation of the PC-relative address of the location to
be opened and printed, as shown in the following sequences:
0,232/012345 123456

0,123712 /020301

3.2.7

Open Absolute Location:

;LOCATION 232, RELATIVE TO
;RELOCATION REGISTER 0, IS
;OPENED AND MODIFIED TO
;CONTAIN 123456, FOLLOWED BY
;UNDERLINE COMMAND.
;PC-RELATIVE LOCATION IS
;OPENED AND PRINTED.

@ or k@

The @ sign typed when there is a currently-open location takes the
contents of that location as the address of the next location to be
opened.
(On Teletypes, the @ sign is typed by holding down the SHIFT
key, and typing P.) The currently-open location is then closed, and
the new location is opened. The following sequences reflect the use
of this command:
_1006/001024 @
001024 /000500

;USES CONTENTS OF CURRENT
;LOCATION AS ADDRESS OF NEXT LOCATION
;TO OPEN.
;LOCATION 1024 IS OPENED AND LTS
;CONTENTS PRINTED.

_lOO;R

;SETS RELOCATION REGISTER 0 TO 100(8)

_0,232/000456 @

;SAME ACTION AS ABOVE, IN
;RELOCATABLE FORMAT.
;LOCATION 456 OPENED AND
;CONTENTS PRINTED.

0,000356 /005046

3-6

ODT COMMAND SEOUENCE:S AND FUNCTIONS
If the command form k@ is employed, the expression value k modifies
the contents of the currently-open location, and this new value is
then taken as the address of the next location to be opened, as shown
in the following sequences:
_1006/001024 2100@
002100 /177774

;LOCATION 1006 IS MODIFIED TO
;CONTAIN 002100. THIS VALUE IS
;THEN USED TO OPEN NEXT LOCATION.

_370;R

;SET RELOCATION REGISTER 0 TO
;BIAS VALUE OF 370(8) FOR MODULE.
;CONTENTS OF RELOCATABLE ADDRESS 600
;ARE MODIFIED TO CONTAIN 012746. THIS
;VALUE IS THEN USED TO CALCULATE
;ADDRESS OF NEXT LOCATION TO BE
;OPENED.
;EVALUATED ADDRESS IS OPENED AND ITS
;CONTENTS PRINTED.

_0,600/012345 12746 @

0,012356 /027117

In the example above, note that the relocatable address of the next
location opened
(0,012356) is represented relative to the bias value
370(8) contained in relocation register
0.
The accuracy of this
calculation is verified by adding the value 370(8) to the value
012356(8), yielding the sum 012746(8).
3.2.8

Open Relative Branch Offset Location:

> or k>

When the right-angle bracket
(>)
command is issued for an open
location, ODT takes the low-order byte of this location to calculate a
relative branch offset in determining the address of the next location
to be opened.
The current location is closed when this command is
executed.
The relative branch offset, i.e., the address of the next location
be opened, is calculated as follows:
1.

Take the low-order byte of the currently-open
signed value.

Multiply this value by 2.

Add the result of Step 2 to the address of the
location+2 (PC value).

location

to
a

currently-open

The examples below show the use of the relative branch offset command:
_1032/000407 >
001052 /001456

;TAKES THE LOW-ORDER BYTE OF THE
;CURRENT LOCATION AS RELATIVE
;BRANCH OFFSET TO OPEN NEXT
;LOCATION.

0,66/005046 >
0,000204 /000601

;SAME OPERATION AS ABOVE, EXCEPT
;RELOCATABLE ADDRESS VALUES ARE
;USED.

3-7

ODT COMMAND SEQUENCES AND FUNCTIONS
If the command form k> is used, the expression value k modifies the
contents of the currently-open location, and the low-order byte of
this new value is then used in the calculation of the relative branch
offset location, as shown in the following sequences:
_1032/000407 301>
000636 /000010

;LOCATION 1032 IS MODIFIED TO
;CONTAIN 000301. LOW-ORDER
;BYTE OF THIS NEW VALUE IS
;THEN USED IN DETERMINING RELATIVE
;BRANCH LOCATION.

_0,232/000456 134561 >
0,000576 /002340

;RELOCATABLE LOCATION 232 IS
;MODIFIED TO CONTAIN 134561. LOW;ORDER BYTE OF THIS NEW VALUE IS
;THEN USED IN CALCULATING RELATIVE
;BRANCH LOCATION.

Note in the first example above illustrating the k> command form, that
the byte value 301 is interpreted by ODT as a negative value (the
high-order bit in this byte is 1).
Therefore,
a negative branch
offset results, causing location 636 (a lower physical address) to be
opened and its contents printed.

3.2.9

Return to Interrupted Sequence:

< or k<

The left-angle bracket command (<) can be used immediately after
issuance of any of the following add~ess calculation commands:
1.

Open PC-relative location (_)

Open absolute location (@)

Open relative branch offset location (>)

the

(see section 3.2.6).

(see section 3.2.7).
(see section 3.2.8).

The user can issue any of these three commands in any order after
explicitly opening a word location with a / , <LF>, or A . The /, <LF>,
and A commands are explicit in that they open a specified location,
the word following a currently-open location, or tqe word preceding a
currently-open location, respectively. They do not depend on the
contents of the open location as the address calculation commands
mentioned above do.
The left angle bracket command
(<)
causes ODT to
close
the
currently-open location,
and reopen the word location most recently
opened by a / , <LF>, or
If the currently-open location was not
opened by a
, @, or > command, then < merely closes and reopens the
current location itself.
A.

The effect of the < command is reflected in the following sequences:
_10000 ;R
_0,1030/000174 <LF>
0,001032 /000200 @

000200 /007020 @
007020 /000000 <
0,001032 /000200

;SETS RELOCATION REGISTER 0 TO 10000
;OPENS RELOCATABLE 1030; <LF> OPENS
;NEXT WORD
;@ OPENS LOCATION 200 IN ABSOLUTE
;FORMAT BECAUSE NO RELOCATION
;REGISTER'S CONTENTS ARE LESS THAN
;OR EQUAL TO 200
;@ OPENS 7020 IN ABSOLUTE FORMAT (NO
;RELOC. REG. CONTENTS < OR = TO 7020)
;< REOPENS RELOCATABLE 1032

3-8

ODT COMMA.ND SEQUENCES AND FUNCTIONS
_1036/021346 ,..
1034 /101036 102074 /000000 @
000000 /000000 >
000002 /000102 <
001034 /101036

;OPENS 1036; "' OPENS PRECEDING WORD
;OPENS PC RELATIVE LOCATION.
;OPENS ABSOLUTE LOCATION.
;OPENS RELATIVE BRANCH OFFSET
;LOCATION.
;RETURNS TO LAST EXPLICITLY-OPENED
;LOCATION.
;OPENS AND PRINTS CONTENTS OF
;LOCATION 1034.

The contents of any location opened by one of the three address
calculation commands may be altered,
if desired, before issuing a
command which closes that location. This option is illustrated in the
following sequences:
_1064/000276 @
000276 /000340 336_
000636 /000000 302>
000444 /026474 474@
000474 /015325 <
001064 /000276

3.3

ACCESSING USER PROGRAM GENERAL REGISTERS:

ODT has a set of fixed locations which are used to store the current
values of the user program's general registers when a breakpoint
occurs. Thus, the~ current state of the user program is preserved so
that task execution can be resumed normally when control is returned
to the user through the execution of the G (Go)
or P (Proceed)
commands
(see section 3.6). These registers, numbered 0 through 7,
can be examined with a command of thE~ following form:
_$n/
where n represents an octal integer representing the desired register.
When the slash is typed, the contents of the specified register are
automatically printed by ODT, making this value available
for
examination or change. The user can change the contents of a general
register by issuing a command of the form $n/a <CR>, where n
represents the octal register specifier, and a represents the new
value to be entered.
The following examples show how the user
program's general registers are opened and modified:
_$0/000033 <CR>
_$4/000474 464 <CR>

;REGISTER 0 IS EXAMINED AND CLOSED.
;REGISTER 4 IS OPENED, MODIFIED TO
;CONTAIN 000464, AND CLOSED.

Any register modification just completed, as shown in the $4 line
above,
can be verified by typing a slash in response to ODT's
prompting character. Thus, the continuation sequence is:
_/000464

;PRINTS THE CONTENTS OF THE
;PREVIOUSLY-OPEN LOCATION.

Note that the <LF>, "', _, or @command may be used in connection
a user program general register when that register is open.

3-9

with

ODT COMMAND SEQUENCES AND FUNCTIONS
3.4

ACCESSING SPECIAL ODT INTERNAL REGISTERS:

$x or $nx

ODT contains a number of fixed locations which are used as registers
for temporary storage of values essential to debugging operations. In
addition, these registers provide a mechanism through which the
current state of the user program is preserved when a breakpoint
occurs, saving and restoring such values as the Processor Status Word
and the user program stack pointer during debugging operations. These
internal registers, which are accessible to the user in the same
manner as any location within the task image, are described in detail
in Table 3-1.
The command form $x/ is used to access an ODT internal register, where
x represents the alphabetic register identifier. The processor status
register, for example, can be accessed with the following command:
_$S/000011

;THE COMMAND $S/ OPENS THE STATUS
;REGISTER AND PRINTS ITS CONTENTS.

In response to the $S/ command, ODT prints the 16-bit Processor Status
Word in 6-digit octal format.
If desired, any new value can be
entered into the register, followed by a command which closes the
register.
The command form $nx/ is used to access an internal register set
consisting of several separate locations, where x represents the
alphabetic register identifier (as above), and n represents an octal
integer referencing a particular location within the register set.
Relocation register 7, for example, can be accessed with the following
command:
_$7R/000040

;THE COMMAND $7R/ OPENS RELOCATION
;REGISTER 7 AND PRINTS ITS CONTENTS.

The contents of this register may also be modified, if desired, by
entering the new value and issuing a command which closes the
location.
All the ODT internal registers described in Table 3-1 can be
and modified in similar fashion.

accessed

Note in Table 3-1, that the value a, k, or n may appear in connection
with the generic command forms used to open the ODT internal registers
(e.g., $C/a, $F/n, $A/k, etc.). These symbols represent new values
that may be entered into the register if the current value displayed
upon opening the register is not desired. Also, these symbols may be
used in connection with other ODT commands (described in Table 3-1 and
elsewhere throughout this manual) which automatically enter parameters
into specific internal registers without overtly opening the locations
to which these parameters apply.
The symbols a, k, and n are
described in the context of the operation being performed and, in all
cases, represent the specific parameters or arguments defined by the
user to serve current debugging purposes.

"'I
3-10

"----------------------------------------------

ODT COMMAND SEQUENCES AND FUNCTIONS

Table 3-1
Internal Register Access/Modification Commands
Command

Function

Processor status register.
Contains the Processor
Status Word after the execution of the last user
program instruction prior to the occurrence of the
breakpoint.
Although this register is accessible to
the user through the $8/ command,
it is set by the
Executive of the host operating system and normally
should not be changed by the user.
This register
provides the mechanism through which the Processor
Status Word may be examined during a debugging session.
For a detailed description of the Processor Status
word, refer to Appendix A.

Directive Status Word register. Contains the Directive
Status Word
(DSW)
of the user's task.
This word
contains information on either the success, or specific
cause of rejection of the most recently executed
directive. The DSW is saved across breakpoints, and is
available for examination and modification through the
$W/ command.
(This status word is discussed more fully
in the Executive Reference Manual of the host system.)

Constant register. Set by the user to any 16-bit value
representing an address (a) or an expression value (k)
through the $C/a <CR> or the $C/k <CR> commands,
respectively.
Both command forms ara identical in
function and are shown to represent the possible uses
of the values so entered.
For example, any value
entered in the constant register may be used by typing
C as an argument in an ODT command. The possible uses
of this value are illustrated as a Type 3 address in
Table 1-2.
The constant register
is described in
further detail in section 3.16.2.

Format register. Set by the user to an octal value (n)
through the $F/n <CR> command. When set to zero (the
default value), all user task addresses are printed by
ODT in relative form when appropriate (as described in
section 3.1). All other values of n cause user task
addresses to be printed in absolute form.

Search mask register. Set by the user to a word or
byte search mask value through the $M/m <CR> command.
A mask value may also be set in those commands which
initiate search operations (see sections 3.8.1 through
3.8.3). This register is initialized by ODT to minus
one
(-1), 177777(8). Thus, unless otherwise modified,
all bit positions in the search argument (see $A below)
and the memory word/byte will be compared in a search
operation.

3-11

ODT COMMAND SEQUENCES AND FUNCTIONS

Table 3-1 (Cont.)
Internal Register Access/Modification Commands
Command

Function

Search argument register. Set by the user to a word or
byte search argument (k) through the $A/k <CR> or the
$A\k <CR> commands, respectively.
A search argument
may also be set in those commands which initiate search
operations (see sections 3.8.l through 3.8.3).

Low memory limit register.
Set by the user to an
address value
(a)
through the $L/a <CR> command,
establishing the lower memory limit for all ODT search,
list,
and
fill
operations which reference this
register. This register is initialized by ODT to zero
(0). Either absolute or relocatable address values may
be entered into this register.

High memory limit register. Set by the user to an
address value
(a)
through the $H/a <CR> command,
establishing the upper memory limit for all ODT search,
list,
and
fill
operations which reference this
register. This register is also initialized by ODT to
zero
(0). As with the $L register, either absolute or
relocatable address values may also be entered into
this register.

Quantity register.
Set automatically by ODT to the
last value printed on the console. This register is
described in further detail in section 3.16.3.

Reentry vector register.
This register is normally set
to one
(1)
by the user through the $X/n <CR> command
when an initial debugging pass has been completed, thus
allowing the user program to be executed directly
without again reentering ODT.
If set to one
(1),
the
task then starts at its normal entry-point address or
at the address specified by the user
in general
register
7
(see section 3.3),
rather than at ODT's
starting address.
The use of this
register
is
described in further detail in section 3.17.

$nR

Relocation register n.
One of eight
(n)
register
locations which may be set by the user to a value (a)
through the a;nR command or the $nR/a <CR> command.
A
value set in a specified register location represents
the relocation bias of a given relocatable object
module of interest during the debugging session. Once
set, the contents of a given location enable ODT to
print user task addresses relative to a base address.
Both positive and negative offsets
(biases)
can be
calculated by ODT using these register locations (see
section 3.11). Also, when the user opens a given
location in a relocatable module,
the value in the
associated relocation register enables ODT to calculate
the relocated address of the user task location (see
section 3.12). Thus, relocatable code in the assembly
listing can easily be associated with the addresses of
relocated code during the debugging session.
This
register
is initialized by ODT to minus one (-1},
177777(8).
3-12

·------------------------------------------

OD'l~

COMMAND SEQUENCES AND FUNCTIONS

Table 3-1 (Cont.)
Internal Register Access/Modification Commands
Command

Function

$nB

Breakpoint· address register n.
One of eight
(n)
locations which may be set by the user to an address
value~ (a) through the a;B or a;nB commands (see section
3.5)
or the $nB/a <CR> command. These user-specified
addresses identify breakpoint addresses in the user
task
whose contents are to be swapped with BPT
instructions in an associated breakpoint instruction
register (see $nI below). This swapping process occurs
upon execution of the G command when the debugging
session is initiated or upon execution of the P command
when task execution is resumed from a breakpoint
location
(see section 3.6).
The breakpoint address
registers are described in further detail
in section
3.5.

$nD

Device control LUN register n.
One of three
(n)
locations which may be set by the user to a value (k)
through the $nD/k <CR> command, where the values
defined for n and k have the following significance:
Value! n

Value k

()

- User terminal device logical unit number
(see Note below) . The value of k in this
location ($OD) is normally 000007(8).

- Console listing device logical unit number
(see Note below). The value of k in this
location ($1D) is normally 000010(8).

- QIO event flag number The value of k in
this location
($2D) is normally a default
value of 000034(8).
NOTE

The user terminal device LUN
(TI:)
and the
console list device LUN (CL:) are assigned by
the Task
Builder,
which
examines
the
UNITS= Keyword option (having a default value
of 6).
The LUN n+l is assigned to the user
terminal device, and the LUN n+2 is assigned
to the console list device, where n is the
default value 6 or the value used as the
argument to the UNITS= Keyword option. Thus,
$OD normally contains 000007(8),
and $1D
normally contains 000010(8).
$nI

Breakpoint instruction register n.
One of eight
(n)
locations which may be set by ODT to contain BPT
instructions.
These BPT instructions are swapped. with
user program instructions at the breakpoint locations

3-13

ODT COMMAND SEQUENCES AND FUNCTIONS
Table 3-1 (Cont.)
Internal Register Access/Modification Commands
Command
$nI
(Cont.)

Function

defined through the breakpoint address register
(see
$nB above).
This swapping
process
occurs
upon
execution of the G command when the debugging session
is initiated or upon execution of the G or P command
when task execution is resumed from a breakpoint
location
(see section
3.6).
This
register
is
initialized by ODT to BPT instructions, i.e., op code
000003 ( 8) •

$nG

$nV

Breakpoint proceed count register n.
One of eight
(n)
locations which may be set by the user to a proceed
count value (k) through the kP command or
the $nG/k
<CR> command.
The proceed count value set in each of
these locations is associated with a given breakpoint
address,
as defined by the user
in the breakpoint
address register (see $nB above).
It is sometimes
useful,
for
example,
to set a breakpoint in a loop.
After the breakpoint occurs, the user may type the kP
command
(see section 3.6)
to resume execution.
The
program then executes through the loop k number of
times before again recognizing the breakpoint.
Each
time the breakpoint location is encountered,
the
proceed count value in the associated register location
is decremented.
When the count reaches zero
(0),
the
breakpoint is again recognized, suspending user task
execution and transferring control to ODT for
any
desired
debugging
operations.
This register
is
initialized by ODT to one (1).
SST vector register n.
One of eight (n) locations that
contain entry-point addresses of ODT routines for
handling synchronous system traps.
These traps occur
during user program execution as a result of certain
hardware-detected errors and programming conditions.
The value n refers to a given SST vector address
location, as listed below.
Each of these locations
contains a pointer to an ODT error-handling routine
which evaluates the SST error condition and prints out
an appropriate console error message (see section 5.2).
If a user program and ODT both have SST vectors enabled
for
a condition that then occurs, ODT receives the
trap.
As released,
ODT has seven vectors enabled.
Only vector number
6 (TRAP instruction executed) is
disabled.
OD~'s handling of vector 6 can be enabled by
the user through the V command.
The V command enables
ODT's handling of all SST vectors,
and writes the
addresses of ODT's trap entry points into the table
used by the SVDB$ Executive directive
(see
the
Executive Reference Manual of the host system).

$nV

Value n
0

SST Vector Register
- Odd address reference in word
instruction.
(Also,
on some PDP-11 processors
(e.g.,
PDP-11/45),
the execution of an
illegal
instruction
is trapped here rather
than
through SST vector 4.)
3-14

~--,

"""·

ODT COMMAND SEQUENCES AND FUNCTIONS
Table 3-1 (Cont.)
Internal Register Access/Modification Commands
Command
$nV
(Cont.)

!<'unction
Value n

SST Vector Register

- Memory protect violation

- T-bit trap or BPT instruction executed.

3
4

- !OT instruction executed.
- Reserved or illegal instruction executed.
- Non-IAS/RSX-11 EMT instruction executed.
- TRAP instruction executed.
- PDP-11/40 floating point exception error.

5
6
7

(segment fault).

These vector
locations are accessible to the user
through
the
$nV/ command in a manner similar to any
other ODT internal register, where the value n selects
one of the eight locations listed above.
Normally,
these ODT locations are not manipulated by the user.
However,
the user has the option of handling some or
all of the SST traps (except the BPT instruction)
that
may occur during program execution.
In this case, the
user may set the corresponding SST vector
location
in
ODT to
zero
(0), thereby causing the user program to
trap to an SST processing routine within itself,
i.e.,
the trap will
reference the user SST vector address
directly without invoking ODT control.
Such an option
obviously
assumes that the user program contains
appropriate routines for handling SST error conditions.
$nE

3.5

SST stack contents register n.
One of
three
(n)
locations
(where n is equal to 0, 1, or 2) into which
the top three items on the user program stack are
placed when a synchronous system trap occurs (see $nV
above).
These stack
items have different values,
depending on the type of
trap taken.
(Consult the
Executive Reference Manual of the host operating system
for
a discussion of synchronous system traps.) These
locations, containing user task information of interest
following an SST interrupt, can be examined through the
$nE/ command, where n selects one of the three register
locations, as noted above.

TASK BREAKPOINT COMMANDS:

a;B, a;nB, B, or nB

Breakpoints must be set in the first word of an instruction.
When set
through one of the commands described below, ODT places the address of
each breakpoint location in an associated breakpoint address
register
(see $nB, Table 3-1).
When a G or P command is issued to initiate or resume task execution
(see section 3.6),
ODT swaps the user instructions in the specified
breakpoint locations with BPT instructions
in
the
breakpoint
instruction registers
(see $nI, Table 3-1).
Later, as a breakpoint
location is encountered during task execution, the BPT instruction in
that location causes control to be transferred to ODT at the address
contained in SST vector register 2 (see $nV, Table 3-1).

3-15

ODT COMMAND SEQUENCES AND FUNCTIONS
The BPT instruction,
in connection with
the
PDP-11
hardware
facilities,
thus serves as a
simple and efficient mechanism for
calling a
debugging aid.
As the final
consequence
of
this
software-generated trap, ODT suspends task execution and restores the
original user instruction to the breakpoint location.
Since ODT
retains control,
the user can then perform any desired debugging
operations from the current breakpoint location.
It is important to note that the original user instruction
is always
restored to the current breakpoint location when the breakpoint trap
occurs, ensuring that all user
task
instructions will be executed
during the course of a debugging session if the program is allowed to
proceed to completion.
It should also be noted that debugging overlaid tasks presents special
considerations
in
setting
and maintaining breakpoints.
Since
breakpoints established for the current segment do not remain valid
for
a
subsequent segment, all breakpoints should be removed from the
current segment before a
new segment
is loaded.
Otherwise,
task
instructions saved from breakpoint locations in the current segment
will later be swapped into a new segment,
thus
implanting
invalid
instructions
and
corrupting
the program.
It
is recommended,
therefore, that tasks be non-overlaid for debugging.
Up to eight breakpoints, numbered 0 through 7, can be set at any given
time.
The command which accomplishes this action takes the form:
a;B
where a represents the address of the breakpoint location.
Repetitive
execution of this command can be used to establish all eight (0
through 7) breakpoint locations,
since each of the addresses so
defined is entered sequentially into the breakpoint address registers
(see $nB, Table 3-1).
Specific breakpoints can be
command:

set

changed

through

the

following

a;nB
where a represents the address of the desired breakpoint location, and
n represents one of eight (0 through 7) such specific breakpoints.
The examples below illustrate how breakpoints are set and changed:

_B
__ 1020 ;B
_1030;B
__l 0 4 0; B
__ 10 32; lB

;CLEAR ALL BREAKPOINTS.
;SET BREAKPOINT 0.
;SET BREAKPOINT 1.
;SET BREAKPOINT 2.
;RESET BREAKPOINT 1.

The B command typed alone removes all breakpoints in the user task, as
shown in the initial command of the preceding sequence.
The command
form nB removes only the specified breakpoint, as shown in the last
command below, where n represents any one of the eight (0 through 7)
breakpoints currently in effect.
The following sequence shows how
breakpoints are set, changed, and removed:

3-16

ODT COMMAND SEQUENCES AND FUNCTIONS
_1020;08
_1030;1B
_1064;28
_1220;3B
_1324;4B
_1032;1B

;SET BREAKPOINT 0 AT LOCATION 1020.
;SET BREAKPOINT 1 AT LOCATION 1030.
;SET BREAKPOINT 2 AT LOCATION 1064.
;SET BREAKPOINT 3 AT LOCATION 1220.
;SET BREAKPOINT 4 AT LOCATION 1324.
;CHANGE BREAKPOINT 1 TO LOCATION
;1032.
;REMOVE BREAKPOINT 3.

- 3B

The command form $nB/ references the address of the nth breakpoint, as
stored in the nth breakpoint address register (see $nB, Table 3-1).
Assuming that the previous command sequence is still in effect,
the
user may reference breakpoint 0 through the following command.
_$08/001020

;OPENS BREAKPOINT REGISTER 0 SET IN
;PREVIOUS SEQUENCE.

The command $nB/ thus opens breakpoint address register n, causing its
contents to be printed. Continuing with the current command sequence,
the user may examine the contents of successive breakpoint address
registers by repetitively typing the <LF> key, as shown below:
_$0B/001020
$1B /001032
~28 /001064
$3B /000364

;OPENS BREAKPOINT 0.
;BREAKPOINT 1, OPENED BY LINE FEED.
;BREAKPOINT 2, OPENED BY LINE FEED.
;BREAKPOINT 3, OPENED BY LINE FEED.

All eight breakpoint address registers can be examined in this manner.

3.6

PROGRAM EXECUTION COMMANDS:

G or aG and P or kP

Two general command forms are available for
running the user task:
the G (Go) command and the P (Proceed) command. An alternate form of
each command is also available which takes an argument,
as described
in the following paragraphs. The G command exists primarily to begin
program execution at the user task's transfer address,
and the P
command is used to resume program execution at the next logical
instruction after a breakpoint has occurred.
When the G command is executed, the BPT instructions in the breakpoint
instruction registers
(see $nI, Table 3-1) are swapped with the user
instructions in the task image locations defined in the breakpoint
address registers (see ~nB, Table 3-1). Task execution then begins at
the program's entry-point address, i.e., the address contained in the
user task's program counter (PC).
If an address argument a is specified with the G command, the swapping
of BPT instructions and user task instructions at breakpoint locations
occurs as described above,
but program execution begins at the
specified task address.
For example, the command:
lOOOG

initiates execution at task location 1000.
Note that any address
argument used with the G command must specify an even address, i.e., a
word location boundary.
The program runs until a breakpoint is
encountered or until the end of the program is reached.
(A program
that is in an infinite loop must be aborted and then restarted.)

3-17

ODT COMMAND SEQUENCES AND FUNCTIONS
When a breakpoint is encountered,
the contents of the user task
general registers are stored in ODT locations $0 through $7 (see
section 3.3). In addition, task execution is suspended,
the user
program instructions are restored to all breakpoint locations, and ODT
prints a console message indicating the occurrence of a breakpoint.
This message takes the following form:
nB:a
where n represents the breakpoint number, and a represents the address
of the breakpoint location. The prompting character (_) then appears
on the following line to indicate ODT's readiness to accept any valid
command, as shown in the sequences below:
_1Ul0;3B

_lOOOG
3B:001010

;BREAKPOINT 3 IS SET AT LOCATION
;1010.
;EXECUTION IS STARTED AT LOCATION
;1000.
;EXECUTION STOPS AT BREAKPOINT 3, AND
;THE ADDRESS OF THE BREAKPOINT
;LOCATION IS PRINTED.

To continue program execution from a breakpoint location,
the user
types either the G or P command. Thus, the G or P command can be used
without an argument, if program execution is to be resumed after a
breakpoint occurs.
If program execution is interrupted by the
occurrence of an error of the type BE, IO, EM, TR, or FP (see section
5.2), use of the G or P command causes execution to resume at the word
location following the error location,
rather than at the error
location itself.
The P command is illegal if a breakpoint has not yet occurred.
If
this
command is issued before a breakpoint location has been
encountered, ODT responds with a question mark
(?)
on the line in
error and prompts with the underline character (or back-arrow) on the
following line, indicating that the user must issue the G (Go) command
to begin or resume program execution.
If the task has not yet been run, the G command starts execution at
the program's entry-point
(transfer)
address;
otherwise,
the G
command causes program execution to resume immediately following the
last logical instruction executed.
In this case, the G command has
the same effect as the P command when resuming execution from a
breakpoint location.
When the G or P command is executed, the user general registers
(see
section 3.3)
are restored to their original (pre-breakpoint) values,
the BPT instructions are swapped with the user instructions referenced
by the breakpoint address registers, and control is returned to the
user program.
when a breakpoint is set within a loop, it may be desirable to allow
the program to execute through the loop a specified number of times
before recognizing the breakpoint.
This can be done through an
alternate form of the P command which takes an argument k, where k is
an octal integer specifying the number of times the breakpoint is to
be encountered before program execution is suspended.
If the P
command is issued without an argument, execution continues only to the
next breakpoint (or to the end of the program).

3-18

ODT COMMAND SEQUENCES AND FUNCTIONS
The breakpoint proceed count is associated only with that breakpoint
which has most recently occurred, i.e., a different proceed count is
associated with each breakpoint, determining the number of times each
breakpoint is to be encountered before program execution is suspended,
as shown in the example below:
3B:001010
_1250;5B
_7P

3B:OLJ1010

;EXECUTION IS HALTED AT BREAKPOINT 3.
;BREAKPOINT 5 IS SET AT LOCATION
;1250.
;EXECUTION IS CONTINUED, LOOPING
;THROUGH BREAKPOINT 3 SIX TIMES,
;HALTING ON THE 7TH OCCURRENCE OF THE
;BREAKPOINT.
;EXECUTION IS HALTED AT BREAKPOINT 3,
;ODT PRINTS BREAKPOINT MESSAGE AND
;AWAITS A COMMAND.

The breakpoint proceed counts can be inspected by typing a command
the form:

$nG/
where n represents the octal identifier for
the breakpoint proceed
count register
(see $nG, Table 3-1). After the slash (/) is typed,
ODT prints the contents of the specified register. The user may type
the <CR> key to close the location (leaving the count unchanged), or a
new count may be E~ntered through the command $nG/k <CR>, where k
represents the nE~W count to be entered. Still another alternative is
to type the <LF> key repetitively to examine the values in subsequent
(or all)
breakpoint proceed count registers. The following sequence
shows how the proceed counts are examined and changed:
_$UG/000001 15 <LF>
$1G /UOOOOl <LF>
$2G /UOOOOl <LF>
_3G /000005 <CR>

3.7

;PROCEED COUNT FOR BREAKPOINT 0 IS
;EXAMINED, MODIFIED TO 15, FOLLOWED
;BY LINE-FEED COMMAND.
;PROCEED COUNT FOR BREAKPOINT 1 IS
;EXAMINED, FOLLOWED BY LINE FEED
;COMMAND.
;PROCEED COUNT FOR BREAKPOINT 2 IS
;EXAMINED, FOLLOWED BY RETURN
;COMMAND.

SINGLE-INSTRUCTION MODE COMMANDS:

Sor nS

A command has been provided in ODT to allow the user to step through
the execution of the program one instruction at a time, if desired.
An alternate form of this command takes an argument, allowing the user
to specify the number of instructions to be executed before task
execution is again suspended.
When the single-instruction mode is in effect,
breakpoints are not
present in the user task. Rather, task execution is suspended as a
result of setting the T-bit in the Processor Status Word (see Appendix
A)
as the user instruction is executed. Thus, when executing the S
command without an argument, each user
instruction encountered is
trapped to suspend execution.
If the S command is being used with an
argument, however, the trap occurs, but ODT does not suspend task
execution until the specified instruction count has been completed, as
described in the following paragraphs.

3-19

ODT COMMAND SEQUENCES AND FUNCTIONS
The command for the single-instruction mode takes the form nS, where n
represents an octal integer specifying the number of user task
instructions to be executed before control is returned to ODT.
If n
is omitted, an argument of 1 is assumed. When the instruction count
(n) is completed, ODT suspends task execution and prints a message of
the form BB:a, where a represents the address of the next instruction
to be executed. The following sequence illustrates the use of this
command:
_7S
8B:001000

;SETS INSTRUCTION COUNT, ESTABLISHES
;SINGLE-INSTRUCTION MODE, AND
;INITIATES TASK EXECUTION.
;INDICATES THAT INSTRUCTION COUNT HAS
;BEEN COMPLETED, TYPES OUT ADDRESS OF
;NEXT INSTRUCTION TO BE EXECUTED.

If ODT is currently representing task addresses relative to a
relocation register, note (for reasons stated in section 3.1) that the
terminal message for single instruction mode takes the form BB:n,a.
The value n represents the octal register specifier indicating the
:relocation register whose contents are closest in value to the address
of the last instruction executed,
and the value a represents the
6-digit octal address which must be added to the contents of
relocation register n
(i.e.,
the relocation bias of the module in
question) to determine the actual relocated address of the location
being displayed.
The following command sequence illustrates this
principle:
_101200;1R
_l,1052;B
_G
OB:l,001052

_s
BB : 1 , 0010 5 6

_s
BB:l,001062

;SETS RELOCATION REGISTER 1
;TO THE VALUE 101200.
;SETS BREAKPOINT 0 RELATIVE
;TO CURRENT VALUE OF
;RELOCATION REGISTER 1.
;SETS BREAKPOINT IN TASK AND
;INITIATES TASK EXECUTION.
;BREAKPOINT 0 OCCURS.
;INITIATES SINGLE-INSTRUCTION MODE.
;ADDRESSES OF NEXT INSTRUCTION
;TO BE EXECUTED ARE REPRESENTED
;AS VALUES WHICH MUST BE BIASED BY
;CONTENTS OF RELOCATION REGISTER 1.

In the example above, to determine the relocated address of the next
instruction to be executed,
the user must add the values 1056 and
1062, respectively, to the relocation bias 101200 in relocation
register 1, thus yielding relocated address values of 102256(8) and
102262 ( 8).

3.8

SEARCH OPERATIONS

All or any specified portion of memory within the task's partition can
be searched for word or byte locations which contain specific bit
patterns. A second type of search can also be initiated which
examines memory locations for words which reference a specified
location in the user task.
The following sections describe these
search operations.
(See also Appendix B, Search Algorithms.)

3-20

ODT COMMAND SEQUENCES AND FUNCTIONS
3.8.1

Word/Byte Search Commands:

w, kW, miw, or mikW

Before initiating a word search,
several preconditions must be
established:
(1)
the search limits must be defined;
(2) the search
mask must be established;
and (3) the search argument itself must be
specified.
The search limits are defined through address values entered into the
low memory limit regsiter
($L)
and the high memory limit register
($H), as noted in Table 3-1.
If, after opening the low memory limit
register with the $L/ command, the current 6-digit octal value being
displayed is not desired, the user may enter any new value appropriate
to the
intended search operation. The desired address value in the
high memory limit register may be established in like fashion after
first opening the register with the $H/ command.
As reflected in the command forms below, either
absolute
relocatable task addresses can be set in the $L and $H registers:
$L/000000 1000
$L/000000 1,1000

;SETS $L TO ABSOLUTE ADDRESS.
;SETS $L TO RELOCATABLE ADDRESS.

$H/000000 2000
$H/000000 0,2000

;SETS $H TO ABSOLUTE ADDRESS.
;SETS $H TO RELOCATABLE ADDRESS.

·~

When relocatable address values are specified in the search limit
registers,
the apparent values in $L and $H are effectively augmented
by the value of the relocation bias for the object module.
The search mask is specified in the search mask register
($M).
The
command which accomplishes this action is described under $M in Table
3-1. Bits set to 1 in the mask define corresponding bit positions in
the search argument (see below) and the memory words (or bytes) which
will be compared during the search operation;
bits not set to 1 in
the mask cause the corresponding bit positions in the search argument
and the memory words (or bytes) being searched to be ignored
in all
compare operations.
The search argument is specified in the search argument register ($A).
The command which accomplishes this action is also described in Table
3-1 under $A. Note that either a word or byte search argument value
can be specified.
The discrete actions described above
establish
the
necessary
preconditions for
initiating search operations. These actions are
reflected in the first four lines of the ODT command sequence in the
example.
At this point,
the user need only type the W command in
order to initiate the search, as shown in the fifth line of the
example.
If a desired mask already exists, however,
as a residual parameter
from a previous search operation or as the result of an overt action
in preparing for a new search operation, the user may initiate the
search through a command of the following form:
kW
where k represents the desired search argument.
In using this command
form,
note that the value preceding the W command is taken by ODT as
the search argument, not the search mask.

3-21

ODT COMMAND SEQUENCES AND FUNCTIONS

On the other hand, if a desired search argument already exists as a
result of the actions noted above, the user may initiate the search
operation through a command of the following form:

m;W
where m represents the desired search mask.
A more convenient method of initiating search operations, however,
is
to specify the search mask and the search argument as part of a
multi-element ODT command.
Assuming that the search limits have
already been specified in the $L and $H registers (as described
above), the user may simply type a command in the following form:
m; kW

where m represents the search mask ($M), and k represents the search
argument
($A).
Typing W then initiates the search operation without
further
intervention.
When a match
occurs,
i.e.,
when
the
corresponding bit positions in the search argument and the memory word
being compared agree under the specified mask, ODT prints the address
of the matching location and its contents.
The search operation is conducted in either
depending on the mode of the last open command.

word

byte

mode,

In the search process, an exclusive OR (XOR)
is performed with the
word
(or byte) currently being examined and the search argument. The
result of this comparison is then ANDed with the specified search
mask.
If the result is zero, a match occurs. ODT then types the
address and the contents of the matching location, as shown throughout
the example below.
The following command sequences illustrate both word and
operations:
_$M/177777
_$L/OOOOOO
_$H/OOOOOO
_$A/000000

177400 <CR>
1000 <CR>
1400 <CR>
600 <CR>

001010 /000770
001034 /000404
_377 ;W
001020 /000200
_213W
001032 /000213
_$A\213 200 <CR>
_SW

byte

;SET MASK TO TEST HIGH-ORDER BYTE.
;SET LOW LIMIT SEARCH ADDRESS.
;SET HIGH LIMIT SEARCH ADDRESS.
;SET WORD SEARCH ARGUMENT TO 600.
;INITIATE WORD SEARCH OPERATION.
;PRINT ADDRESS AND MATCHING WORD.
;PRINT ADDRESS AND MATCHING WORD.
;CHANGE MASK TO TEST LOW-ORDER
;BYTE AND INITIATE SEARCH.
;PRINT ADDRESS AND MATCHING WORD.
;CHANGE SEARCH ARGUMENT TO 213 AND
;INITIATE SEARCH.
;PRINT ADDRESS AND MATCHING WORD.
;SET BYTE SEARCH ARGUMENT TO 200.
;CHANGE BYTE SEARCH ARGUMENT TO 5 AND
;INITIATE SEARCH.

If the user specifies a mask having zeros throughout,
locations within the search limits are printed by ODT.

all

The word/byte search algorithm
Appendix B.

detail

described

3-22

further

memory
in

ODT COMMAND SEQUENCES AND FUNCTIONS
3.8.2

Not This Word/Byte Search Commands:

N, kN, m;N, or m;kN

This search works exactly the same as the word search described above,
except that words (or bytes) which do not match are printed. Thus, a
test for inequality is performed on all memory words/bytes in the
specified search range.

3.8.3

Effective Address Search Commands:

E, kE, m;E, or m;kE

ODT also searches for memory locations containing instructions which,
when executed, effectively result in a reference to a specified task
address. After first defining the search limits in the $L and $H
registers,
as described in section 3.8.l above, the effective address
search may be initiated by typing the following command:
m;kE
where m represents the search mask, and k represents the search
argument.
The values m and k are entered automatically in the search
mask register
($M)
and
the
search
argument
register
($A),
respectively, when the m;kE command is issued.
As is the case with word/byte search operations described in sections
3.8.l and 3.8.2, the command forms used to initiate an effective
address search depend on which of the required ODT internal register
values currently exist.
For example, if the required register values
are specified in discrete steps, as shown in the first four lines of
the command sequences below,
the effective address search can be
initiated by typing only the E command.
If the desired search mask
value exists, however,
as the result of prior action, the command
form:
kE
suffices to initiate search operations, where k represents the search
argument.
If,
on the other hand, the desired search argument exists
as a result of prior action, the command form:
m;E
may be used to initiate the search,
mask.

where

In an effective address search,
printed by ODT:

following

the

represents
types

Words which contain an absolute
argument itself);

address

Words which contain a relative address
the specified search argument address;

Words which contain a relative branch
specified search argument address.

(i.e.,
off set
and

the

words
the

reference

are

to
the

Note that since references to k,
an effective address,
are being
searched for,
normal usage of this command requires that the mask
register be set to 177777; otherwise, the effective address will be
modified.

3-23

ODT COMMAND SEQUENCES AND FUNCTIONS
The command sequences and ODT responses in an effective address search
are illustrated in the example below:
_$M/000000
_$L/OOOOOO
_$H/OOOOOO
_$A/000000

177777 <CR>
400 <CR>
100400 <CR>
1034 <CR>

_E
001016 /001006
001054 /002767
_1020E
001022 /177774
001030 /001020

;SET MASK TO COMPARE ALL BITS.
;SET LOW LIMIT SEARCH ADDRESS.
;SET HIGH LIMIT SEARCH ADDRESS.
;SET EFFECTIVE ADDRESS SEARCH
;ARGUMENT TO 1034.
;INITIATE EFFECTIVE ADDRESS SEARCH
;OPERATION.
;PRINT RELATIVE BR~NCH LOCATION AND
;CONTENTS.
;PRINT RELATIVE BRANCH LOCATION AND
;CONTENTS.
;INITIATE A NEW SEARCH FOR REFERENCES
;TO LOCATION 1020.
;PRINT RELATIVE ADDRESS OFFSET
;LOCATION AND CONTENTS.
;PRINT LOCATION CONTAINING ABSOLUTE
;ADDRESS 1020.

Particular attention should be given to the reported references to the
effective address,
because a word may have the specified bit pattern
of an effective address without actually being referenced in the
program.
ODT reports all occurrences of a possible effective address
reference.

3.9

FILL COMMANDS:

F or kF

~rhe

search argument register (see $A, Table
3-1)
can be used
in
conjunction with the F command to set a block of memory to a specified
value.
While the most
commonly-used
value
is
zero,
other
possibilities are +l, -1, ASCII space, etc.
Before a block of memory
can be initialized to a given value, the limits of the memory area to
be filled must be defined through the low memory limit register ($L)
and the high memory limit register ($H).
Consult table 3-1 for
a
description of the commands which store address values in these
registers.
The initialization value may be stored in the search argument register
(see $A, Table 3-1)
as a discrete step.
It is more convenient,
however, to specify this value in the initialization command itself,
which takes the following form:
kF
This command automatically stores the initialization value k in the
search argument register ($A) and initiates the fill operation.
ODT
then stores this value into successive memory words or bytes, starting
at the address specified in the low memory limit register ($L) and
ending with the address specified in the high memory limit
register
( $H) •
The initialization command fills the specified memory range with words
if the last open command was performed in word mode;
correspondingly,
the specified memory range is filled with byte values if the last open
command was performed in byte mode.

3-24

ODT COMMAND SEQUENCES AND FUNCTIONS
For the examples below, assume that the
contain the following values:

listed

relocation

registers

Relocation register 1 = 1000
Relocation register 2

2000

Relocation register 3

3000

The command sequences below might then occur.
The first fill
operation sets word locations 1000 _through 1776 to zeros (0), while
the second operation sets byte locations 2000 through 2777 to ASCII
spaces.
_$L/OOOOOO 1,0 <CR>
_$H/OOOOOO 2,-2 <CR>
_$A/123456 0 <CR>
_F

;SET LOW MEMORY LIMIT TO 1000.
;SET UPPER MEMORY LIMIT TO 1776.
;SET SEARCH ARGUMENT REGISTER TO 0.
;FILL SPECIFIED MEMORY BLOCK WITH
;ZEROS.

_$L/001000 2,0 <CR>
_$H/001776 3,-1 <CR>
_$A\OOO 40 <CR>

;CHANGE LOW MEMORY LIMIT TO 2000.
;CHANGE UPPER MEMORY LIMIT TO 2777.
;OPEN SEARCH ARGUMENT REGISTER IN
;BYTE MODE AND CHANGE ITS CONTENTS TO
;OCTAL 40 (ASCII SPACE) •
;FILL BYTES IN SPECIFIED MEMORY BLOCK
;WITH SPACES.

In a fill operation, the memory limits must be defined through
discrete actions which deposit the desired address values in the low
memory limit register ($L) and the high memory limit register
($H).
The only argument that can be specified as an element of the fill
command is the fill value itself. When so specified, this fill value
establishes the initial contents of the search argument register ($A)
or modifies its current contents before initiating the fill operation.
If the fill value~ is not specified when the F command is issued, ODT
takes the current contents of $A in performing the fill operation.

3.10

OFFSET CALCULATION COMMANDS:

aO or a;kO

Relative addressing and branching involve the use of an offset,
i.e.,
the
number
of
words or bytes forward or backward from the
currently-open location to the effective address. During a debugging
session,
it may be desirable to change a relative address or branch
reference by replacing an existing instruction offset with another
value.
ODT calculates and prints instruction offsets in response to
the commands described below.
The aO command causes ODT to calculate and print the PC-relative
offset and the branch displacement from the currently-open location to
a specified address. Thus, the aO command is equivalent in function
to the command .;kO, where the dot (.) represents the currently-open
location (see section 3.16.1), and k represents the specified address.
The following sequences illustrate the use of the aO command:
_16126/001402 161340 _000004 >000002 <CR>
_1034/103421 10460 _000010 >000004 <CR>

3-25

ODT COMMAND SEQUENCES AND FUNCTIONS

In using the aO command form, it is assumed that a location is already
open, as shown in the example above. Thus, the user need only specify.
the desired address to be used in calculating the offsets from the
current location.
After typing the O character, ODT calculates the
offsets and prints the results on the same line.
The PC-relative
offset is flagged with the underline (_) or back-arrow character, and
the branch displacement is flagged with the right angle-bracket
(>)
character.
The a;kO command causes ODT to calculate· and print the PC-relative
offset and the branch displacement from one specified address to
another.
In this command form, the symbol a represents the first
address, and k represents the second address.
The following sequences illustrate the use of this command form:
_16126;161340 _000004 >000002 <CR>
_1034/103421 1022;10340 _000010 >000004 <CR>
_1022;10340 _000010 >000004 <CR>
In the first line of the examples above, the first address (16126)
is
specified, followed by a semicolon (;) and the second address (16134).
After typing the O character, ODT calculates the offsets and prints
them in the same manner as in the aO command above. The remaining
examples follow this same pattern.
Note in the command form a;kO that it need not be issued in connection
with an open location.
Since both address values are explicitly
specified, the address of the currently-open location has no implied
effect in the calculation of the offset values. The second and third
examples above illustrate this principle.
The command form a;kO is also useful in
values, as shown below.

calculating

negative

offset

_1022;10340 000010 >000004 <CR>
_1034;10220 -177764 >177772 <CR>
The first example calculates a positive offset value, while the second
sequence calculates a negative value.
It is often desirable to know
the PC-relative offset and the branch displacement values from a
higher
memory
address to a lower memory address,
since many
instructions in the normal flow of program logic result in a transfer
of control in the negative direction.
In either command form (aO or a;kO), note that the location for which
offsets have been calculated remains open for further operations.
For
example, if the user wants to change the offset value in the low-order
byte of the instruction word, he may do so as shown in the following
sequence:
_1034/103421 11320 _000074 >036 1034\021 36 <CR>
_/103436
Note that location 1034 is first opened in word mode.
If,
after
calculating the offsets, the user desires to change the value of the
low-order byte, byte mode must first be established for that location;
the command 1034\, as shown in the example above, is essential to this
purpose.
Unless byte mode is established for the current location,

3-26

ODT COMMAND SEQUENCES AND FUNCTIONS

any value then entered is interpreted as a word value. The net result
in that case is the obliteration of the instruction op-code in the
high-order byte.
If the user wishes to verify the alteration of the offset value, he
may do so by typing the slash (/) command on the succeeding line, as
shown above.

3.11

RELOCATION RI~GISTER COMMANDS:

a;nR, a;R, nR, or R

The function of the relocation registers is described in section 1.2.3
and in Table 3-1.
At the beginning of a debugging session, these
registers are preset to the relocation biases of the relocatable
modules of interest during the debugging session.

'"-"

Relocation registers are initialized to -1 (octal 177777, the highest
possible memory address), so that unwanted registers do not enter into
the selection process when ODT searches for the most appropriate
relocation register for its address calculations. When relocation
registers are set to -1, all task image addresses reference either
absolute physical memory locations (for non-mapped systems) or virtual
memory locations (for mapped systems).
A relocation register is set by typing the desired bias value,
followed by a semicolon and the specification of one of the eight
relocation registers, as shown below:
a;nR
The symbol a represents an address expression,
integer from 0 through 7.

and

represents

The following command form may also be used:
a;R
In this case, relocation register 0 is assumed to be specified, since
the register specifier has been omitted. In contrast to the command
form a;B for the br,=akpoint address registers described in section
3.5, however, the repetitive execution of the command form a;R does
not enter values serially into the relocation registers.
Therefore,
the command form a;nR must be used to enter a bias value into a
specific relocation register other than register 0.
To set all relocation registers to -1, the following command is typed:
R

;SETS ALL RELOCATION REGISTERS
; TO -1 , 1 7 7 77 7 ( 8 ) •

To set a specified relocation register to -1, a command in the form nR
is used, where n represents an octal register specifier, as shown
below:
_3R

;SETS ONLY RELOCATION REGISTER 3 TO
;-1, 177777(8).

3-27

ODT COMMAND SEQUENCES AND FUNCTIONS

To set a specified relocation register to a desired value,
a command
in the form a;nR is used, where a represents the desired value, and n
represents the octal register specifier, as shown below:
1000;5R
=5,100;5R

;SETS RELOCATION REGISTER 5 TO 1000.
;EFFECTIVELY ADDS 100 TO THE CONTENTS
;OF RELOCATION REGISTER 5.

Position-independent code may be loaded into address space other than
that to which it was linked. When a program is loaded into address
space below that at which it was linked, the appropriate relocation
bias is the 2's complement of the apparent downward displacement. One
method for easily evaluating this bias and storing it in th€
relocation register is illustrated below.
Assume, for example, that the program was linked to location 5000 and
then moved downward to location 1000. The following command sequence
would then be used:
lOOO;lR
=l,-5000;1R

;SETS RELOCATION REGISTER 1 TO 1000.
;CHANGES RELOCATION BIAS TO ACTUAL
;DOWNWARD DISPLACEMENT.

The last command above stores the 2's complement of 4000 in relocation
register 1, as desired.
An alternate method of establishing the downward displacement might be
the following command sequence:
_$0R/177777 1000-5000 <CR> ;OPENS RELOCATION REGISTER 0 AND
;SETS RELOCATION BIAS TO ACTUAL
;DOWNWARD DISPLACEMENT.
_/174000
;SLASH COMMAND PRINTS RELOCATION
;BIAS IN PREVIOUSLY-OPENED LOCATION.
ODT maintains a table of relocation register locations, beginning with
$OR. These locations may be opened through a command of the following
:Eorm:
_$nR/
The symbol n represents an octal digit specifying which one of the
eight locations is to be opened. Such locations may be opened and
modified in the same manner as any other register location, as shown
in the following sequence:
_$3R/001000 <LF>
$4R /002000 <LF>
$5R /004000 <CR>
_$3R/001000 1040 <CR>
_6000;6R

;RELOCATION REGISTER 3 IS OPENED.
;THE <LF> COMMAND OPENS RELOCATION
;REGISTER 4. A SECOND <LF> COMMAND
;OPENS RELOCATION REGISTER 5. THE
;<CR> COMMAND ENDS SEQUENCE.
;OPENS RELOCATION REGISTER 3 AND
;CHANGES ITS CONTENTS TO 1040.
;SETS RELOCATION REGIST~R 6 TO 6000
;AND ENDS SEQUENCE.

3-28

ODT COMMAND SEQUENCES AND FUNCTIONS
RELOCATION CALCULATOR COMMANDS:

3.12

a1nK, nK, or K

When a location has been opened, it is often desirable to associate
the relocated address of that location with its relocatable value.
To calculate the relocatable address of a given location relative to a
particular relocation bias, the user types a command in the following
form:
a;nK
The symbol a represents the relocated address
relocatable address is to be calculated,
relocation register specifier (0 through 7).

value from which
and n represents

the
the

The K command is effective in conjunction with opened word and byte
locations.
For example,
if the command elements a and
are not
specified, the currently-open location is assumed to be operative
(i.e.,
.,
is assumed).
Thus,
the command 3K is equivalent in
function to the command .;3K (see section 3.16.1).
If the relocation register specifier n is omitted,
the relocation
register whose contents are equal to, or closest to (but less than)
the currently-open location is automatically selected by ODT for use
in calculating the relocatable address.
In the example below,
relocation register. 2, which contains 2000, meets this requirement:

_2500;K

2y000500

;CALCULATES RELOCATABLE ADDRESS.

Thus, ODT's response to the K command consists of the octal identifier
(2)
of the relocation register used in the calculation, followed by
the relocatable address value
(000500)
of the specified relocated
address (2500).

A number of command forms are available for listing a block of memory
locations within the user task's partition. The particular command
form used in initiating a listing operation depends on whether the
required ODT register values exist as the result of prior action or
whether they must be specified overtly as an argument in the listing
command itself.
In either case, the following ODT registers must
contain the user-specified values required for the intended listing
operation:
1.

The beginning address of the memory range to be printed must
be deposited in the low memory limit register (see $L, Table
3-1) •

The ending address of the memory range to be printed must be
deposited in the high memory limit register (see $H, Table
3-1) •

The logical unit number of the listing device must be
deposited in the device control LUN register (see $nD, Table
3-1). The appropriate values for the device control LUN
registers are normally established by the Task Builder.
Therefore, the user need not be concerned with any explicit
ODT operations in establishing or altering these values. The

3-29

ODT COMMAND SEQUENCES AND FUNCTIONS

default values for these registers are described in detail in
Table 3-1.
Normally, device control LUN register 0 ($OD)
contains the logical unit number of the user terminal device
(TI:), while device control LUN register 1 ($1D) contains the
logical unit number of the console listing device (CL:).
Assuming that the necessary register values described above exist as
the result of prior action,
the user need only type the L key to
initiate a listing operation:

;PRINTS MEMORY LOCATIONS WITHIN
;SPECIFIED ADDRESS LIMITS USING
;CONSOLE LISTING DEVICE (CL:).

If the desired address value presently exists in the low memory limit
register
($L)
and the user wishes either to establish the required
value for the high memory limit register ($H) or to modify its current
contents, the following command form is used:
_kL

;TAKES ADDRESS VALUE "k" AS ENDING
;LOCATION AND INITIATES LISTING
;OPERATION.

Conversely, if the desired address value presently exists in the high
memory limit register ($H) and the user wishes either to establish the
required value for the low memory limit register ($L) or to modify its
current contents, the following command form is used:
- a·L
,

;TAKES ADDRESS VALUE "a" AS
;BEGINNING LOCATION AND INITIATES
;LISTING OPERATION.

If neither of the required address values presently exist
$H, the following command form is used:
_a;kL

and

;TAKES ADDRESS VALUES "a" AND "k"
;AS THE BEGINNING AND ENDING
;ADDRESSES, RESPECTIVELY, AND
;INITIATES THE LISTING OPERATION.

Finally, a fourth command form is used if none of the required values
presently exist.
In this case, all the discrete values required for a
listing operation must be specified as arguments in the listing
command itself, as shown below:
_n;a;kL

;ALL LISTING CONTROL ARGUMENTS
;ARE SPECIFIED IN SINGLE
;LISTING COMMAND.

The command form above uses the logical unit number contained in the
specified device control LUN register n ($nD) to print all memory
locations within the specified address Limits a and k. Any value for
n other than zero
(0)
or one (1) is treated by ODT as though the
console listing device ($1D) was specified, i.e.,
the default value
for n is one (1).
The address values a and k specified as arguments in the listing
command may be either absolute or relocatable in form.
It is
advisable, however, when debugging relocatable program segments,
to
use relocatable address expressions in defining the memory limits in
$L and $H for listing operations. By so doing,
the task addresses

3-30

ODT COMMAND SEQUENCES AND FUNCTIONS
printed out by ODT during the listing of the specified memory block
can be associated directly with the relocatable addresses in the
assembly listing.
Any address values so specified, whether absolute
or relocatable, cause corresponding values to be entered into the
memory limit registers when the L command is executed. The use of
relocatable address values, however,
assumes that an appropriate
relocation bias for the object module in question has been established
in one of the eight available relocation registers.
For example,
if
an object module has a relocation bias of 370(8), the following
command sequence might be used in initiating a listing operation:
_0,370;R <CR>
_0,1020;0,J.040L

;SETS RELOCATION REGISTER 0 TO
;RELOCATION BIAS FOR DEBUGGING THE
;MODULE.
;INITIATES THE LISTING OF THE MEMORY
;BLOCK BETWEEN RELOCATABLE TASK
;ADDRESSES 1020 AND 1040.

The beginning address in the resulting listing will
then
be
represented in rE!locatable form, i.e., 0,001020, as will the ending
address.
~

In listing a block of memory, it is important to note that the listing
format is governed by the mode of the previous open command.
In other
words, the interpretation of each memory location and the format of
the listing output are determined by the last output mode used by ODT.
In this connection, two general output listing modes are available, as
described below:
1.

Word mode octal.
Established through opening a word location
through the slash (/) command (see section 3.2.3) or any other
command which opens a location and causes its entire 6-digit
octal value to be printed.

Byte mode octal. Established through opening a byte location
through the backslash (\) command (see section 3.2.3) or any
other command which opens a byte location and causes its
3-digit octal value to be printed.

A sequence of operations which results in the printout
and byte locations is shown in Figure 3-1.

Three other listing options are available to
establishing alternate modes, as described below:

user

the

both

word

through

Word mode ASCII.
Established through
interpreting
the
contents of a location using the double-quote (") character
before issuing the listing command.
For
example,
the
representative expression 0,1020",
as shown in Figure 3-1,
establishes word mode ASCII before the listing operation is
initiated.

Byte mode ASCII.
Established through
interpreting
the
contents of a location using the single-quote (') character
before issuing the listing command. As shown in Figure 3-1,
the representative expression 0,1020' establishes byte mode
ASCII before the listing command is issued.

Word mode Radix-50.
Established through interpreting the
contents of a location using the percent sign (%) before
issuing the listing command. This listing option is invoked
through the representative expression 0,1020%, as shown in
Figure 3-1.

3-31

ODT COMMAND SEQUENCES AND FUNCTIONS

Note that the address expressions referenced in Items 1 through 3
above are intended to be illustrative only. Any means of establishing
the desired output mode before issuing the listing command is
permissible.
In all cases of ODT listing output, the first line starts with the
beginning octal address of the memory block being printed, followed by
the contents of eight consecutive word or byte locations.
Subsequent
lines consist of the beginning octal address of the next eight
consecutive locations, etc.
>PRE
ODT: ... PRE
_110400; I':
_$L/000000 0. 0452e:
_$H/00000E1 0. E146n

_L
0. 004522 /020105 Et E1 E1 EHH1 (1(1(1(10(1 0200(1(1 E147H11 (12(11(14 (154524 (14252(1
0. 004542 /04144(1 E151H11 (142522 &.n7124 €146451 (152517 (152116 (14444(1
0. 004562 /050116 (152125 (15 3:€14 0 046117 0465~:5 (1~:(11(15 0(100(10 (1(1(1(1(1(1
0, 004602 /020000 (1471(11 (12(11(14 054524 (14252£1 ~H144(1 (1511€11 042522
0, 004622 /037124
_0. 04522\105 L
0.004522 \105 04Et (t(t(t (1(1(1 (1(1 (1 0(1(1 (100 ei 4 (1
0.004532 \101 116 104 (14(1 124 13:1 12(1 105
0·004542 \040 103 101 122 122 1€15 124 076
0 . 004552 \051 115 117 H5 1 U: 124 (140 111
0. 004562 \116 12€1 125 124 (14(1 126 117 114
0, 004572 \125 115 105 (14(1 (1(1(1 0(1(1 0(10 (10(1
0.004602 \000 04(1 H11 116 1(14 (140 124 13: 1
0,004612 \120 Ht5 £t4Et 1(13 Ht1 122 122 105
0.004622 \124
_0, 04522·· E L
0,004522 ,. E
0, 004532 I A N D
T ~· F' E
0.004542
c: A R I': E T )
o. 004552 i ) M (I LI N T
I
0. 004562 ,. N p u T
v (I L
0. 004572 I LI M E
,.
0. 004602
A N D
T ~·
0.004612 ,. F' E
c: A I': I': E
0, 004622 ,. T
_0, 04522"E
0.004522 II E
AN [)
T~' PE
EL 084542 fl c A~: RE T> ) fil C1U NT
0. 004562 "NF' LIT
v OL LIM E
(: Al': l':E
o. 004602 II
AH D Tl' F' E:
0. 004622 II T >
_0, 04522:{EFLI l
0.004522 :·!EFU
EC:i2 LB EFT NK. KO:
0. 004542 i!J /X MFG! KC:Z IE: 6 Lt13 MY9 MS~' IC
0. 004562 ;.~us MS/ M1H LHO LN7 EFU
0. 004602 ;.~E D2 L T3: EFT NK. KC:li<: J /)<: MFG! KC:Z
0, 004622 ;.~I 8 6

Figure 3-1

ODT Listing Modes and Formats

3-32

~.'

ODT COMMAND SEQUENCES AND FUNCTIONS
3.14

REPRINTING OPEN LOCATIONS

It is often desirable to print the contents of an open location in a
mode other than that in which it was opened or to print its contents
in other than 6-digit octal format.
The commands described below, all
of which cause the word or byte value to be stored in the quantity
register ($Q) when printed, are available for this purpose.
An important operational characteristic of ODT should be noted in
connection with the use of the interpretive commands described below
and the <LF> command. As pointed out in section 3.13, ODT has five
distinct output modes:

'-'1

(/)

Word

modE~

octal

Byte

modE~

octal (\)

Word modE! ASCII

( II )

Byte mode ASCII

( I )

Word mode! Radix-50

When a location is opened in any one of these output modes, ODT
"remembers"
(saves) the mode of the location just opened/interpreted.
Although the user may then issue any other interpretive command(s)
on
the same line,
when the
<LF> command is entered to close that
location, ODT opens the next sequential location in the mode of the
previous location.
In other words,
after a location is opened or
interpreted, the output mode thus established, prevails for
all
subsequent <LF> commands.
The following command sequences illustrate
this principle:
_0,234\346 'F <LF>

000235 \025 <LF>
000236 \100 <CR>

........,,

(%)

1000"AB

I ,A,

<LF>

001002 "CD <LF>
001004 "EF <CR>

;RELOCATABLE LOCATION 234 OPENED IN
;BYTE MODE OCTAL AND INTERPRETED IN
;BYTE MODE ASCII, FOLLOWED BY <LF>
;COMMAND.
;NEXT SEQUENTIAL LOCATION OPENED
;IN BYTE MODE.
;SAME AS ABOVE.
;CONTENTS OF LOCATION 1000 INTERPRETED
;IN WORD MODE ASCII AND BYTE MODE
;ASCII, FOLLOWED BY <LF> COMMAND.
;NEXT SEQUENTIAL LOCATION INTERPRETED
;IN WORD MODE ASCII.
;SAME AS ABOVE.

_0,232/034567 'W "W9 %IG1 <LF> ;RELOCATABLE LOCATION 236
;OPENED IN WORD MODE OCTAL AND
;INTERPRETED IN BYTE MODE ASCII, WORD
;MODE ASCII, AND WORD MODE RADIX-50,
;FOLLOWED BY <LF> COMMAND.
0,000234 /000624 <LF>
;NEXT SEQUENTIAL LOCATION OPENED IN
;WORD MODE OCTAL.
0,000236 /000100 <CR>
;SAME AS ABOVE.

3-33

ODT COMMAND SEQUENCES AND FUNCTIONS
Although the examples above are general in nature and do not
illustrate the use of all the output modes,
the principle so
demonstrated applies to all the interpretive commands described in
sections 3.14.1 through 3.14.4. For convenience, these examples are
presented in this section, rather than being repeated in context with
the discussions below.

3.14.1

Print Octal Byte Value:

Typing the backslash (\) command when a word location is currently
open causes ODT to interpret and print the low-order byte of the word
as three octal digits, as shown below:
_0,20/044520 \120

;PRINTS LOW-ORDER BYTE IN
;CURRENTLY-OPEN WORD LOCATION.

Typing the backslash command when a byte location is currently open
causes ODT to reprint the contents of the byte location; as shown
below:
_0,23\021 \021

;REPRINTS VALUE OF BYTE LOCATION.

Typing the backslash command when a location is not open causes ODT to
print the byte value of the last-opened location, as shown below:
_0,234/000247 123456 <CR>
_\056
;PRINTS LOW-ORDER BYTE OF
;PREVIOUSLY-OPENED WORD LOCATION.
_0,237\041 <CR>
_\041

3 .. 14.2

;REPRINTS VALUE OF PREVIOUSLY;OPENED BYTE LOCATION.

Print Byte Mode ASCII Character:

' or a'

Typing the single-quote character
(')
when a word location is
currently open causes ODT to interpret and print the low-order byte of
the location as one ASCII character, as shown below:
-~'232/034567

;PRINTS THE CONTENTS OF THE OPEN WORD
;LOCATION AS ONE ASCII CHARACTER.

Typing the single-quote character when a byte location is open causes
ODT to interpret and print the byte value as one ASCII character, as
shown in the examples below:

__ or 232\16 7 I W
__ 0 r 1 Q 2 0 \ 3 2 3 I $
__u I 2 3 3 \ Q7 1 I 9
When the single-quote character is preceded by an address expression,
ODT uses the expression as an argument in determining the location to
be interpreted and printed, as shown below:
0,232'W

;INTERPRETS REFERENCED LOCATION AS
;ONE ASCII CHARACTER.

3-34

ODT COMMAND SEQUENCES AND FUNCTIONS
If no location is currently open when the single-quote command is
issued,
the previously-opened location is interpreted and printed, as
shown in the following sequence:
_0,232/034567 <CR>

_'W

3.14.3

;INTERPRETS PREVIOUSLY-OPENED WORD
;LOCATION AS ONE ASCII CHARACTER.

Print Word Mode ASCII Characters:

" or a"

Typing the double-quote character
(")
when a word location is
currently open causes ODT to interpret and print the contents of the
location as two ASCII characters, as indicated below:
_U,232/034567 "W9

;PRINTS THE CONTENTS OF THE OPEN WORD
;LOCATION AS TWO ASCII CHARACTERS.

If the double-quote character is preceded by an address expression,
ODT takes the expression as an argument in determining the location to
be interpreted and printed, as shown below:
_0,232"W9

;INTERPRETS REFERENCED LOCATION AS
;TWO ASCII CHARACTERS.

If no location is currently-open when the double-quote command is
issued,
the previously-opened location is interpreted and printed, as
reflected below:
_0,232/034567 <CR>
_'.'W9

;INTERPRETS PREVIOUSLY-OPENED WORD
;LOCATION AS TWO ASCII CHARACTERS.

Note that the double-quote command is effective only when issued in
connection with task locations which fall on even (word-boundary)
addresses, as shown below:
_0,232/034567 W9 <CR>
_0,232\167 "W9 <CR>

;INTERPRETS ENTIRE WORD VALUE.
;ALSO INTERPRETS ENTIRE WORD.

In contrast, however, issuing the double-quote command in connection
with an odd address (byte) location, although legal, merely causes the
3-digit octal byte value to be reprinted,
as reflected in the
following sequence:
0,233\071 "U71 <LF>
5,000234 \346 "F <LF>
0,000235 \025 "025

;REPRINTS ODD BYTE VALUE.
;INTERPRETS WORD LOCATION NORMALLY.
;REPRINTS ODD BYTE VALUE.

Note, in the second line above, that the word location relocatable 234
is interpreted normally in its entirety, even though the location is
currently open in byte mode. This example underscores the usefulness
of the double-quote character only in connection with word-boundary
locations.

3-35

ODT COMMAND SEQUENCES AND FUNCTIONS
3.14.4

Print Word Mode Radix-SO Characters:

% or a%

Typing the percent sign (%} when a word location is open causes ODT to
interpret and print the contents of the location as three Radix-50
characters, as shown below:
_0,232/034567 %IG1

;PRINTS THE CONTENTS OF THE OPEN WORD
;LOCATION AS THREE RADIX-50
;CHARACTERS.

If the percent sign is preceded by an address expression
(a}, ODT
evaluates the expression to determine the location to be interpreted
and printed, as shown below:
_.O , 2 3 2%IG1

;INTERPRETS REFERENCED LOCATION AS
;THREE RADIX-50 CHARACTERS.

As with the preceding single-quote and double-quote interpretive
commands,
typing the percent sign when no location is currently open
causes ODT to print the contents of the previously-opened location in
Radix-50 form, as shown below:
_0,232/034567 <CR>
_%IG1

;INTERPRETS PREVIOUSLY-OPENED
;LOCATION AS THREE RADIX-50
;CHARACTERS.

Also, the percent sign is effective only when issued in connection
with an even address location, even though a word-boundary location
may be currently open in byte mode, as shown below:
0,242/001542 % UZ <CR>
=0,242\142 % UZ <CR>

;INTERPRETS ENTIRE WORD VALUE.
;ALSO INTERPRETS ENTIRE WORD.

Using the percent sign in connection with an odd address value has the
same effect as that described above for the double-quote character, as
indicated below:
_0,241\025 %025 <LF>
0,000242 \142 % UZ <LF>
0,000243 \003 %003

3.15

;REPRINTS ODD BYTE VALUE.
;INTERPRETS WORD LOCATION NORMALLY.
:REPRINTS ODD BYTE VALUE.

INTERPRETING EXPRESSION VALUES:

The equal sign (=} enables the user to interpret expression values,
address values,
and a variety of other expression forms involving
arithmetic operations. The use of this command implies that
it is
preceded by the entry of one or more characters constituting a legal
ODT expression.
This command cannot be used to interpret the currently-open location
or the last previously-opened location. A character sequence must be
entered overtly prior to issuing the = command:
otherwise, ODT prints
out a string of six octal zeros (000000).
As shown in the examples below, this command causes any expression
value which precedes it to be converted to a 6-digit octal value.
In
addition, the word so printed is stored in the quantity register
(see

3-36

ODT COMMAND SEQUENCES AND FUNCTIONS

$Q, Table 3-1).
A wide range of operations is possible using this
command, as reflected in the following sequences:
_0,370;R
0,0=000370
-2,16*$00+6=003364
-0, 16=000406
-3 70+16=000406
-0,16+16+2=000426
-370+16+16+2=000426
l.6+370=000406
-16-370=177426
- -370+16=177426
--370-16=177372
--177777+16+16=000035
-+l+l 6+16==000035
-177777+16+16=000033
--1+16+16=:000033
-232323=03:2323
Note in the sequence above that any expression value that references
relocation register 0 causes ODT to take the current contents of that
register as an argument in evaluating the
expression.
Those
expressions beginning with 0 cause the value 370(8) to be used as the
effective value of that element, as established through the initial
command of the sequence above. Any of the relocation registers can be
used in this manner.

~·

Both positive and negative values may be specified as arguments in an
expression,
as reflected throughout the examples above.
ODT performs
the necessary arithmetic calculations and prints out the result as a
6-digit octal value.
Note also that any expression value preceding the equal sign is
truncated to 16 bits before being evaluated and printed in 6-digit
octal form, as shown in the last expression in the above sequence.

3. 16

USING SPECIAJL ARGUMENTS IN ODT COMMANDS

The special arguments described below may be
elements a and k in ODT commands.

3.16.l

used

place

the

Current Location Indicator:

When used in a command sequence, the dot (.) represents the address of
the currently-open location, as shown below:

_1000/000000 .=001000

3.16.2

;DOT (.) REFERENCES ADDRESS OF
;LAST OPENED LOCATION.

Constant Register Indicator:

The user may store any 16-bit expression value
in the constant
register
(see $C, Table 3-1).
To open the register and print its
contents, the user issues the $C/ command.
Any new value desired can

3-37

ODT COMMAND SEQUENCES AND FUNCTIONS
then be entered directly, followed by a <CR> command. The value so
contained in the constant register may then be used in any subsequent
ODT operations by typing the letter C as an argument in a command.
The example below shows how the
modified:
_.$C/000000 123 <CR>
_/000123

3.16.3

constant

accessed

and

;CONSTANT REGISTER OPENED, MODIFIED
;TO CONTAIN 123, FOLLOWED BY RETURN
;COMMAND.
;CONSTANT REGISTER OPENED, CURRENT
;CONTENTS ARE PRINTED.

Quantity Register Indicator:

Each time ODT prints a value on the console, the value
is stored in
the quantity register
(see $Q, Table 3-1) • The value so stored may
then be used in any subsequent ODT operations by typing Q as an
element of a command.
This facility is useful in modifying open
locations.
For example, if location 1342 contains a value which is
too small for current debugging purposes, the value may be modified,
as shown in the first line of the command sequence below:
_1342/173214 Q+lO <CR>
_/17 3224

As a second example, assume that the contents of user general register
3 point to a routine that has been relocated through relocation
register 5. The following command sequence might then occur:

_5,20=013644

;ADD THE VALUE 10 TO THE CURRENT
:CONTENTS OF LOCATION 1342.
:SLASH OPENS PREVIOUS LOCATION,
;PRINTS ITS CONTENTS, AND STORES NEW
;VALUE IN Q REGISTER.

Therefore, when Q is employed as an argument in an expression in this
manner,
the contents of the currently-open location are modified to
contain the octal equivalent of the expression. Note in the last line
of the sequence above that issuing the slash command verifies the
modification of the previously-open location.

_$3/013624 Q;5R

~
~·· ·

;SETS RELOCATION REGISTER 5 TO 013624
; (THE CURRENT VALUE OF Q REGISTER) •
:EVALUATES THE RELOCATABLE ADDRESS
:EXPRESSION, PRINTS THE VALUE OF THE
;EXPRESSION, AND STORES THIS WORD IN
;THE QUANTITY REGISTER.

After the relocatable address expression in the example above is
evaluated,
the quantity register contains the value 013644(8), while
relocation register 5 retains the value 013624(8) set in the preceding
command.

3-38

ODT COMMAND SEQUENCES AND FUNCTIONS
3.16.4

Radix-SO Operator:

The asterisk (*) is an arithmetic operator that is used primarily in
the calculation of Radix-50 arguments.
Calculating such arguments is
necessary if the user wants to enter any of the Radix-50 characters
into a word location. The asterisk (*) allows the user to derive the
6-digit octal equivalent of the desired Radix-50 character(s) so that
the proper value can be entered 'into the appropriate location. Table
3-2 lists ·all the legal Radix-50 characters,
together with an
equivalent numeric value that is used in conjunction with the asterisk
to calculate a 6-digit octal representation of any combination of up
to three Radix-50 characters.
By consulting Table 3-2, the user can calculate any desired 1- to
3-character Radix-50 sequence for entry into a word location.
For
example, if it is desirable to enter the Radix-50 characters ABC into
a given location, the 6-digit octal representation of these characters
is calculated as follows:
_1*2*3=003223
Note from this sequence that the numeric values 1, 2, and 3 are taken
from Table 3-2 as the arguments to be used in the calculation. For
this purpose, these numeric values represent the Radix-50 characters
A, B,
and C.
Hence, the 6-digit result of this calculation is the
octal value that must be entered into the desired location to
correctly represent the intended Radix-50 sequence.
Table 3-2 may be used in this manner to calculate any corresponding
6-digit octal value of any desired combination of three Radix-50
characters, including the special characters space, $, and dot (.).
The following sequences illustrate how the Radix-50 operator
be used:

(*)

may

_1052/174777 %999 1*2*3=003223 3223 <CR>
_%ABC
_10S4/003151 %AAA 1*3*5=003275 327S <CR>
%ACE
In the examples above, note that the contents of the open location are
first interpreted by typing the percent sign (%). This command,
although entirely optional, permits the user to ascertain the current
contents of the location in Radix-50 form (see section 3.14.4). At
this point, if the user elects to enter some other Radix-50 character
sequence, he may do so by calculating its value as shown above and
then entering this value before closing the location.
Also optional
is the second line of each sequence which interprets the new Radix-SO
character(s) in the changed location to verify their accuracy.
As a further example,
the user may wish to enter the Radix-SO
characters $TJ into location 1054. After opening this location, Table
3-2 is consulted for the corresponding numeric values to be used in
the calculation.
These values are determined to be 33, 24, and 12.
The sequence of ODT operations then proceeds as follows:
1US4/1241S7 33*24*12=125752 1257S2 <CR>
=%$TJ

3-39

ODT COMMAND SEQUENCES AND FUNCTIONS
Note that spaces (blanks) are valid characters in deriving .Radix-5 0
character sequences. A space is represented in the calculation as 0 ,
as shown below:
_1*0=000050
0*1=000001
-2*0*3=006203
Table 3-2
Legal Radix-50 Characters and Numeric Equivalents
Radix-50
Character

Numeric
Equivalent

Radix-50
Character

Space
A

0
1
2
3
4
5
6
7
10

D
E
F
G
H
I

J
K

L
M
N

0
p
Q

s
3.17

u
v

w
x
y

z
$

Unused
0
1
2
3
4

12
13
14
15
16
17
20
21
22
23

REENTRY VECTOR REGISTER:

5
6
7
8
9

Numeric
Equivalent
24
25
26
27
30
31
32
33
34
35
36
37
40
41
42
43
44
45
46
47

When a task is requested frequently for execution,
as
is often the
case in debugging operations, it may be desirable to fix an installed
task in memory.
Once fixed in memory, the task does not relinquish
its memory space, and a fresh copy of the task is not loaded from disk
each time the task is requested for execution.
If the user is performing multiple executions of the task during a
debugging session, the reentry vector register is useful in connection
with such a fixed task.
This register may be set to a value which
causes the task to be reentered directly at its own starting address,
rather than at ODT's starting address.
Initially, when ODT is linked to the user task,
the reentry vector
register has a value of minus one (-1). The first time the task is
executed, this register is incremented to zero (0).
The next time the
task is requested for
execution, ODT inhibits the printout of the
task's name following the "ODT:" console output.
The absence of the
task name
in this console response indicates that the task is still
fixed in memory. At this point, the user may set the reentry vector

3-40

IODT COMMAND SEQUENCES AND FUNCTIONS
register to ~ value of one (l), or any positive nonzero value, causing
the task to be reentered at the address contained in $7
(the program
counter) when the G command is again issued to begin task execution.
The significance of this option is that any task locations modified
(patched)
during the initial debugging pass are retained. Thus, the
task, as initially executed, remains in core, and the user need not
start all over again each time the task is executed.
When this option .is exercised, task execution is initiated without
reentering ODT.
In employing this option, however, the user must be
aware of any execution-dependent variables in the task. Switch values
or counters, for example, may be altered during the course of initial
task execution and may not be valid for a subsequent execution.
Such
possibilities must be kept in mind when performing multiple executions
of a fixed task.

3-41

CHAPTER 4

OPERATING PROCEDURES

ODT is supplied to the user as a relocatable object module which must
be linked by the Task Builder to the user program. The output of the
Task Builder is thus an executable task image comprising both the user
object modules and ODT.
After loading, this task image file is the
focus of all ODT debugging operations.
The term Task Builder, as used in this manual refers to the particular
Task Builder of the system being used, i.e., that of RSX-llM, RSX-llD,
or IAS.
The user
is referred to the appropriate Task Builder
Reference Manual for a more detailed discussion of its functions.

4 .1

FILE TYPE OR lE!XTENSION VALUES

Any number of input files can be specified for the Task Builder.
If
the
input file sp,~cification does not contain an explicit declaration
of the file type (RSX) or extension (IAS), the Task Builder assumes
the default value .OBJ for the input file.
The Task Builder produces three types of output files:

4.2

TSK

Executable Task Image File

MAP

Memory Allocation Map File

STB

Task Image Symbol Table File

OUTPUT FILE SWITCH OR QUALIFIER OPTIONS

The output file switch (RSX)
or qualifier
(IAS)
options that are
applicable to the ODT user, relate to the executable task image file
(TSK). The options of specific interest are:
/DA
(RSX)
or
/DEBUG
(IAS)

This option indicates that a debugging aid (ODT) is to be
linked with the user task,
causing the object module
ODT.OBJ, which resides in the system area (SY: [1,1]}, to
be linked automatically into the task image.

When the /DA switch under RSX, or the /DEBUG qualifier of the LINK
command
under
IAS is specified,
registers 0 through 4 become
initialized with the following values.
Register 0 contains the task's
entry-point address.
User registers 1 and 2 contain the run-time name

4-1

OPERATING PROCEDURES
of the task in Radix-50 form;
register 1 contains the first
three
characters of the task name, and register 2 contains the last three
characters.
Registers 3 and 4 contain the version number of the
user's task if an .!DENT assembler directive is present in the task,
or the version number of ODT if no .IDENT directive is present.
When
ODT gains control at task initiation, user general registers 0 through
7 are saved in ODT's registers $0 through $7, and ODT's stack
is set
up. While ODT is in control, the ODT stack is used, and ODT registers
$0 through $7 contain the current values of the corresponding user
program registers. When ODT returns control to the user program, the
task's starting address is restored to the program counter,
and the
task's stack and other general registers are likewise restored.
control
is
For tasks that were built without a debugging aid,
transferred directly to the user program's entry-point (transfer)
address upon task initiation.

4 .• 3

4~3.1

LINKING AND INITIATING ODT

RSX-11 Systems

As an example of linking and initiating ODT with the user program,
assume that an object module named TEST.OBJ is to be linked with ODT.
The following sequence of keyboard commands and responses would then
occur:
>TKB
TKB>TEST/DA=TEST
TKB>/
TKB>ENTER OPTIONS:
TKB>TASK=TEST
TKB>/
>INSTALL TEST
>RUN TEST
ODT:TEST

The first line of the command sequence above requests the execution of
the Task Builder. The second line contains the Task Builder prompting
sequence TKB>, indicating its readiness to accept input;
the entry of
the
input/output file
specifications then follows on the same line.
This command string indicates that ODT is to be linked with the user
program TEST.OBJ
in forming the executable task image output file
TEST.TSK.
In the third line, the user types a slash (/) in response to the Task
Builder prompting sequence to indicate that additional input is to be
entered. The Task Builder then responds with the fourth line,

4-2

OPERATING PROCEDURES
continuing with the TKB> prompting sequence in the fifth line to
indicate its readiness to accept additional
input;
the user then
establishes the task name with the entry TASK=TEST to complete the
line. The slash (/) entered in line six in response to the Task
Builder prompting sequence terminates this part of the input.
The seventh line of the sequence installs the task in the system, and
makes it available for execution. This process consists of building
an entry for the task in the system task directory, setting up various
pointers, and assigning devices to logical unit numbers. Line eight
requests the execution of the task, causing the system to respond with
the message ODT:TEST,
indicating that ODT has been given control.
Finally, the prompting character (_) on the last line indicates ODT's
readiness to accept user input to initiate the debugging session.

4.3.2

"""'

IAS System

The following example shows the linking of ODT with a user object
module
(TEST.OBJ)
under IAS,
and the initiation of the task image
(TEST.TSK).
PDS> LINK/DEBUG TEST
PDS> RUN TEST
ODT:TEST

4.4

;LINK ODT WITH TEST.OBJ
;EXECUTE TEST.TSK

OTHER DEBUGGING AIDS

Other debugging aids can be specified by the user in place of
follows:

ODT

RSX:
TKB>TEST==ERRTST/DA, TEST

; /DA ON INPUT, NAMES USER DEBUG AID

IAS:
PDS> LINK/DEBUG:ERRTST TEST

;ERRTST IS USER DEBUGGING AID

These forms of /DA and /DEBUG have the following effects:
1.

The transfer address in the alternate debugging aid overrides
the task transfer address.

On initial task load,
indicated values:

the

following

registers

have

the

RO - Transfer address of task
Rl - Task name specified at task-build time in Radix-50
format (word #1)
R2 - Task name (word #2)
R3 - Version number of user's task (if .!DENT assembler
&
directive is present in the task)
R4
or
Version number of the first input file encountered
that contains an .IDENT directive
If the run-time task name is desired,
rather
than the
task-build task name,
the user can issue the GET TASK
PARAMETERS Executive directive, which returns the run-time
name.

4-3

OPERATING PROCEDURES
4e5

RETURNING CONTROL TO THE BOST SYSTEM

If ODT is awaiting keyboard input, typing an X causes execution of the
system Task Exit directive, thereby terminating task execution and
returning control to the host operating system.

4-4

CHAPTER 5
ERROR DETECTION

5.1

COMMAND INPUT ERRORS

ODT checks the legality of an address when commanded to open a
location for examination or modification.
If an error is detected,
ODT responds by printing the question mark (?) character, followed by
the underline (_) prompting character on the next line. For example,
if the command
177774/ ?
references nonexistent memory or an address outside the task's
partition, the request is ignored, and the appropriate typeouts occur.
In addition, a command such as
$20/ ?
which specifies an invalid (nonexistent) register, causes ODT to flag
the line with a question mark (?), ignore the request, and print the
prompting character.
In general, typing an illegal character or command causes
ignore the input, print the question mark error indicator

ODT

and wait for a valid command.
To cause ODT to ignore a command just entered, any illegal character
(such as the decimal value 8 or 9) may be typed, causing the command
to be treated as an error (ignored).
ODT suspends task execution whenever a breakpoint location
is
encountered
(i.e.,
the user program traps to ODT's breakpoint
processing routine).
If the breakpoint routine
is entered and no
known breakpoint has caused the trap action, ODT prints a message in
the form
BE:001542
and waits for another command.
In the example above,
the message
BE:001542 denotes a bad entry from location 001542 (see BE, Table
5-1). This type of error message may be caused by an illegal BPT
instruction in the user task,
setting the T-bit in the Processor
Status word ($8), or a branch to a location within ODT.
5-1

ERROR DETECTION

Although octal op code 000003
(the BPT instruction)
is a valid
instruction in a user program,
its use is discouraged, since this
instruction will result in an unwanted breakpoint when the program is
run under ODT control.

5.2

TASK IMAGE ERROR CODES

In addition to command input errors, ODT alerts the user to certain
hardware-detected errors that occur during task execution. Such
errors, which are attributable to problems in the task itself,
result
in a trap to one of the error-handling routines pointed to by the SST
vector registers in ODT (see $nV, Table 3-1). These registers, each
containing an entry-point address to an associated error-hand1ing
routine,
constitute the mechanism
through
which
ODT
handles
synchronous system traps.
Depending on the particular type of error
condition detected, ODT activates the appropriate error-handling
routine, which then evaluates the condition and prints out an error
code in the form
cc:k
where cc represents one of the 2-character alphabetic error codes
listed in Table 5-1,
and k represents the 6-digit octal address
following the location in error, unless the code is BE.
If the code
is BE,
k represents the address of the location in error. The
alphabetic error code and the address value are always separated by a
colon (:) •
At this point, the user can examine the error location,
register
values,
and other key locations in the task image.
If the cause of
the error can be determined, appropriate modifications can then be
made in the user task and noted on the assembly listing;
if the error
cannot be isolated, it is advisable to load a fresh copy of the entire
task and initiate a new debugging session.
Table 5-1
ODT Error Codes
Code

Meaning

MP*

Memory protect violation or illegal memory reference.

Odd address reference on word instruction.
(Also, on
some PDP-11 processors (e.g., PDP-11/45), the execution
of an illegal instruction is reported by this code
rather than by an IL.)

IOT instruction executed.

Reserved or illegal instruction executed.

Non-IAS/RSX-11 EMT instruction executed.

TRAP instruction executed.

T-bit exception.

T-bit was set, but

* Occurs only in RSX-llM systems
hardware (i.e., a mapped system).
5-2

equipped

with

setting
memory

was

not

management

ERROR DETECTION

Table 5-1 (Cont.)
ODT Error Codes
Meaning

Code

caused by a breakpoint, single-step mode, a Proceed
command, or a BPT instruction.
Probably caused by
improperly maintained task stack resulting in a word
(that happens to have its bit 4 set) being used as the
Processor Status Word (PS).
FP

Floating-point instruction error.

Breakpoint instruction executed at unexpected location.

5-3

CHAPTER .6
TRACE DEBUGGING AID

6.1

INTRODUCTION

The Trace program is a debugging aid for use in the development and
checkout of user-written tasks.
Trace produces a listing that
contains the register contents at the time each instruction in the
user task is executed. Execution of an entire task can be traced, or
up to four user-specified areas can be traced.
Selective tracing
allows the user to suppress the tracing of fully debugged subroutines
and system routines to achieve output faster.
As a debugging aid, Trace complements the capabilities of ODT.
Trace
is not an interactive program. It is specified for a task during task
building and is best suited for the debugging of relatively simple
tasks. Trace is effective when a quickly-obtained listing showing the
program's progress can be used to determine the cause of an error.
Two lines of register contents are printed on pseudo-device CL for
each instruction executed in the user's task. The first line contains
the contents of the following registers:

'-''

Current relative PC

Current PC

Next PC

Directive Status word

The relative PC is computed by subtracting a user-specified bias from
the actual PC.
In this way,
the trace output can be more easily
compared with a module listing.
The second line contains the following register contents:
1.

Contents of RO through RS and SP,

Contents of the top of the stack.

See Figure 6-1 for an example of Trace output.
Trace is included as an OBJ file named TRACE.OBJ under
the system disk.

6-1

UFD

[1,1]

TRACE DEBUGGING AID

000366 000566 000572 174020 000001
000566 131574 051025 140750 000000

000000

000176

000444

000372 000572 000574 174020 000007
000566 131574 051025 140750 000000

000000

000200

000000

000374 000574 000576 174020 000007
000566 131574 051025 140750 000000

000000

000200

000000

000376 000576 001626 174020 000007
000566 131574 051025 140750 000000

000000

000176

000602

000000

000200

000000

000402 000602 000604 :1.74020 000007
000566 13:1.574 051025 :1.40750 000000

000000

000200

000000

000404 000604 001220 :1.74020 000007
000566 131574 051025 140750 000000

000000

000176

000610

0 0 :I. 4 2 6

0 0 :I. 6 ::? 6

000566

0 0 0 ,1) 0 2

131574

:I. 7 4 0 2 0

051025

Figure 6-1

6.2

000007

140750

'"";

Sample Trace Output

OPERATIONAL INFORMATION

The Trace module must be built into the task. Task Builder operation
is described
in the IAS, RSX-llD, and RSX-llM Task Builder Reference
Manuals.
Procedures specific to Trace are described below.
1.

Assemble the program in the normal fashion.

Include the request for Trace in the command string to the
Task Builder when building the task. Trace is requested as
described in section 4.4, but here, specifying its disk area:
IAS:
PDS> LINK/DEBUG: [l,l]TRACE PROGl
RSX:
TKB>PROGl.TSK=PROGl.OBJ, [l,l]TRACE/DA

If desired, use the GBLPAT Task Builder option to specify the
relative PC bias and one or more ranges to be traced. The
GBLPAT option has the following formats for specifying a bias
and ranges, respectively.
GBLPAT=segname:.BIAS:bias value
GBLPAT=segname:.RANGE:range/low:range/high: •..
:range4high

segname

= name of the task's root segment.

6-2

:range4low

TRACE DEBUGGING AID

bias value

octal value to be subtracted from the actual PC to
compute the relative PC.
If a bias is not
specified, the initial stack pointer is used.

range/low,
range4low,

the low address, relative to the bias value, of
is
any of up to four
ranges.
The address
expressed as an octal value.

range/high,
range4high,

the high address, relative to the bias value, of
is
any of up to four
ranges.
The address
expressed as an octal value.
NOTE
Both the low and high addresses of a range must be
specified.

Example 1:

The following GBLPAT options are used to restrict
the tracing of PROGl to a single module located at
address 1364 (octal).
GBLPAT=PROG1:.BIAS:l364
GBLPAT=PROG1:.RANGE:0:214
The low and high range limits specified above
relative to the specified bias value.

Example 2:

are

and
Task PROG2 consists of a single module
(PROG2)
The
system
subroutines
linked above PROG2.
following GBLPAT excludes these subroutines from
the trace.
GBLPAT=PROG2:0:1342
In this example, trace ranges are set relative to
the default bias (initial SP). The high limit is
the length of the module PROG2.

When task building is completed, run the task.
is printed on CL.

6-3

Trace

output

~'I

APPENDIX A
PROCESSOR STATUS WORD

The Processor Status Word (PS), stored at hardware location 777776,
contains information on the current status of the processor. The
information contained in this location includes the current and
previous operational modes of the processor (mapped system only) , the
current processor priority, an indicator which, when set, causes a
trap upon completion of the current instruction, and condition codes
describing the results of the last instruction executed.
The format
of the Processor Status Word is shown in Figure A-1 below.

I --

A.l

PRIORITY
CARRY
OVERFLOW
ZERO
NEGATIVE
TRACE TRAP
GEN REG SET
PREVIOUS MODE
CURRENT MODE

Figure A-1

Format of Processor Status Word

MODES (MEMORY MANAGEMENT OPTION)

Bits 15 and 14 of the Processor Status Word
indicate the current
processor mode, i..e., either User mode (11) or kernel mode (00). Bits
13 and 12 indicate the previous mode, i.e, the mode the machine was in
(User or Kernel) prior to the last interrupt or trap.
User and Kernel modes afford a fully-protected environment for
a
multiprogramming system by providing the system with two distinct sets
of processor stacks and memory segmentation registers for memory
mapping.
In user mode, a program is inhibited from executing a "HALT"
instruction, and the processor will trap through location 4
(location
10 on PDP-11/40)
if an attempt is made to execute this instruction.
Furthermore, the processor will ignore the RESET instruction (and the
SPL instruction on the PDP-11/45).
In Kernel mode, the processor will
execute all instructions.
A program operating in Kernel mode can map a user's program anywhere
in memory and thus explicitly protect key areas (including the device

A-1

PROCESSOR STATUS WORD

registers and the Processor
environment.

A.2

Status

Word)

from

the

user

operating

PROCESSOR PRIORITY

The current priority of the central processor is maintained in bits 7
through 5 of the Processor Status Word.
The central processor
operates at any one of eight levels of priority (0 through 7).
When
the central processor is operating at level 7 (the highest priority),
an external device cannot interrupt it with a request for service.
The central processor must be operating at a lower priority than the
external device's request in order for the interrupt to take effect.
The eight processor levels provide an effective interrupt mask. On
the PDP-11/45, these bits can be altered dynamically through the use
of the SPL (Set Priority Level) instruction. This instruction is
legal only in Kernel mode.

A.3

TRAP (T-BIT)

The trap bit (bit 4) can be set or cleared under program control.
When set, a processor trap will occur through location 14 upon
completion of the current user instruction, and a new Processor Status
word will be loaded.
The trap (T) bit is especially useful in
debugging programs, since it provides an efficient means for stepping
through the task one instruction at a time. ODT uses the T-bit to
execute instructions in the single-instruction mode (see section 3.7).

A.4

CONDITION CODES

The condition codes N, Z, V, and C (bits 3 through O,
contain
information indicating the result of the
processor operation. These bits are set as follows:
N=l,
Z=l,
V=l,
C=l,

A.5

respectively)
last central

if the result was negative.
if the result was zero.
if the operation resulted in an arithmetic overflow.
if the operation resulted in a carry from the
significant bit.

most

TRAP PROCESSING

Both interrupts and trap instructions automatically cause the previous
Processor Status Word and program counter to be saved on the stack and
replaced by the new values stored in the associated interrupt vectors.
The interrupt vectors contain a new program counter value and new
Processor Status Word. The user can cause the central processor to
switch modes automatically (context switching), or disable the trap
bit whenever a trap or interrupt occurs.

A-2

APPENDIX B
SEARCH ALGORITHMS

As described in section 3.8, ODT allows the user to search for
specific bit patterns in the task or to identify words in the task
which reference a specific location. The algorithms for these two
types of search operations are described below.

B.l

WORD/BYTE SEARCHES (W or N)

The word search compares selected bits in a range of memory words with
a user-specified search argument.
The bits to be compared in the
memory words and the search argument are defined through the search
mask register
{see section 3.8.1). If all the selected bits in any
given memory word and the search argument are equal, a match has
occurred, and ODT prints the "unmasked" task word.
The algorithm for the word search operation follows:

B.2

Fetch the memory word at the current address.

Perform the logical operation XOR {exclusive
memory word and the specified search argument.

Perform the logical operation AND on the result from
and the specified mask.

If a W search is being performed and the result of Step 3 is
zero, or if an N search is being performed and the result of
Step 3 is nonzero, print the address of the unmasked word and
its contents.

Add two (2) to the current address, fetch the word in the
next location, and go to Step 2.
If, after adding 2 to the
current address, the resulting value is greater than that
contained in the high search limit register {see $H, Table
3-1), print the underline (_) prompting character and return
control to the ODT command decoder routine to await the next
user command.

OR)

the

Step

EFFECTIVE ADDRESS SEARCH (E)

In the effective address search, ODT treats every task word within the
specified search range as a value which has a possible direct
relationship to the search argument, i.e., as a word which addresses a

B-1

SEARCH ALGORITHMS

specified location.
Each address to be compared is first masked by
the contents of the search mask register (see $M, Table 3-1) before
comparison.
Therefore, the contents of the mask register should
normally be set to 177777 for the E command.
In the algorithm for the effective address search described below, the
following symbology is used:
(X)

The contents of location X.

The effective address search argument.

Fetch the word at location X (the current location).

If (X) = K, i.e., if location X contains a value which is an
absolute address reference to the search agrument (i.e.,
contains the search argument itself), print the contents of
location X and go to Step 5.

If (X)+X+2 = K, i.e., if the contents of location X, as
indexed by the contents of the program counter (PC), are
equal to the search argument, print the contents of location
X and go to Step 5.

If low-order (X)x2+X+2 = K, i.e., if the contents of the
low-order byte at location X reference a location whose
address value is the same as the search argument, print the
contents of location X, and go to Step 5.

Add 2 to the current address.
If the resulting value is
greater than that contained in the high search limit register
(see $H, Table 3-1), print the underline (_) prompting
character and return control to the ODT command decoder
routine to await the next user command;
otherwise, go to
Step 1.

B-2

~
--:::i

INDEX

@ command, 3-6
Absolute address, 2-4
Address,
absolute, 2-4
odd-numbered, 3-3, 3-14
user-task, 3-1
Address calculation, 3-8
Address expression, 1-5
Address limits, 2-8, 3-21
Address search commands,
effective, 3-23, B-1
Addresses,
printing task, 3-1
Addressing,
relative, 3-25
Addressing forms, 1-5
Algorithms,
search, B-1
Angle-bracket,
left, 3-8
right, 3-7
Argument,
search, 3-21
Arguments in ODT,
special, 3-37
Arithmetic operations, 3-36
Arithmetic operator, 2-2
Arithmetic overflow, A-2
ASCII,
byte mode, 3-31
word mode, 3-31
ASCII character, 2-6
print byte mode, 3-34
print word mode, 3-35
Asterisk, 3-39

Back-arrow command, 2-4, 3-6,
3-26
Backslash command, 3-4, 3-34
Base address, 1-4
BPT instruction, 1-3, 2-7, 3-13,
3-16
Bracket,
left-angle, 3-8
right-angle, 3-7
Branch displacement, 3-7, 3-25
Breakpoint, 2-8
Breakpoint address register,
3-13 I 3-17
Breakpoint commands,
task, 3-15
Breakpoint instruction,
register, 3-13
Breakpoint proceed count,
register, 2-5, 3-14

Breakpoint trap, 1-4
Breakpoints, 1-3, 2-7
Byte mode, 3-2
Byte mode ASCII character,
print, 3-31, 3-34
Byte mode octal, 3-31

Carriage return, 3-2
Carry, A-2
Character,
double-quote, 3-35
print byte mode ASCII, 3-31,
3-34
print word mode ASCII,
3-35
prompting, 3-1
radix-50, 3-36
single-quote, 3-34
Circumflex, 3-5
Close current location, 3-2
Codes,
condition, A-2
task image error, 5-2
Command decoder routines, 1-1
Command input errors, 5-1
Command sequences and functions,
ODT I 3-1
Command string format, 4-1
Command string subset, 4-3
Commands,
effective address search,
3-23, B-1
fill, 3-24
go, 3-17, 3-41
listing, 3-29
offset calculation, 3-25
open, 3-2
proceed, 3-17
program execution, 3-17
relocation calculator, 3-29
relocation register, 3-27
single-instruction mode,
3-19
task breakpoint, 3-15
word/byte search, 3-21, 3-23
Condition codes, A-2
Console listing device, 3-13,
3-29
Constant register, 1-6, 2-5,
3-11, 3-37
Context switching, A-2
Count,
instruction, 3-20
proceed, 3-18
Index-1

INDEX {CONT . )

Instruction,
BPT, 1-3, 2-7, 3-13, 3-16
IOT; 3-15, 5-2
Instruction count, 3-20
Internal registers, 3-10
Interrupted sequence, 3-8
Interrupts, A-2
IOT instruction, 3-15, 5-2

Default values, 4-1
Device,
console listing, 3-13, 3-29
Devices,
terminal, 3-13
Directive Status Word register,
2-5, 3-11
Displacement,
branch, 3-7, 3-25
Double-quote character, 3-37

Kernel mode, A-1
Effective address search command,
3-23, B-1
Equal sign command, 3-36
Error codes, 3-14, 3-18, 5-2
Errors,
command input, 5-1
Execution commands,
go, 3-17, 3-41
proceed, 3-17
Expression, 2-1
address, 1-5, 2-1
examples of address, 2-1
Expressions,
forms of address, 1-5
Extensions, 4-1

File,
executable task image, 4-1
memory allocation map, 4-1
task image symbol table, 4-1
File switch options, 4-1
File types, 4-1
Fill command, 3-24
Format,
printout, 3-1
Format register, 3-1, 3-11
Forms,
addressing, 1-5

G (Go) command, 3-7, 3-41
General registers, 3-9

High memory limit register,
2-8, 2-9, 3-12, 3-21,
3-24

Input file switch options, 4-1
Input file type default value,
4-1

Left-angle bracket, 3-8
Levels of priority, A-1
Limit,
high and low memory, 2-8,
2-9, 3-12, 3-21, 3-24
Line feed, 3-2
Linking and initiating ODT, 4-2
Listing command, 3-29
Location,
close current, 3-2
closed, 2-1, 3-2
open byte, 3-4
open next sequential, 3-2
open PC relative, 3-6
open preceding, 3-5
open relative branch, 3-6
open word, 3-2
Location indicator,
current, 2-1, 3-37
Locations,
internal, 3-10
reprinting open, 3-33
Logical unit number, 3-29
Low memory limit register, 2-8,
2-9, 3-12, 3-21, 3-24
LUN register, 2-9, 3-13, 3-29

Mapped system, 1-4
Mask,
search, 2-8, 3-21, 3-22, 3-23
Memory allocation map file, 4-1
Memory management option modes,
A-1
Memory map, 1-4
Memory protect violation, 3-15
Mode,
byte, 3-2
kernel, A-1
user, A-1
word, 3-3
Mode ASCII,
byte, 3-31
word, 3-31
Index-2

INDEX (CONT. )

Mode ASCII character,
print byte, 3-34
print word, 3-35
Mode octal,
byte, 3-31
word, 3-31
Mode Radix-SO,
word, 3-31
Mode Radix-50 characters,
print word, 3-36
Modes,
memory management option, A-1
output, 3-33
output listing, 3-31

O command, 3-26
Octal,
byte mode, 3-31
word mode, 3-31
Octal byte value,
print, 3-34
Octal operator, 2-6
Octal register, 3-20
Odd address, 3-14, 3-35
Odd-numbered address, 3-3
Offset,
PC relative, 2-·7
relative branch, 2-4, 3-7
Offset calculation commands,
3-25
Offset value, 3-26
Open byte location, 3-4
Open location, 2-1, 3-2
Open next sequential location,
3-2
Open PC relative location, 3-6
Open preceding location, 3-5
Open relative branch offset
location, 3-7
Open word location, 3-2
Operating procedures, 4-1
Operational description, 1-2
output modes, 3-33
trace program, 6-2
Overflow,
arithmetic, A-2
Overlaid tasks, 3-16

P (Proceed) command, 3-17
PC, 2-4
PC relative location,
open, 3-6
PC relative offset, 2-7
PC relative reference, 3-6
Percent sign, 3-36, 3-39

Pointer,
stack, 3-10
Position-independent code, 3-28
Print byte mode ASCII character, 3-34
Print octal byte value, 3-34
Print word mode ASCII characters,
3-35
Print word mode Radix-SO
characters, 3-36
Print task addresses, 3-1
Printout format, 3-1
Priority,
levels of, A-1
processor, A-1
Priority level, 1-3
Privileges, 1-3
Procedures,
operating, 4-1
Proceed count, 3-19
Processing,
trap, A-2
Processor priority, A-1
Processor status register,
3-11
Processor status word, 2-7,
3-10, 3-20, A-1
Processor trap, A-2
Program counter, A-2
Program execution commands,
3-17
Program section, 1-4
Prompting character, 1-6, 3-1

Qualifiers, 4-1, 4-2
Quantity register, 2-5, 3-12,
3-36
Quantity register indicator,
3-38
Quantity register operator,
2-5
Quotes,
double, 3-37
single, 3-34

Radix-SO,
word mode, 3-31
Radix-50 characters,
print word mode, 3-36
Radix-50 operator, 2-2, 2-6,
3-39
Reentry vector register, 2-5,
3-12 I 3-40
Reference,
PC relative, 3-6
Index-3

INDEX (CONT. )

Register,
breakpoint address, 3-13, 3-17
breakpoint instruction, 3-13
breakpoint proceed count,
3-14
constant, 1-6, 2-5, 3-11
Directive Status Word, 2-5,
3-11

format, 2-5, 3-1, 3-11
high memory limit, 2-5, 3-12,
3-21, 3-24
low memory limit, 2-5, 3-12,
3-21, 3-24
LUN, 2-9, 3-13, 3-29, 3-30
processor status, 3-11
quantity, 2-5, 3-12, 3-36
reentry vector, 2-5, 3-12,
3-40
relocation, 1-6, 2-7, 3-1,
3-7, 3-12, 3-20, 3-37
search mask, 3-11, 3-21, B-1
SST stack contents, 3-15
Register commands,
relocation, 3-27
Register indicator,
constant, 3-37
quantity, 3-38
Register operator,
constant, 2-5
quantity, 2-5
relocation, 2-2
Registers,
accessing general, 3-9
accessing special ODT, 3-10
breakpoint address, 2-5
breakpoint instruction, 2-5
breakpoint proceed count, 2-5
general, 3-18
:internal, 2-2
LUN, 2-5
relocation, 1-4, 2-5
SST vector, 2-5, 3-14, 5-2
stack contents, 2-5
Relative addressing, 3-25
Relative branch offset, 2-4, 3-7
Relative reference,
:l?C I 3-6
Relocatable address, 3-29
Relocation bias, 1-4, 3-29
Relocation calculator,
commands, 3-29
Relocation register, 1-5, 2-7,
3-1, 3-7 I 3-12, 3-20 I 3-37
commands, 3-27
operator, 2-2
Relocation registers, 1-4, 2-5
Reprinting open locations, 3-33
Reserved, illegal,
instruction, 3-15

Return to interrupted sequence,
3-8
Right angle-bracket, 3-7
Routines,
breakpoint, 5-1
command decoder, 1-1
command execution, 1-1
utility, 1-2
RUBOUT, 2-6
Running the user task, 3-17

S command, 3-19
Search,
effective address, B-1
word, 3-21
Search algorithms, B-1
Search argument, 3-22, 3-23
Search argument register, 2-5,
2-7, 2-9, 2-10, 3-12, 3-21,
3-24
Search commands,
effective address, 3-23
word/byte, 3-23
Search limits, 3-21
Search mask, 2-8, 3-21, 3-22, 3-23
Search mask register, 3-11, 3-21,
B-1
Search operations, 3-21
Searches,
word/byte, B-1
Semicolon, 3-26, 3-27
Separator,
argument, 2-3
Sequence,
return to interrupted, 3-8
Sequences,
elements of keyboard, 1-4
Sequences and functions,
ODT command, 3-1
Single-instruction mode commands,
3-20
Single-quote character, 3-34
Slash, 4-3
Slash command, 3-3, 3-5, 3-9,
3-27, 3-31, 3-38
Special arguments, 3-37
SST stack contents register,
3-15
SST vector registers, 2-5, 3-14, 5-2
Stack, A-2
Stack contents registers, 2-5
Stack pointer, 3-10
Status word,
processor, A-1
Switch options,
input file, 4-2
output file, 4-1
Index-4

INDEX (CONT.)

Symbols,
ODT characters and, 2-1
System,
mapped, 1-4
unmapped, 1-4

T-bi t, 3-19
T-bit trap, 3-14
Task,
initiate or resume, 3-15
Task breakpoint commands, 3-15
Task breakpoints,
user, 1-3
Task Builder, 1-4, 4-1, 4-5
Task exit, 2-10, 4-4
Task image symbol table file,
4-1
Task image error codes, 5-2
Tasks,
overlaid, 3-16
Terminal devices, 3-13
Trace program, 6-1
Trap, 3-15
breakpoint, 1-4
processor, A-2
T-bit, 3-15
Trap (T-bit) , A-2
Trap processing, A-2
Type default values,
input file, 4-1
output file, 4-1
Types,
file, 4-1

Underline, 2-4, 3-6, 3-26
UNITS=, 3-13
Unmapped system, 1-5
Up-arrow command, 3-5
User mode, A-1
User task,
running the, 3-17
User task address, 3-1
User task breakpoints, 1-4
Utility routines, 1-2

V command, 2-10, 3-14

W command, 3-21
Word,
processor status, A-1
Word ASCII,
byte, 3-31
Word mode, 3-34
Word mode ASCII, 3-31
Word mode ASCII characters,
print, 3-35
Word mode octal, 3-Jl
Word mode Radix-50, 3-33, 3-36
Word search, 3-21
Word/byte searches, B-1
Word/byte search commands, 3-21,
3-23
X command, 2-10, 4-4

Index-5

IAS/RSX-11
ODT Reference
Manual
DEC-11-0IODA-B-D

READER'S COMMENTS
NOTE:

This form is for document comments only. DIGITAL will
use comments submitted on this form at the company's
discretion. Problems with software should be reported
on a Software Performance Report (SPR) form.
If you
require a written reply and are eligible to receive
one under SPR service, submit your comments on an SPR
form.

Did you find errors in this manual?

1~
1·5

If so, specify by page.

Did you find this manual understandable, usable, and well-organized?
Please make suggestions for improvement.

I.~

1-£
I g>

1..2

,-su
I Cl>

16
CD

Is there sufficient documentation on associated system programs
required for use of the software described in this manual? If not,
what material :Ls missing and where should it be placed?

Please indicate the type of user/reader that you most nearly represent.

Assembly language programmer
[] Higher-level language programmer
Occasional programmer (experienced)
User with little programming experience
0 Student programmer
0 Non-programmer interested in computer concepts and capabilities

0
0

Name

Date-------------

Organization
Street-----·-----------------------------------------CitY-----------·-----------State ___________ Zip Code ____________
or
Country

-1

Do Not Tear - Fold Here and Tape
No Postage
Necessary
if Mailed in the
United States

111111

BUSINESS REPLY MAIL
FIRST CLASS PERMIT N0.33 MAYNARD MASS.
POSTAGE WILL BE PAID BY ADDRESSEE

RT/C SOFTWARE PUBLICATIONS TW/A14
DIGITAL EQUIPMENT CORPORATION
1925 ANDOVER STREET
TEWKSBURY, MASSACHUSETTS

Do Not Tear - Fold Here

01876

-I

I
I
I