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Document:	RSX-11M-PLUS and Micro/RSX Debugging Reference Manual
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RSX-ll M-PLUS and M icro/RSX
Debugging
Reference Manual
Order No. AA-JS09A- TC

RSX-ll M-PLUS and Micro /RSX
Debugging Reference
Manual
Order No. AA-JS09A-TC

RSX-ll M-PLUS Version 4.0
Micro/RSX Version 4.0

Digital Equipment Corporation

Maynard, Massachusetts

First Printing, July 1985
Revised, September 1987
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 be used or copied
only 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 Equipment Corporation or its affiliated companies.
Copyright ©1985,1987 by Digital Equipment Corporation
All Rights Reserved.
Printed in U.S.A.
The postpaid READER'S COMMENTS form on the last page of this document requests the
user's critical evaluation to assist in preparing future documentation.
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American Mathematical Society,

Contents
Preface

vii

Summary of Technical Changes

Chapter 1 Introduction to ODT
1.1
1.2

1.3
1.4
1.5

Overview of ODT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1
Linking ODT with a User Program . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-2
1.2.1
Linking ODT from MCR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-2
1.2.2
Linking ODT from DCL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-3
1.2.3
Linking to Enable Instruction and Data Space Features . . . . . . . . . . . . . . . . . 1-3
1.2.3.1 Enabling Instruction and Data Space . . . . . . . . . . . . . . . . . . . . . . . . . 1-3
1.2.3.2 Linking ODTID.OBI Explicitly . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-4
1.2.3.3 Enabling Supervisor-Mode Library Debugging . . . . . . . . . . . . . . . . . . . 1-4
1.2.4
Assigning ODT LUNs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-4
Invoking ODT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-5
Returning Control to the Host System. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-5
Interrupting a Debugging Session. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-6
1.5.1
Resuming a Debugging Session . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-6

Chapter 2 ODT Characters and Symbols
2.1
2.2

2.3

Variables Used in Command Descriptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-1
Address Expression Formats . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-2
2.2.1
Absolute and Relative Addressing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-2
2.2.2
Forming Expressions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-3
Operator and Command Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-4

iii

Chapter 3
3.1

3.2
3.3
3.4
3.5
3.6

Setting and Removing Breakpoints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-1
3.1.1
Setting Breakpoints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-1
3.1.2
Removing Breakpoints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-2
Beginning Task Execution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-3
Continuing Task Execution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-3
Using the Breakpoint Proceed Count . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-4
Stepping Through the Program . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-4
Setting Breakpoints in Overlay Segments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-5

Chapter 4
4.1
4.2
4.3

4.4
4.5
4.6
4.7
4.8
4.9
4.10
4.11

5.2

Oisplaying and Altering the Contents of Locations
with OOT

Altering the Contents of a Location . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-1
Closing a Location . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-2
Opening Word and Byte Locations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-2
4.3.1
Opening Word and Byte Locations at a Specified Address . . . . . . . . . . . . . . . 4-2
4.3.2
Reopening the Location Last Opened . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-3
4.3.3
Moving Between Word and Byte Modes . . . . . . . . . . . . . . . . . . . . . . . . . . 4-3
Opening the Next Sequential Location . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-4
Opening the Preceding Location . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-4
Opening Absolute Locations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-4
Opening PC-Relative Locations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-5
Opening Relative Branch Offset Locations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-5
Returning from a Calculated Location . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-6
Opening the Directive Status Word . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-6
Using Different Output Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-6
4.11.1
ASCII Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-6
4.11.2 Radix-50 Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-7

Chapter 5
5.1

Controlling Program Execution with OOT

Using Registers in OOT

General Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-1
5.1.1
Examining and Setting General Registers . . . . . . . . . . . . . . . . . . . . . . . . . . 5-1
5.1.2
Contents of General Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-2
ODT Internal Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-2
5.2.1
Relocation Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-5
5.2.1.1 Setting Relocation Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-6
5.2.1.2 Clearing Relocation Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-6
5.2.2
The Reentry Vector Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-6

Chapter 6
6.1

6.2

6.3
6.4

Memory Operations in ODT

Registers Used in Memory Operations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-1
6.1.1
Search Limit Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-2
6.1.2
Search Mask Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-2
6.1.3
Search Argument Register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-2
6.1.4
Device Control LUN Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-2
Searching Memory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-2
6.2.1
Searching for a Word or Byte . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-3
6.2.2
Searching for Inequality of a Word or Byte . . . . . . . . . . . . . . . . . . . . . . . . 6-3
6.2.3
Searching for a Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-3
Filling Memory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-4
Listing Memory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-4
6.4.1
Command Format . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-4
6.4.2
Listing Format . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-5

Chapter 7 Performing Calculations in ODT
7.1
7.2
7.3

Calculating Relocatable Addresses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-1
Calculating Offsets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-2
Evaluating Expressions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-2
7.3.1
Equal Sign Operator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-2
7.3.2
Current Location Indicator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-3
7.3.3
Constant Register Indicator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-3
7.3.4
Quantity Register Indicator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-3
7.3.5
Radix-50 Evaluation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-4

Chapter 8 Additional Debugging Aids
8.1

8.2

Accessing Other Debugging Aids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-1
8.1.1
MCR Command Line . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-1
8.1.2
DCL Command Line . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-1
The Trace Debugging Program . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-2
8.2.1
The Trace Listing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-2
8.2.2
Bias Values and Ranges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . : ..... 8-3
8.2.2.1 Specifying a Bias Value . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-3
8.2.2.2 Specifying Ranges to be Traced . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-3

Appendix A
A.l
A.2

Error Detection

Input Errors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-I
Task Image Error Codes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-2

Appendix B Processor Status Word
Index
Examples
6-1
8-1

ODT Listing Format . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-5
Sample Trace Output . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-3

Figures
B-1

Format of the Processor Status Word . . . . . . . . . . . . . . . . . . . . . . . . . . . . . B-1

Tables
2-1
2-2
2-3
5-1
5-2
7-1

Variables Used in ODT Command Descriptions . . . . . . . . . . . . . . . . . . . . . . 2-1
Forms of Address Expressions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-4
ODT Operators and Commands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-4
ODT Single Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-3
ODT Register Sets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-4
Numeric Equivalents of Radix-50 Characters . . . . . . . . . . . . . . . . . . . . . . . . 7-4

Preface

Manual Objectives
This manual describes the On-Line Debugging Tool (ODT) used to debug user task images. It
provides reference information on all ODT commands, as well as information on how to use
the commands to debug task images.

Intended Audience
This manual is intended for all systems and applications programmers who develop task images
under the RSX-llM-PLUS or Micro/RSX operating systems. Readers should understand the
user interface of the operating system that they are using. RSX-llM-PLUS users should be
familiar with the contents of the RSX-IIM-PLUS Guide to Program Development before reading
this manual. Micro/RSX users should be familiar with the contents of the Micro/RSX Guide to
Advanced Programming before reading this manual.

Structure of This Document
Chapter 1 gives an overview of ODT. It explains how to link the debugger into a user task
image and how to begin and end a debugging session.
Chapter 2 explains the special symbols used in ODT and includes a reference table with an
alphabetical listing of ODT commands. New ODT users should read Chapters 3 to 7 for
explanations of the commands before studying the table of commands in detail. Experienced
ODT users can use Chapter 2 for quick reference.
Chapter 3 describes the command used to begin program execution, to stop execution at
breakpoints, and to continue execution after breakpoints. It also explains how to execute a
program with one or more instructions at a time.
Chapter 4 explains how to open and close task locations, how to change the contents of
locations, and how to display the contents of locations in different modes.

vii

Chapter 5 describes all of the registers used by ODT. It includes reference tables as well as
explanations of how registers are set and cleared. Experienced ODT users may want to consult
the tables in this chapter, as well as those in Chapter 2, for quick reference regarding specific
registers.
Chapter 6 describes ODT's memory search, fill, and list capabilities.
Chapter 7 describes how to use ODT to perform arithmetic calculations.
Chapter 8 explains how to link debuggers other than ODT into a user task image. It describes
the Trace program, a debugging aid that can be used in conjunction with ODT.
Appendix A describes how ODT responds to errors in user input or program logic. It lists all
ODT error message codes in alphabetical order.
Appendix B shows the format of the Processor Status Word (PSW) and summarizes the functions
of its bits.

Associated Documents
The RSX-llM-PLUS and Micro/RSX Guide to Writing an I/O Driver contains information about
debugging a user-written driver. The information directory of the host operating system describes
other manuals that will be of interest to ODT users.

Conventions Used in This Document
The following conventions are used in this manual:
Convention

Meaning
A symbol with a 1- to 3-character abbreviation, such as IDELI or @ill, indicates
that you press a key on the terminal.

CTRL/a

This phrase indicates that you press the key labeled CTRL while simultaneously
pressing another key, such as C or Y. In examples, this control key sequence is
shown as A because that is how the system displays it on your terminal.
A

red ink

User input appears in red ink in the examples throughout this book. System
responses appear in black ink.

viii

Summary of Technical Changes

The following changes are reflected in this version of the manual:
C!

Information specific to the RSX-I1M operating system has been deleted.

The information on the Executive Debugging Tool (XDT) is now contained in the
RSX-llM-PLUS and Micro/RSX XDr Reference Manual.

This manual also corrects technical errors in the text and examples of the previous version.
It represents a significant reorganization of material that is intended to make information
more accessible to readers.

Chapter 1
Introduction to ODT
This chapter gives an overview of the an-Line Debugging Tool (aDT). aDT is a utility for
debugging task images. You can use aDT to do the following:
•

Control program execution

•

Display the contents of locations or registers

•

Alter the contents of locations or registers

•

Search and fill memory

•

Perform calculations

aDT commands consist of one character; some commands take a numeric or alphabetic character
as an argument. All aDT commands, and the symbols that are used in them, are listed in
Chapter 2. Chapters 3 to 7 describe how to use commands.

This chapter describes how to link the debugger into a user task image, initiate a debugging
session, and end a debugging session.

1. 1 Overview of ODT
aDT is special code that you link into your task image to help you debug your program. When
you run a task into which aDT has been linked, the debugger receives control of the task
automatically upon task initiation. Through aDT, you can then execute your task, gradually,
by setting breakpoints (by using BPT instructions in your program) at selected locations or by
stepping through the program one instruction at a time. Chapter 3 describes aDT commands
for controlling program execution.

You can examine any location in your program-instruction or data, word or byte-by" opening"
the location with aDT. While the location is open, you can immediately change the contents.
You can move forward or backward to examine and modify other locations. Thus, you can test
any number of modifications without rebuilding your task. Chapter 4 describes aDT commands
for examining and altering locations and for moving from one location to another.

Introduction to ODT 1-1

OOT operates through the use of a number of registers, all of which you can set and reset.
Some of these registers are used to store information about your program while OOT has
control. Eight registers can be set to the locations of breakpoints. Eight can be set to
relocation biases-the absolute base addresses of relocated object modules. You can use other
registers to store values that you may want to use repeatedly during your debugging session.
Chapter 5 describes the OOT registers. You can use OOT to search for bit patterns in memory,
to fill blocks of memory with a value, or to list blocks of memory on an output device.
Chapter 6 describes these operations.
During a debugging session, you can perform a variety of calculations: determining offsets,
evaluating arithmetic expressions, and constructing Radix-50 words. Chapter 7 describes these
calculations.

1.2 Linking ODT with a User Program
OOT is provided on your system as an object module, LB:[l,l]OOT.OBJ. The version of OOT
supporting the instruction and data space features of RSX-llM-PLUS and MicrojRSX operating
systems is provided in the object module LB:[l,l]OOTID.OBJ. To use OOT, you must link the
appropriate object module with the object module or modules of your program. When the
resulting task image is run, OOT is invoked and initiated automatically.
If the task image is overlaid, OOT is linked into the root segment so that the debugger will

always be available.
The following sections describe how to link OOT into a task image in different environments.
Section 1.2.1 describes how to link OOT if your command line interpreter (CLI) is the Monitor
Console Routine (MCR). Section 1.2.2 describes how to link OOT if your CLI is the DIGITAL
Command Language (OCL). Section 1.2.3 describes how to enable the instruction and data
space and supervisor-mode features of OOT used under some RSX-llM-PLUS and MicrojRSX
systems. Section 1.2.4 describes how to change logical unit number (LUN) assignments specific
to OOT.
The information in subsequent sections on initiating and using OOT applies equally to
RSX-llM-PLUS and MicrojRSX environments.

1.2.1 Linking ODT from MeR
To link OOT with your program or programs when your CLI is MCR, first invoke the Task
Builder (TKB) by typing TKB in response to the MCR prompt. The Task Builder replies with its
own prompt, TKB> . In response to this prompt, enter a TKB command and specify the name
of the file or files to be linked. Include the JOA switch, which indicates that a debugger (in
this case OOT, the default) should be linked into the image. OOT requires that you consult an
up-to-date map of your task. To obtain a current map of the image file produced, include the
jCRj-SP switches. The following example shows the resulting command line:
TKB>MYTASK/DA,MYTASK/CR/-SP=MYFILE1,MYFILE2 ffi[U

Object modules MYFILE1.0BJ and MYFILE2.0BJ are linked with object module OOT.OBJ in
directory [l,1] on the library device. The resulting task image is named MYTASK.TSK.
For more information on using the TKB, consult the RSX-11M-PLUS and MicrojRSX Task
Builder Manual.

1-2 Introduction to ODT

1.2.2 Linking OOT from Del
To link OOT with your program or programs when your CLI is OCL, use the /OEBVG qualifier
with the LINK command. OOT requires that you consult an up-to-date map of your task. To
obtain a current map of the image file produced, include the /MAP qualifier. The following
example shows the resulting command line:
$ LINK/MAP/DEBUG/TASK:MYTASK MYFILE1 .MYFILE2 ~

Object modules MYFILE1.0BJ and MYFILE2.0BJ are linked with object module OOT.OBJ in
directory [1,1] on the library device. The resulting task image is named MYTASK.TSK.
For further information on using OCL, consult the RSX-llM-PLUS Command Language Manual
or the Micro/RSX User's Guide, as appropriate to your system.

1.2.3 Linking to Enable Instruction and Data Space Features
To use the separate instruction and data space capabilities found on some RSX-llM-PLVS and
Micro/RSX systems, you must link your program with the object module LB:[l,l]OOTID.OBJ
instead of OOT.OBJ. Section 1.2.3.1 describes the MCR and OCL command lines that link
this object module for tasks that have been built using separate instruction and data space.
Section 1.2.3.2 describes the command line that links this object module explicitly. You use this
command line if, for example, you want to use data space windows but did not build the task
using separate instruction and data space. Section 1.2.3.3 describes how to enable debugging
for supervisor-mode libraries.

1.2.3.1 Enabling Instruction and Data Space
Separate instruction and data space is a feature of RSX-llM-PLVS and Micro/RSX systems.
OOT has the following instruction and data space commands: 0, I, V, and Z. To enable these
commands, you must link LB:[1,l]OOTIO.OBJ with your program instead of with OOT.OBJ.
(See Table 2-3 for a description of these commands.)
If your CLI is MCR and your task was built using separate instruction and data space, you
enable these commands by adding the /ID switch, as well as the /OA switch, to the TKB
command line. The following example shows the resulting command line:
TKB>MYTASK/DA/ID.MYTASK/-SP=MYTASK

You can add other switches to the command line as desired. Consult the RSX-11M-PLUS and
Micro/RSX Task Builder Manual for information on TKB command lines.
If your CLI is OCL and your task was built using separate instruction and data space, you enable
these commands by using the /COOE:OATA_SPACE qualifier, as well as /OEBVG, with the
LINK command. The following example shows the resulting command line:
$ LINK/DEBUG/CODE :DATA_SPACE/MAP MYTASK ~

You can add other qualifiers to the LINK command. See the RSX-llM-PLUS Command Language
Manual or the Micro /RSX User's Guide for more information.

Introduction to ODT 1-3

1.2.3.2 Linking ODTID.OBJ Explicitly
If your task was not built using separate instruction and data space, but you want to use data
space windows, you must link OOTID.OBI explicitly, and specify the debugger object module
in the MCR or OCL command line. The following example shows the resulting MCR command
line:
TKB>

The following example shows the resulting OCL command line:
$

1.2.3.3 Enabling Supervisor-Mode Library Debugging
On RSX-llM-PLUS and MicrojRSX systems with separate instruction and data space, you can
use OOT to debug supervisor-mode libraries. There are two ways to enable the Z command,
which sets the curr.e nt mode of OOT to supervisor mode. If your task was built using separate
instruction and data space, link it as described in Section 1.2.3.1. If your task was not built using
separate instruction and data space, link it by specifying OOTID.OBI explicitly, as described in
Section 1.2.3.2.
To set breakpoints or write into the supervisor-mode libraries, you must install the library with
READ jWRITE access and use either the jRW switch or the :RW argument on the RESSUP or
SUPLIB options, respectively. You can alternatively build the task as privilege: O.

1.2.4 Assigning ODT LUNs
When you build a task, the TKB automatically assigns default values for registers $00 and
$10. These registers contain the LUNs of the user terminal (TI) and the console device (CL),
respectively. However, you may want to assign new values for the registers. For example, if
you are debugging an editor task, you need to assign TI to another terminal so the output from
the task is directed to that terminal and does not interrupt your debugging session. Or, if you
want to direct output to another printer, you can assign CL to that printer. To override these
values, you can link your task by using the TKB options ASG and GBLPAT, as described in the
RSX-11M-PLUS and MicrojRSX Task Builder Manual. The following example shows a series of
task-build command options that direct OOT to use TT4 instead of TI:
TKB>MYTASK/DA. MYTASK/ -SP=MYTASK
TKB> / illill

lBill

Enter Options:
TKB>ASG=TT4: 1 illill
TKB>GBLPAT=MYTASK : .ODTL1 : 1
TKB> / / illill

illill

OOT allocates two extra LUNs to direct output to the TI and CL devices. The LUNs are pointed
to by the global symbols .00TLl and .00TL2. The global symbol .00TLl is the address of
a word that contains the OOT LUN for input and output to TI. The global symbol .00TL2 is
the address of a word that contains the OOT LUN for output to CL. To redirect the output to
either of these devices, you need to specify these symbols as parameters to the GBLPAT option.
For more information on reserved global symbols, see the RSX-11M-PLUS and MicrojRSX Task
Builder Manual.

1-4 Introduction to ODT

You can specify any terminal device (or logical resolving to the same). Also, you can use any
available LUN.
Alternatively, you may find it more convenient to assign a new value for CL before beginning
your debugging session. Use the MCR command ASN or the DCL command ASSIGN in one
of the following formats:
MCR>ASN devicename=CL :

or
DCL>ASSIGN CL: devicename

For more information on these commands, see the appropriate CLI manual for your system.

1.3 Invoking ODT
Regardless of what operating system or CLI you use, enter the RUN command and specify the
name of the task image file . ODT is invoked automatically when you run a task image into
which ODT has been linked, as described in the previous sections.
ODT responds with a message that indicates it has been invoked and that identifies the task
image it controls. On the next line, ODT displays its prompt, an underscore (_), which indicates
it is ready to accept commands.
The following example shows how ODT is invoked when HIYA.TSK is run:
>RUN HIYA [Bill
ODT:TT15

In response to the ODT prompt, you can enter any ODT command. ODT commands are
immediate-action commands; that is, ODT responds to the commands as soon as they are
typed, without waiting for a line terminator. Therefore, commands cannot be corrected once
they have been typed. You can, however, erase an incorrectly typed command argument by
typing an illegal character or command (such as a nonoctal number like 8 or 9) or by pressing
CTRLjU or by pressing the DELETE key. In response, ODT discards your input line, displays a
question mark (?), and prompts for another command.
Error detection is described in greater detail in Appendix A.

1.4 Returning Control to the Host System
To return control from ODT to the host operating system, type X in response to the ODT
prompt. This command causes execution of the system Task Exit directive, which terminates
task execution.

Introduction to ODT 1-5

1.5 Interrupting a Debugging Session
When you run a task linked with ODT, you can return to the command line interpreter (CLI)
prompt at any time by pressing CTRLjC. Your task is still active. To stop execution of the task,
enter the ABORT command in response to the MCR or DCL prompt. You cannot resume the
aborted debugging session; you can only run your program again.

Note
If your terminal has the CTRLjC abort characteristic set and if you want to be
able to resume a debugging session after pressing CTRLjC, you need to turn
CTRLjC abort off. Otherwise, pressing CTRLjC will have the same effect as
entering the ABORT command.
You can interrupt task execution without aborting your task and then continue debugging. After
pressing CTRLjC, use the commands described in the following section.

1.5. 1 Resuming a Debugging Session
RSX-llM-PLUS and MicrojRSX operating systems allow you to interrupt and then resume
task execution from the point at which the program was interrupted. To use this feature, do
not enter the ABORT command. Instead, type the DEBUG command in response to the CLI
prompt. This command overrides the task's current status. Among other things, ODT unsets
any WAIT-FaR-EVENT, STOP, or SUSPEND state that had been set. The DEBUG command
also causes aT-bit (trace bit) exception, as described in Appendix A. ODT generates a TE error
message, showing the current value of the program counter as the location where the error
occurred. This message is followed by the ODT prompt (_).
The DEBUG command has the following format:
DEBUG [taskname]

The task name argument is the specification of the task to be interrupted, as used when the
task was originally invoked. If you do not specify a task name, the default is a task initiated
through the RUN command.
The following example shows how the DEBUG command is used:
>RUN HIYA

lliITl

ODT :TT15
~G

ICTRL/ci

>DEBUG lliITl
TE:004020

The DEBUG command is especially useful if your program is caught in a loop, or if you need
to stop execution before the next breakpoint.

1-6 Introduction to ODT

Chapter 2
ODT Characters and Symbols
This chapter describes all the On-Line Debugging Tool (ODT) operators and commands, and it
explains the meanings of aDT -specific symbols used in this manual. (Symbols and conventions
common to the documentation set are listed in the Preface.)

2. 1 Variables Used in Command Descriptions
The command descriptions in Chapters 2 to 7 and Table 2-3 use lowercase alphabetic variables
to represent numeric and alphabetic arguments specified in commands. These variables are
explained in Table 2-1.
Table 2-1:

Variables Used In ODT Command Descriptions

Variable

Meaning

An address expression representing the address of a task image location. The
various forms in which an address expression can be specified are explained in
Section 2.2.

An octal value up to six digits long with a maximum value of 1777778 , or
an expression representing such a value. An expression may include arithmetic
operators or indicators, as described in Section 2.2.2. If more than six digits are
specified, aDT truncates to the low-order 16 bits. If the octal value is preceded
by a minus sign, aDT takes the two's complement of the value.

An octal value six digits long, used to represent a search mask.

An octal integer between 0 and 7.

An alphabetic character. A list of legal alphabetic characters is given in Table 2-3
where the variable x is used.

ODT Characters and Symbols

2-1

2.2 Address Expression Formats
An address expression, represented throughout this manual by the lowercase letter a, is an
expression interpreted by OOT as a 16-bit (6-digit octal) value. You use an address expression
to refer to a location in your task.
You can specify an address expression in either absolute or relative (relocatable) form, as
described in Section 2.2.1. You can include in the address expression various operators and
symbols, as described in Section 2.2.2.

2.2. 1 Absolute and Relative Addressing
Each location has an absolute address assigned to it when the task is built. You can refer to the
location by using this 6-digit octal value. However, when the task is built again, with modules
added or changed, this value may not refer to the same location. Therefore, it is often more
convenient to refer to locations by using relative (relocatable) addressing, which is less likely to
be affected by subsequent task builds.
When you use relative addressing, you refer to a location not by its absolute value but by its
position relative to a movable point. Usually, this movable point is the base (starting) address
of the module to which the location belongs, because the distance between the base address
and the addresses of locations within the module is easily determined from a task map or listing
and is not likely to change without your knowledge. The movable point can, however, be any
point that is convenient for debugging.
To use this form of addressing, you must first establish a simple means of referring to movable
points through the use of OOT's relocation registers $OR to $7R. Each time you run a task
built with OOT, consult a task map to determine the absolute addresses of convenient movable
points. The map's memory allocation synopsis contains the base addresses of all the modules
in the task. Follow the procedure described in Section 5.2.1.1 to set OOT's eight relocation
registers to absolute addresses.
Once a relocation register is set, you can use the number of that register, 0 to 7, in forming
relative addresses.
Relative Address Format

n,k
Parameters

n
The number of a relocation register, 0 to 7, representing $OR to $7R.
k

The relative location, that is, the distance of the desired location from the value contained in
register $nR. Usually, this is the location's position within the module whose base address
is the value of the register.

2-2 ODT Characters and Symbols

Thus, relative address 0,100 refers to location 100 within the module whose base address is
stored in ODT's relocation register $OR. Relative address 5,300 refers to location 300 within the
module whose base address is stored in relocation register $5R.
Bias value refers to the value stored in a relocation register. It is a quantity equal to the distance
(bias) between a relative location and its absolute address. Offset refers to the second part of a
relative address. It is the distance of a relative location from the closest value (less than that
location) stored in a relocation register. These terms are used throughout this manual.

2.2.2 Forming Expressions
An expression is a string of numbers, symbols, and operators that ODT interprets as a number.
For example, 3+6 is an expression; ODT would interpret it as the octal value II.
You can use an expression to represent an absolute address, a register containing a bias value,
or an offset, as described in Section 2.2.L
An expression used in an ODT session can contain any of the following elements:
•

Octal numbers. ODT will not accept input containing an 8 or 9. It treats these as illegal
characters and displays a question mark (?) and a new prompt.

•

The arithmetic operators a plus sign (+ ) or a space, indicating that values should be added,
or a minus sign ( -), indicating that the value that follows it should be subtracted from the
value that precedes it.

•

The unary operator minus sign, indicating that the value that follows it is negative and
should be interpreted in two's complement form.

•

ODT register indicators Q or C, representing $Q and $C registers, as described in
Sections 7.3.4 and 7.3.3, respectively. When Q or C is used to represent a register
containing a bias value, it must have a value in the range 0 to 7. When Q or C is used to
represent an offset, it may contain any 16-bit value.

•

The name of one of ODT's registers, used in the operations described in Chapters 5 and 6.

•

The current location indicator (.), as described in Section 7.3.2.

In evaluating expressions, ODT proceeds from left to right. It does not assign precedence to
any operator or recognize parentheses to establish precedence. Therefore, you must be careful
to form expressions so that they will be interpreted correctly. You can use the equal sign
operator (=), described in Section 7.3.1, to determine the value of expressions before using
them in ODT operations.
Table 2-2 shows how ODT interprets the various forms of address expressions. This table
assumes a value of 0034008 for relocation register 3 ($3R) and a value of 3 for the constant
register ($C).

ODT Characters and Symbols

2-3

Table 2-2:

Forms of Address Expressions

Address Expression Input

ODT Octal Interpretation

000005

-17

177761

3,150

003550

000003

C,lO

003410

C,C+C

003406

3,C

003403

Task general register 3

2.3 Operator and Command Summary
aDT commands are a combination of symbols and letters. Some commands have multiple

forms.
Table 2-3 summarizes the aDT commands and operators, which are explained in detail in
Chapters 3 to 7. The lowercase letters used in the command descriptions are explained in
Table 2-1.
Table 2-3:

OOT Operators and Commands

Format

Meaning

+ (plus sign) or space

Arithmetic operator used in expressions.
Add the preceding
argument to the following argument to form the current argument.

- (hyphen)

Arithmetic operator used in expressions. Subtract the following argument from the preceding argument to form the current argument.
Also used as a unary operator to indicate a negative value.

, (comma)

Argument separator. Separates the number of a relocation register
from a relative location to specify a relocatable address.

* (asterisk)

Radix-50 separator used in constructing Radix-50 words (see
Section 7.3.5).

. (period)

Current location indicator. Causes the address of the last explicitly
opened location to be used as the current address for aDT
operations.

; (semicolon)

Argument separator. Separates multiple arguments, which allows
an address expression or aDT register value to be identified.

[ill] (RETURN command)
or k [ill]

Command that closes the currently open location and prompts for
the next command. If RETURN is preceded by k, the value k replaces
the contents of the currently open location before it is closed.

2-4 ODT Characters and Symbols

Table 2-3 (Cont.):

OOT Operators and Commands

Format

Meaning

[0 (LINE FEED command)
or k [0

Command that closes the currently open location, opens the next
sequential location (a word or a byte, depending on the mode in
effect), and displays its contents. If LINE FEED is preceded by k, the
value k replaces the contents of the currently open location before
it is closed.

, or k'

Command that closes the currently open location, opens the
immediately preceding location, and displays its contents. If' is
preceded by k, the value k replaces the contents of the currently
open location before it is closed.
Command that interprets the contents of the currently open location
as a Program Counter (PC) relative offset and calculates the address
of the next location to be opened; then closes the currently open
location, and opens and displays the contents of the new location
thus evaluated. If _ is preceded by k, the value k replaces the
contents of the currently open location before it is closed.

@ork@

Command that interprets the contents of the currently open word
location as an absolute address, closes the currently open location,
and opens and displays 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>

Command that interprets the low-order byte of the currently open
word location as a relative branch offset, and calculates the address
of the next location to be opened, then closes the currently open
location, and opens and displays 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.

< or k <

Command that closes the currently open location (opened by a _,

@' or > command), and reopens the word location most recently
opened by a /' LINE FEED, or 'command. 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.
$n

Expression that represents the address of one of eight general
registers, where n is an octal digit identifying RO-R7.

ODT Characters and Symbols

2-5

Table 2-3 (Cont.):

OOT Operators and Commands

Format

Meaning

$x or $xn

Expression that represents the address of one of ODT's internal
registers, where x is one of the following alphabetic characters, and
n is one octal digit. Registers exist within ODT in the following
order:
S
Processor Status register (hardware PS)
W

Directive Status Word (DSW) 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

Synchronous System Trap (SST) vector registers

SST stack contents registers

Device control LUN (logical unit number) registers

" or a"

Word mode American Standard Code for Information Interchange
(ASCII) operator. Interprets and displays the contents of the
currently open (or the last previously opened) location as two ASCII
characters, and stores 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 displayed.

, or a'

Byte mode ASCII operator. Interprets and displays the contents of
the currently open (or the last previously opened) location as one
ASCII character, and stores this byte 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 displayed.

2-6 ODT Characters and Symbols

Table 2-3 (Cont.):

OOT Operators and Commands

Format

Meaning

% or a%

Word mode Radix-50 operator. Interprets and displays the contents
of the currently open (or the last opened) location as three Radix-50
characters, and stores 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 displayed.

/ or a/

Word mode octal operator. Displays the contents of the last word
location opened, and stores 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 displayed.

\ or a\

Byte mode octal operator. Displays the contents of the last byte
location opened, and stores this octal byte in the quantity register
($Q). If \ is preceded by a, aDT takes the value a as the address of
a byte location to be opened and displayed.

Command that interprets and displays expression value k as six
octal digits and stores this word in the quantity register ($Q).

8, 9,
IDELI,
or ICTRLjul

Illegal expressions that cancel the current command. aDT then
awaits a new command. The decimal values 8 and 9 are not legal
characters and, thus, when entered, cause aDT to ignore the current
command.

Command that removes all breakpoints from the user task.

Command that removes the nth breakpoint from the user task.

a;nB

Command that sets breakpoint n in the user task at address a. If n is
omitted, aDT assumes the lowest-numbered sequential breakpoint
available.

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

Command that accesses data space. After this command is issued,
aDT interprets all references to locations as referring to the data
space of the task.

E or kE
or m;E
or m;kE

Command that searches memory between the address limits specified by the low memory limit register ($L) and the high memory
limit register ($H). aDT examines 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 1777778 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 aDT initiates
the search. If E is preceded by m, the current contents of $M are
replaced with the value m before aDT initiates the search.

ODT Characters and Symbols 2-7

Table 2-3 (Cant.):

OOT Operators and Commands

Format

Meaning

For kF

Command that fills 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 ODT initiates the fill operation.

G or aG

Command that begins task execution by following these steps: sets
BPT instructions in or restores BPT instructions to all breakpoint
locations in the task image; restores the Processor Status Word
(PSW) and user program registers; and starts execution at the
address specified by the program counter (user register $7). If
G is preceded by a, the value a replaces the current contents of $7
before proceeding as described above.
Command that accesses instruction SDace. After this command is
issued, ODT interprets all references t~ locations as referring to the
instruction space of the task.

Command that, using the relocation register whose contents are
equal to or closest to (but less than) the address of the currently
open location, computes the physical distance (in bytes) between
the address of the currently open location and the value contained
in that relocation register. ODT displays this offset and stores the
value in the quantity register ($Q).

Command that computes 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. ODT displays this offset
and stores the value in the quantity register ($Q).

a;nK

Command that computes the physical distance (in bytes) between
address a and the value contained in relocation register n. ODT
displays this offset and stores the value in the quantity register ($Q).

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

Command that lists 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. 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 the value n
is either zero or not specified, the display goes to your terminal
(II). If a nonzero value is specified for n, the display goes to the
console (CO).

2-8 ODT Characters and Symbols

Table 2-3 (Cont.):

OOT Operators and Commands

Format

Meaning

N orkN
orm;N
or m;kN

Command that searches 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 that do not match
those of the search argument specified in the search argument register ($A). Only bit positions set to 1 in the mask are compared.
This search is identical in form and function to the word (W) search
described below, except that ODT performs a test for inequality.

aO or a;kO

Command that calculates and displays the PC-relative offset and
the 8-bit branch displacement from the currently open location to
address a. If the value k precedes 0, this command calculates and
displays the PC-relative offset and the 8-bit branch displacement
from the specified address a to the specified address k.

P or kP

Command that causes the user program to execute from the current
breakpoint location and stops when the next breakpoint location is
encountered or the end of the program is reached. If the value k is
specified, ODT continues with program execution from the current
location and stops at the breakpoint only after encountering it the
number of times specified by integer k.

Quantity register indicator. Represents the contents of register $Q
(quantity register).

Command that sets all relocation registers to the highest address
value, 1777778, so that they cannot be used in forming addresses.

Command that sets relocation register n to the highest address value,
1777778, so that it cannot be used in forming addresses.

a;nR

Command that sets relocation register n to address value a. If n is
omitted, ODT assumes relocation register O.

5 or nS

Command that executes one instruction and displays the address of
the next instruction to be executed. If n is specified, ODT executes
n instructions and displays the address of the next instruction to be
executed.

Command that sets the current mode of ODT to user mode.

Command that 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 Table 5-2 for a discussion
of the SST vector registers and the $nV/ command.)

ODT Characters and Symbols

2-9

Table 2-3 (Cont.):

OOT Operators and Commands

Format

Meaning

WorkW
orm;W
or m;kW

Command that searches 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 that match those of
the search argument specified in the search argument register ($A).
OOT compares each memory word and the search argument for
equality under the mask specified in the search mask register ($M).
Only bit positions set to 1 are compared. When a match occurs,
OOT displays 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 OOT initiates the search.

Command that causes OOT to exit and returns control to the
Executive of the host operating system.

Command that sets the current mode of OOT to supervisor mode.

2-10 ODT Characters and Symbols

Chapter 3
Controlling Program Execution with ODT
When you run a task image into which the On-Line Debugging Tool (ODT) has been linked,
ODT takes control before the first instruction of the task is executed. Information about the
task is stored in ODT's internal registers, as described in Section 5.2.
At this point, you can execute your task immediately or issue ODT commands that affect
locations or registers.

3. 1 Setting and Removing Breakpoints
A common method of using ODT is to set breakpoints at important points in the task and then
execute the task. When a breakpoint is reached, execution is suspended. You can examine
locations or registers to see how your task is executing. You can then change elements of your
task and see how the changes affect execution.

3.1.1 Setting Breakpoints
To set a breakpoint at a location, issue a B (Breakpoint) command.
Breakpoint Command Format

a;nB
Parameters

a
Specifies an address expression (in any of the forms described in Section 2.2) representing
the location at which the breakpoint is to be set. This location must always be the first
word of an instruction.

n
Specifies the number of the breakpoint address register (from 0 to 7) to be used to store the
address of the specified location. If you omit n, breakpoint address registers are assigned
sequentially, beginning with register O.

Controlling Program Execution with ODT 3-1

You can also set a breakpoint by opening a breakpoint address register as a word location and
changing its contents. The address of a breakpoint address register is its register name, $nB.
Opening and changing the contents of word locations is described in Chapter 4. Registers are
described in Chapter 5.
In RSX-llM-PLUS and MicrojRSX systems that use separate instruction and data space
breakpoints, always refer to instruction space, regardless of which space you referred to when
you set the breakpoints. When a debugging session begins, you automatically access instruction
space. You access data space by entering the D command; you return to instruction space by
entering the I command.
Each breakpoint address register is associated with a mode indicator that shows whether the
breakpoint occurs in user or supervisor mode; this mode indicator depends on the mode in
effect at the time the breakpoint is set. You set supervisor mode by entering the Z command;
you return to user mode by entering the U command.

3.1.2 Removing Breakpoints
You can clear breakpoint address registers (and thus remove breakpoints) by using the
nB command, where n represents the number of the register. If you omit n, all breakpoint
address registers are cleared. You can also clear a breakpoint and reset it by specifying a new
address expression for a breakpoint address register. The a;nB command allows you to specify
a new address expression.
The following example shows how breakpoints are set, cleared, and reset:
_B
_1020 ;B
_2030;B
_3040;B
_4050;B
_2032;1B
3B

At the end of this example, breakpoint address register 0 is set to location 1020, breakpoint
address register 1 is set to 2032, and breakpoint address register 2 is set to 3040. Breakpoint
address register 3 is clear.
Note that ODT immediately generates a carriage return, a line feed, and a new prompt when
you type the letter B.
You can also clear a breakpoint register by opening it as a word location whose address is $nB
and changing its contents, as described in Chapter 4.

3-2 Controlling Program Execution with ODT

3.2 Beginning Task Execution
To begin executing your task, type the G (Go) command. At the G command, the following
takes place:

..
..
..

The task's starting address is returned to the program counter (PC) from the ODT general
register in which it was stored.
The task's stack and other general registers are restored .
The contents of each location at which a breakpoint was set are swapped with the
contents of the corresponding breakpoint instruction register. (These registers, described in
Section 5.2, are initialized by ODT-to-BPT instructions.)
The task begins executing.

The task continues to execute until it reaches one of the following:

..
..

A breakpoint
An error of type BE, EM, FP IL, 10 MP OD TE, or TR (described in Appendix A)
1

The end of the program
Once the task is executing you cannot stop it except by aborting and then restarting it.
(RSX-llM-PLUS and Micro/RSX systems include commands to reenter an interrupted program,
as described in Section 1.5.1.)
l

When the task reaches a breakpoint ODT executes the BPT instruction that was swapped into
the breakpoint location. At the BPT instruction the following takes place:
l

Task execution is suspended.

The contents of the user task general registers are stored in ODT internal registers.

The original contents are restored to all breakpoint locations from the breakpoint instruction
registers where they have been stored.

ODT issues a message indicating that a breakpoint has been reached. This message has the
format nB:a, where n is the breakpoint address register number and a is the location of the
breakpoint that was stored in that register.

ODT issues its prompt.

While task execution is suspended, you may issue any ODT command.

3.3 Continuing Task Execution
You can continue task execution by typing the P (Proceed) command, the G command, or the
aG command. The task continues executing until it reaches a breakpoint, one of the errors
specified in Section 3.21 or the end of the program.
Use the P command to continue execution after a breakpoint. When you type P, the contents
of the user general registers are restored, the BPT instructions are swapped into all breakpoint
locations, and task execution resumes at the instruction following the last logical instruction
executed. If execution stopped because of a breakpoint, it will resume at the breakpoint
location. If execution stopped because of an error, it will resume at the location following the
error location, not at the error location itself.

Controlling Program Execution with ODT 3-3

You can resume execution by using the G command. However, because the G command does
not transparently restore the breakpoint instruction, you should not use it to resume execution
after a breakpoint.
To resume execution at a specific location, use the aG command. The argument a is an address
expression representing the task location. The address specified must correspond to a word
location boundary, that is, an even location. Registers are affected as described in Section 3.2.
Execution begins at the specified location.
Note that you can use only G or aG to begin execution of a task. If you type P when no G
command has been executed, ODT responds with a question mark (?) and a new prompt.

3.4 Using the Breakpoint Proceed Count
If you set a breakpoint inside an execution loop, you may want to suspend execution only when
the loop has been executed a certain number of times. You can specify how many times a loop
should be executed by including a breakpoint proceed count with the P command, in the form
kP. The loop is executed k-l times; execution is suspended when the breakpoint is reached for
the kth time.

The kP command is associated only with the breakpoint that has most recently occurred. The
count k is stored as an octal value in a breakpoint proceed count register ($nG), where n is a
number corresponding to the number of the appropriate breakpoint address register.
You can examine the breakpoint proceed count registers, or set them directly, at any time
following the procedures for examining and setting word locations described in Chapter 4.
These registers are all initialized by ODT with the value 1. If you change the value of a register,
the new breakpoint proceed count will be used when the breakpoint is next encountered as a
result of the P command.

3.5 Stepping Through the Program
You can use the S (Step) command as another method for executing a task in stages. With this
command, you can execute user task instructions one at a time or several at a time.
The command has the format nS, where n is the number of instructions that ODT should
execute before suspending execution. The default value of n is 1.
When n instructions have been executed, ODT suspends task execution and prints a message
of the form 8B:a, where a is the location of the next instruction to be executed. (The format of
a is relative by default, as explained in Chapter 4.) ODT then prompts for another command.
The S command is implemented through the T-bit (trace bit) in the Processor Status Word (PSW)
(see Appendix B). The T-bit is set when you issue the command. When the nth instruction is
executed, control is returned to the task.

3-4 Controlling Program Execution with ODT

The following example shows ODT's response to the program execution commands described
in this chapter:
_1.1052;B
_1.2052; IB
_G

OB : l.001052

-P

IB : l.002052

8B : l.002056
_5

8B:l .002062

3.6 Setting Breakpoints in Overlay Segments
When debugging overlaid tasks with ODT, you cannot set a breakpoint in an overlay segment
that has not been loaded into memory. ODT sets the breakpoints in memory only. It does
not change the disk image of the task being debugged. So, if you set a breakpoint in the
range of memory addresses that the overlay will occupy before it has been loaded into memory,
the breakpoint will be overwritten when the overlay is actually written. In the same way,
breakpoints in an overlay segment are lost once the segment is overwritten by a different
overlay segment.
You can, however, set a breakpoint in the overlay run-time routines so that you receive control
after an overlay has been loaded, but before it is executed. If you set a breakpoint at global
symbol $ALBP2 in your task, you will receive control each time an overlay is loaded into
memory from disk and before the overlay is executed. Doing so enables you to put breakpoints
in the overlay segment.
With this method, your task will breakpoint on every overlay load. Because you will probably
only be interested in debugging one particular overlay segment, you must keep track of the
sequence and number of overlay loads to know when the overlay segment that you are
interested in has been loaded. Or, if there is a unique location in the overlay segment that
you are interested in, you can merely examine the corresponding memory location in your task
each time an overlay is loaded until the contents of the memory match the value in the overlay
segment. Then you know that the segment has been loaded.
A breakpoint at a second location in the overlay run-time routines, $ALBPl, will give you
control every time control is transferred to an overlay that is already resident in memory and
that does not have to be loaded from disk. This breakpoint location is generally less useful
than the first.
Because the global symbols $ALBPI and $ALBP2 are defined in the system library routine, they
are not included in a task's map file by default. To include these global symbols in your map
file, build your task with the Task Builder (TKB) jMA switch (if your eLI is MeR) or with the
LINK command j5Y5TEM_LIBRARY_DI5PLAY qualifier (if your eLI is DeL).

Controlling Program Execution with ODT 3-5

Chapter 4
Displaying and Altering the Contents of Locations
with ODT
During an OOT session, you can alter the contents-either instructions or data-of locations in
your task. To alter the contents of a location, you must first open the location.
You open a location by displaying its contents. To display a location's contents, use any of the
commands described in Sections 4.3 to 4.9. The contents displayed are automatically placed
into the quantity register ($Q).
OOT displays a location by showing the address, a mode operator (either word mode or byte
mode, depending on the size of the location opened), and the contents of the location. The
format in which the location is displayed is controlled by the contents of the format register
($F), as described in Table 5-1. By default, OOT displays addresses in relative form whenever it
has both the number of the relocation register containing the bias value closest to (but less than)
the address and the relative location of the address from that value. When this information
is not available, OOT prints the address in absolute form. (Relative and absolute forms are
described in Section 2.2.1.)
OOT does not generate a carriage return or line feed after displaying the contents of a location.
Until the location is closed, the cursor remains on the same line, wrapping as necessary.

4.1 Altering the Contents of a Location
You alter the contents of a location by typing the new contents immediately after the displayed
contents. The new contents can be an absolute octal value (of up to six digits) or an expression
equivalent to a 6-digit octal value, as described in Section 2.2.2. If you enter an octal value,
you may omit leading zeros.
In the following examples, the value 1234 8 is substituted for the value 1234568 in the location
represented by the address expression 2,0. The value 1774268 (the two's complement of
the expression 16-370) replaces the value 000000 in the location represented by the address
expression 4,10.
_~.0 1t 23456 1234

_4.10/000000 16-370

Displaying and Altering the Contents of Locations with ODT 4-1

After you have altered the contents of a location, you can verify the new contents by displaying
them in a variety of modes. Use the commands described in Section 4.11 to display the contents.
These commands do not close the location. You can also display, and thus verify, the new
contents by closing the location and then reopening it.
Note that you must close the currently open location before you can alter the contents of a new
location.

4.2 Closing a location
To close one location without automatically opening another location, enter the RETURN
command (by pressing the RETURN key). This command has no effect on aDT when no
location is open.
Entering the RETURN command generates a carriage return/line feed combination. aDT then
prompts for another command, as follows:
_1.200/450123 [BTIJ

To close one location and automatically open another location, you can use any of the following
commands, which are described in Sections 4.4 to 4.9:
>

4.3 Opening Word and Byte locations
aDT interprets the slash character ( / ) as a word mode octal operator and the backslash character
(\) as a byte mode octal operator. Using these operators in aDT commands provides the most
direct way to open word and byte locations.

You can also open word and byte locations and display their contents in American Standard
Code for Information Interchange (ASCII), or you can open and display words in Radix-50.
These modes are described in Section 4.11.

4.3.1 Opening Word and Byte Locations at a Specified Address
To open a word location beginning at an address, in response to the aDT prompt, type an
address expression corresponding to that address, followed by a slash (a/). The address must be
even numbered. aDT opens the word location beginning at the specified address and displays
the contents of that location as a 6-digit octal number.
To open a byte location, type an address expression corresponding to an odd- or even-numbered
address, followed by a backslash (a\). aDT opens the byte location beginning at the specified
address and displays the contents of that location as a 3-digit octal number.
The following examples show the effects of the a/ and a\ commands:
_1000/ 012675 ITillJ
_1001\ 025 IRET!

4-2 Displaying and Altering the Contents of Locations with ODT

4.3.2 Reopening the Location Last Opened
You can use the word mode and byte mode octal operators without address arguments to
reopen the location last opened. The slash (/) command opens the word location last opened
and displays the word at that location. The backslash (\) command opens the byte last opened
and displays the contents of that byte. (If the last location opened was a word, the byte opened
and displayed is the low-order byte of that word.)
When no location is open, you can also use the circumflex (A) command to open the last-opened
location, as described in Section 4.5.

4.3 .3 Moving Between Word and Byte Modes
The word mode and byte mode octal operators establish word mode and byte mode, respectively.
Once you have opened a location using the word mode octal operator (/), all locations
subsequently opened will be octal words until the mode is changed. Once you have opened a
byte location using the byte mode octal operator (\), all locations subsequently opened will be
octal bytes until the mode is changed.
You can change from word mode to byte mode by opening a location with the a\ command
or by specifying an odd-numbered address as the value a in the a/ command. Subsequent
locations will be displayed as bytes until a word location is explicitly opened by using an evennumbered address as the value a in the a/ command (or the a" or a% commands, as described in
Section 4.11).
The following example shows a change from word mode to byte mode and back again using
an odd-numbered address in the a/ command. (The LINE FEED command, which opens the
next sequential location in whatever mode is currently in use, is described in Section 4.4.)
_1001/ 123 321 [RITJ
j 321 !ill

!ill
001003 \010 !ill
001004 \201 !Bill
001002 \021

_1006/ 102054

If a word location is open, you can examine its low-order byte by typing the byte mode octal
operator (\) immediately after the displayed contents of the location. The location remains
open and you remain in word mode. The following example shows this use of the byte mode
octal operator:
_1006/ 102054 \ 054

!ill

001010/012345

You can also examine words or bytes of an open location in ASCII or Radix-50 modes, as
described in Section 4.11.

Displaying and Altering the Contents of Locations with ODT 4-3

4.4 Opening the Next Sequential Location
To open and examine successive locations, use the LINE FEED command. (On VT200-series
terminals, a line feed is generated by pressing CTRLjJ. On VT100-series terminals, a line feed
is generated by pressing the LINE FEED key.) The LINE FEED command closes the currently
open location and opens the next sequential location. If the currently open location is a word,
the next sequential location will be opened as a word. If the currently open location is a byte,
the next sequential location will be opened as a byte.
If you specify a value before entering the LINE FEED command, that value replaces the contents
of the open location, as described in Section 4.1.

4.5 Opening the Preceding Location
To back up in your task and open the location preceding the currently open location, use the
circumflex (A) command. This command closes the currently open location. If the currently
open location is a word location, the command opens the word location immediately preceding
it. If the currently open location is a byte, the command opens the preceding byte.
A

If no location is currently open, the command opens and displays the contents of the lastopened location. The contents may be a word or a byte, depending on the mode currently in
effect.
A

If you specify a value before entering the
open location, as described in Section 4.1.

command, that value replaces the contents of the

The following example shows the use of the LINE FEED and commands. Location 232, relative
to the bias contained in relocation register 0, is opened as a word and its contents are altered.
In response to the LINE FEED and commands, ODT proceeds to the next word location and
then backs up to location 232 to display the new contents.
A

_0,232/005036 005046 [ill
0 ,000234 /012746 0,000232 /005046

4.6 Opening Absolute Locations
To proceed from an open location to the location whose address is contained in that open
location, use the at sign (@) command. This command closes the currently open location and
uses the contents of that location as the absolute address of the next location to be opened. You
can specify new contents for the original location by entering a value before the @ command,
as described in Section 4.1.
You can use the @ command only if the currently open location is a word.
Opening an absolute location does not necessarily mean that the location is displayed as an
absolute address. As shown in the following example, where relocation register 2 is set to
contain the bias value 370 (as described in Section 5.2.1), ODT by default still displays the
location as a relative address:
_370;2R
_2,600/ 012345 12746G
2,012356 /027117

Location 12356, relative to bias value 370, is equivalent to the absolute address specified, 12746.

4-4 Displaying and Altering the Contents of Locations with ODT

4 .7 Opening PC-Relative Locations
To open a location relative to the program counter (PC), use the underscore (_) command.
This command adds the contents of the currently open location to the value of the program
counter, which is the address of the currently opened location plus 2. ODT then closes the
currently open location and opens the location whose address is the result of its calculation. If
you enter a value before the _ command, this value replaces the contents of the open location
and becomes the value used in the calculation.
You can use the _ command only if the currently open location is a word.
If the currently open location contains an odd number (or if it contains an even number but is
already a byte location), so that the calculated address does not fall on a word boundary, the
_ command opens a byte at the location calculated.

The following examples show how the _ command is used:
_1000/000040 _
001042 /052407
_0,232/ 012345 _
0,012601 /041
_0,232/012345 123456_
0,123712 /020301

4.8 Opening Relative Branch Offset Locations
Use the right angle bracket (> ) command to open a location at a branch offset relative to the
currently open location. The offset is calculated as follows:
1.

The low-order byte of the contents of the currently open location is interpreted as a signed
value. A negative value results in a negative branch offset.

2. This value is multiplied by 2.
3. The resulting offset is added to the PC value, which is the address of the currently open
location plus 2.
The > command closes the currently open location and opens the location whose address is
the value calculated. Its effects are shown in the following examples:
_1,66/ 005046>
1,000204 /000601
_1032/000407 301>
000636 /000010

If you specify a value before entering the > command, the low-order byte of that word is used
in the offset calculation. The value replaces the contents of the open location, as described in
Section 4.1.

Displaying and Altering the Contents of Locations with ODT 4-5

4.9 Returning from a Calculated Location
If you have used any of the three address calculation commands described in the last three
sections (@, _, or > ) and wish to return to the location from which you began to calculate
addresses, use the left angle bracket ( <) command. This command closes the currently open
location and reopens the previous word.

The following example shows the use of the

< command:

_1036/ 021346 ~
001034/172543 101036_
102074 /000002 <
001034 /101036

If the currently open location was not opened by a @, _, or > command, the
simply closes and reopens the current location.

< command

4.10 Opening the Directive Status Word
Use the ODT internal register W to examine the Directive Status Word (DSW). Normally, task
memory location 46 contains the DSW. However, when using ODT, location 46 may reflect the
status from the last directive issued by ODT, and not the last directive issued by the task. ODT
register W always contains the correct DSW for the task.

4. 11 Using Different Output Modes
The examples in the previous sections showed ODT output in word mode octal and byte mode
octal. However, you can also use ODT to display the contents of locations in word or byte
mode ASCII and word mode Radix-50.
These modes follow the same rules as word mode octal and byte mode octal:

•

You can use the LINE FEED command to open succeeding locations in the same mode in
which the currently open location was opened.

•

You can enter any mode operator to display the contents of the currently open location in
another mode without changing the mode in effect or closing the location.

The interaction of mode operators was shown in Section 4.3.3, where a location opened in word
mode octal was examined in byte mode. The LINE FEED command that followed opened the
next sequential location in word mode octal.

4. 1 1. 1 ASCII Mode
ODT interprets the quotation mark character (") as a word mode ASCII operator and the
apostrophe ( ' ) as a byte mode ASCII operator. You open a location in word mode ASCII with
the a" command and in byte mode ASCII with the a' command.
If you open a location in any mode and then type a word mode ASCII operator, the contents
of the open location are displayed as two ASCII characters, but the location is not closed.
If you open a location in any mode and then type a byte mode ASCII operator, the contents of
the low-order byte of the open location are displayed as one ASCII character. The location is
not closed.

4-6 Displaying and Altering the Contents of Locations with ODT

The following examples show these uses of the ASCII operators:
_O,440" AB
_2,100' H
_0,232/034567 ' w "w9
0,000234/000123

_' S

!ill

mill

If you enter the word mode ASCII operator to examine the contents of a location, and the
location is aligned on a byte boundary (an odd-numbered address), ODT does not return an
ASCII character. Instead, it displays the contents of the location in the mode currently in effect,
as follows:
0,000235\ 025 " 025

4.11.2 Radix-50 Mode
ODT interprets the percent sign (%) as a word mode Radix-50 operator. (There is no byte
mode Radix-50 operator because Radix-50 is a method of fitting three characters into a word
and cannot be used in smaller units.)
You can use the Radix-50 operator to open locations. The a% command opens the location
specified in the address expression a and displays its contents as three Radix-50 characters.
The % command reopens the last-opened word and displays its contents as three Radix-50
characters.
If a word location is open, you can enter the % operator to examine the Radix-50 contents of
that location without closing the location.

The following examples show these uses of the word mode Radix-50 operator:
.4,232% IG1
4,232/ 034567
_%IG1

!Bill

_4,000232/ 034567 %IG1

Like the word mode ASCII operator, the Radix-50 operator cannot be used to interpret values
that begin on byte boundaries. If you enter the Radix-50 operator when the currently open
location has an odd address, ODT simply displays the byte value in the current mode.
Remember that you must enter new contents for a location as an octal value or an expression,
not as Radix-50 characters. To determine the octal equivalent of Radix-50 characters, use the
Radix-50 evaluator ( *), as described in Section 7.3.5.

Displaying and Altering the Contents of Locations with aDT 4-7

Chapter 5
Using Registers in OOT
The On-Line Debugging Tool (ODT) has a number of 16-bit registers. Some of these registers
are used for temporary storage of values. Some contain values used repeatedly throughout the
execution of your task under ODT. All the registers are word locations that you can examine
and alter.
Each ODT register has a unique name beginning with a dollar sign ($). The $ and the character
or characters that follow it make up an address expression that identifies the register.
This chapter explains how ODT uses its registers. Tables 5-1 and 5-2 summarize the registers
and are useful for quick reference.

5. 1 General Registers
ODT has eight general registers, numbered $0 to $7, which store the contents of the user
program's general registers when ODT has control. These registers are automatically set when
ODT is first invoked and when a breakpoint occurs. They can also be set by the user.

5. 1. 1 Examining and Setting General Registers
To examine a general register, enter the register name as the address expression in the ai, a",
or a% command. For example, you can enter any of the following:
$7/
$3%
$1"

ODT opens a register like any other word location. You can then alter the contents of the
register or use any of the following commands, as described in Chapter 4:
[Bill [ITlI-_Cil"%>' \

ODT treats the general registers as sequential word locations.

Using Registers in ODT 5-1

5 . 1.2 Contents of General Registers
When you issue the RUN command and ODT initially gains control, information about the user
task is stored in the general registers as follows:

Contents

Task's entry-point address

First three characters of task's run-time name (Radix-50)

Last three characters of task's run-time name (Radix-50)

$3-$4

Version number of user task if the program included the .IDE NT directive;
otherwise, the version number of ODT

When a breakpoint occurs, ODT's general registers store the contents of the task's general
registers.

5.2 aDr Internal Registers
The ODT internal registers store values for use during a debugging session. For example, they
store the locations of breakpoints and the memory limits to be used in search operations. Each
register is a 16-bit location that you can open by specifying the register name as the address
expression with any ODT command that opens a word location. You can enter any of the
following:
$3R/
$A"
$C%

It is rarely useful to examine an internal register in American Standard Code for Information

Interchange (ASCII) or Radix-50 mode.
You can alter the contents of these registers as you would the contents of any word. However,
this is not recommended in some cases, as noted in Tables 5-1 and 5-2.
Ten of the ODT internal registers are single registers; that is, there is only one register for
each function. You refer to one of these registers as $x, where x is an alphabetic character.
Table 5-1 lists these registers in alphabetical order. In the task, they appear in the order listed in
Table 2-3, that is,
$S $W $A $M $L $H $C $Q $F $X

You can access these registers as sequential word locations in this order, as in the following
example:
_$S/ oooooo [ill
$W /000001 [ill
$A /000000 [ill
$M /177777

5-2 Using Registers in aOT

Table 5-1:

CDT Single Registers

Function

Search argument register. You set this register to a word search argument by
opening with the j operator, or you can set to a byte search argument by opening
with the \ operator. It can also be set using the memory commands described in
Chapter 6.

Constant register. The 16-bit value in this register can be used as an address
expression or a value through the constant register indicator C, as described in
Sections 2.2.2 and 7.3.3.

Format register. When this register is set to 0, ODT displays all user task addresses
in relative form if an appropriate bias value is available in one of the relocation
registers. When this register is set to any other value, ODT displays user task
addresses in absolute form. See Section 2.2.1 for a description of absolute and
relative forms of addresses.

High memory limit register. The location contained in this register is the upper
location limit for ODT search, list, and fill memory operations. It is initialized
to O.

Low memory limit register. The location contained in this register is the lower
location limit for ODT search, list, and fill memory operations. It is initialized
to 0.

Search mask register. You set this register to a word search mask by opening with
the j operator, or you can set to a byte search mask by opening with the \
operator. It can also be set by arguments specified with the memory commands
described in Chapter 6. It is initialized to -1, 1777778 ,

Quantity register. ODT sets this register to the last value displayed, as described
in Section 7.3.4. $Q is also used for the results of expression calculations using
the = operator.

Processor status register. This register stores the Processor Status Word (PSW)
(see Appendix B) resulting from the last instruction executed prior to a breakpoint.
Users do not normally change the contents of this register directly.

Directive Status Word register. This register contains the Directive Status Word
(DSW) of the task, which indicates the success or specific cause of rejection of
the most recently executed directive. The contents of this register are maintained
across breakpoints. Always use this register to examine the DSW. The contents
of memory location 46 do not reflect the correct DSW for the task. See the
RSX-llM-PLUS and MicrojRSX Executive Reference Manual for details on the DSW.

Reentry vector register. A positive value in this register causes aDT to retain the
register values for successive entries of ODT, as described in Section 5.2.2.

The other ODT internal registers are grouped into sets of eight or three sequential word locations.
The integer n is part of the register name, in the form $nx; you must always include n, even if
its value is O.

Using Registers in ODT 5-3

Table 5-2 lists the register sets alphabetically. In a task, they appear as sequential word locations
in the order listed in Table 2-3, that is,
$nB

$nG

$nI

$nR

$nV

$nE

$nD

Table 5-2:

OOT Register Sets

Range of
n

$nB

0-7

Breakpoint address register n. This register contains the user-specified
address of location (breakpoint) in the user task whose contents are to be
swapped with the contents of $nI when a G or P command is executed.
A ninth register, $8B, is used by OOT for single-step execution.

$nO

0-2

Oevice control LUN (logical unit number) register n. As described in
Section 6.1.4, register $00 contains the LUN of the user terminal, and
register $10 contains the LUN of the console device. Register $20 contains
the QIO event flag number, normally a default value of 000034 8 .

$nE

0-2

SST stack contents register n. The top three items on the user program
stack are placed into these registers when a synchronous system trap (SST)
occurs. Stack contents depend on the type of trap taken, as explained in
the RSX-llM-PLUS and Micro/RSX Executive Reference Manual.

$nG

0-7

Breakpoint proceed count register n, where n corresponds to breakpoint
address register n. This contains the number of times the breakpoint
location should be encountered before the breakpoint is recognized. Each
register is initially set to 1 and can be set through the kP command (see
Section 3.4) or by opening $nG and altering its contents. A ninth register,
$8G, is used by OOT for single-step execution.

$nl

0-7

Breakpoint instruction register n. This register is initialized to contain a
BPT instruction, op code 000003, which is swapped with the contents of
register $nB when the G or P command is executed. The functions of the
BPT instruction are described in Section 3.2. A ninth register, $81, is used
by OOT for single-step execution.

$nR

0-7

Relocation register n. This contains the relocation bias of a relocatable
object module, which enables OOT to display user task addresses in
relative form if $F is set to 0 (see Table 5-1). OOT initializes each register
to 1777778 ,

$nV

0-7

Synchronous System Trap (SST) vector register n. This contains the entrypoint address of the OOT routine for handling a SST. If both OOT and the
user program have SST vectors enabled for the trap, OOT automatically
receives the trap, except for vector 6 ($6V), which must be explicitly
enabled through the V command (see Table 2-3). OOT handling of a
trap can be disabled by clearing the register; the user program vector then
receives the trap. Registers correspond to traps as follows:

5-4

Function

Using Registers in ODT

Table 5-2 (Cont.):

OOT Register Sets

Range of
Register

Function

SST Vector

$OV

Odd address reference in word instruction (also, on some
processors, illegal instruction executed)

$1V

Memory-protection violation

$2V

T-bit (trace bit) trap or BPT instruction executed

$3V

lOT instruction executed

$4V

Reserved or illegal instruction executed

$5V

Non-RSX-ll EMT instruction executed

$6V

TRAP instruction executed

$7V

POP-ll/40 floating-point exception error

The following sections describe the functions of OOT internal registers $nR and $X in greater
detail. The OOT internal registers $C, and $Q are described in Chapter 7. Registers used in
memory operations ($L, $H, $M, $A, and $nO) are described in Chapter 6.

5.2. 1 Relocation Registers
OOT's eight relocation registers allow you to refer to locations by relative addresses instead
of absolute addresses. Since relative addresses are easy to determine from source file listings,
using them makes debugging faster and simpler.
When OOT is initialized, each relocation register is set to 1777778 , This is the highest possible
memory address and therefore cannot be used in constructing address expressions. To make a
relocation register useful, you place in it the base address of a relocatable module or another
convenient point, as explained in Section 2.2.1. This address functions as a relocation bias that
is added to the relative address in an address expression to form the absolute address of a
location.
You obtain the base (starting) address of a module by consulting the memory allocation synopsis
in your task map. This part of the map gives the octal starting address of each program section
and each module that makes up a program section. It also shows the extent of the module, in
octal and decimal.
The following figure shows a memory allocation synopsis for a brief task:
SECTION

TITLE

IDENT

FILE

BLK. : (RW,I,LCL,REL,CON) 001264 001012 00522.
001264 000574 00380.
$$RESL:(RO,I,LCL,REL,CON) 010152 000112 00074.
$$$ODT:(RW,I,GBL,REL,OVR) 002276005654 02988.
002276 005654 02988.

HIYA

HIYA.OBJ;l

ODTRSX M06

ODT.OBJ;l

Using Registers in ODT 5-5

5.2. 1. 1 Setting Relocation Registers
You can set relocation registers either by opening them as word locations and altering them, or
you can set them by using special aOT commands that affect relocation registers.
To open a relocation register as an octal word, use the register name $nR as the address
expression a in the aj command (or any of the other commands described in Chapter 4 that
open words). You can enter a new value for the register after examining the existing contents.
The aOT command a;nR sets register $nR to the location specified as address expression a. If
you omit n, register $OR is assumed.

5.2. 1.2 Clearing Relocation Registers
To remove a relocation register from consideration in calculating addresses, enter the nR
command, where n is the number of the relocation register. This command sets the register to
1777778, so that it is no longer useful in constructing address expressions. If you omit n, all
relocation registers are set to 1777778 ,

5.2.2 The Reentry Vector Register
If you have fixed a task in memory (see the FIX command in the RSX-llM-PLUS MeR Operations

Manual), you can use the reentry vector register, $X, to maintain register values set during your
debugging session and to keep track of your access to the task.
The reentry vector register contains the value -1 when your task is built. When you execute
the task for the first time, the register value is incremented to O. The 0 value causes aOT to
omit the task name from the invocation message line (described in Section 1.3) the next time
you enter the task. This omission indicates that the task is fixed in memory.
If you intend to reenter the task for further debugging, you should set $X to 1 or another

positive nonzero value. As long as the value of $X is positive and nonzero, the fixed task
is reentered at the value stored in $7 (the program counter), and the values stored in aOT's
registers are maintained. You can continue to debug the task using the breakpoints, constants,
and other values established in an earlier debugging session. If $X is not positive, all registers
are initialized when you reenter the task.
You can use the reentry vector register as a counter to record how many times you have entered
a fixed task. To do this, set the register to 1 the first time you enter your task and increment it
each time you enter the task again.

5-6

Using Registers in ODT

Chapter 6
Memory Operations in ODT
The On-Line Debugging Tool (ODT) allows you to perform three kinds of operations on blocks
of memory in your task:
III

Search memory for bit patterns or references to locations

Fill memory with a value

List blocks of memory on an output device

Section 6.1 describes how to establish the registers used in memory operations. The subsequent
sections of this chapter describe how to use ODT commands to perform these operations.

6. 1 Registers Used in Memory Operations
ODT memory operation commands function between limits in memory that you must specify.
Search and fill commands require an argument to be searched for or deposited. Search operations
also require a search mask.
aDT maintains registers to contain all these values. You can set these registers as word or
byte locations (as described in Chapters 4 and 5) before issuing memory operation commands.
You can also specify a search argument and a search mask as the k and m arguments in the
commands themselves. If you do not specify an argument in one of these commands, ODT uses
the current contents of the appropriate register. If you do specify an argument, that argument
replaces the contents of the register.

Memory Operations in ODT 6-1

6. 1. 1 Search Limit Registers
There are two search limit registers: $H, which contains the high memory limit for a search,
fill, or list operation; and $L, which contains the low memory limit. You deposit a memory
location in one of these registers by opening it as a word location and changing its value to
the address of the location. You can specify the location in either absolute or relative form, as
follows:
_$L/ OOOOOO 1000 [gffi
j
001000 2.4060 [ill
_$H/OOOOOO 3,100

[gffi

If the value in $L is greater than the value in $H, OOT does not perform the memory operation
requested using these registers. Instead, OOT displays its prompt.

6. 1.2 Search Mask Register
OOT initializes the search mask register $M to 177,7778, so that all bits are set to 1. You set the
value of the register by opening it as a word location and changing its value. Only bit positions
set to 1 in the search mask are compared in the search operation. The value compared is that
set for the corresponding bit position in the search argument register $A.
You can also set register $M by specifying a value m, followed by a semicolon (;), in any of
the search commands described in Section 6.2.

6.1.3 Search Argument Register
The search argument register $A contains the value searched for in a memory search operation
or filled with in a memory fill operation. To set this value, open register $A as a word or byte
location and change its contents, or specify the argument k in one of the search commands
described in Sections 6.2 and 6.3.
As noted in Section 6.1.2, only bit positions set to 1 in the search mask are compared in any
memory search operation.

6. 1.4 Device Control LUN Registers
The device control LUN registers $00 and $10 contain the logical unit numbers of the user
terminal (TI) and the console device (CL), respectively. You specify one of these registers as the
value n in the n;a;kL command (see Section 6.4.1) to indicate what device should be used for
a listing. The device control LUN register $20 contains the event flag number, which is 348 by
default. Unlike the values for registers $00 and $10, the TKB option GBLPAT cannot override
the value for register $20. See Section 1.2.4 for more information on changing the values of
the registers $00 and $10.

6.2 Searching Memory
There are three memory search commands: W, N, and E. Each of these commands has several
forms, depending on the number of registers that already contain values that you want to use
in the search operation. The following sections describe these command forms.

6-2 Memory Operations in ODT

6.2. 1 Searching for a Word or Byte
The W command searches for occurrences of the search argument (comparing bit positions
specified in the search mask) within the range set by the contents of the search limit registers.
The full form of the command is m;kW, where m specifies the search mask and k specifies the
search argument. However, you can omit either or both of these arguments if the corresponding
registers contain the values that you want to use. If you omit m, you should also omit the
semicolon argument separator.
ODT performs an exclusive OR (XOR) operation on the contents of each location and the search
argument; it then ANDs the result of this comparison with the search mask. A result of zero
indicates a match. When a match occurs, ODT prints the address and contents of the location
and repeats the search operation until the high memory limit is reached.

6.2.2 Searching for Inequality of a Word or Byte
The N command is the opposite of the W command. It examines the search range for words or
bytes that do not exactly match the search argument in the positions determined by the search
mask.
The full form of the command is m;kN, where m specifies a search mask and k specifies a
search argument. As with the W command, you can omit either or both of these arguments.
The search algorithm proceeds like that for the W command, except that ODT only displays a
location's address and contents when the AND operation has resulted in a nonzero value.

6.2.3 Searching for a Reference
The E command searches for memory locations containing instructions whose execution results
in a reference to the task address specified as the search argument. Because the search argument
represents an address, it can only be a word, not a byte.
The full form of the command is m;kE, where m represents the search mask and k the search
argument. You can omit either or both of these arguments if you want to use the values already
contained in registers $M and $A. For effective use of the E command, the search mask should
be set to 177,7778, so that all bit positions are compared.
ODT compares each location within the search limits and displays the address and contents of
locations that contain any of the following:
•

The search argument as an absolute address

•

A relative address offset reference to the absolute address specified as the search argument

•

A relative address branch reference to the absolute address specified as the search argument

Memory Operations in ODT 6-3

6.3 Filling Memory
The F command fills the block of memory defined by the high and low memory limit registers
with the value in the search argument register. To set this register, use the command $A/ (see
Section 6.1.3), or specify the argument k with the F command in the form kF.
If the last location opened was a word, the memory range is filled with words. If the last
location was a byte, the memory range is filled with bytes. The low-order byte in register $A
is used.

In the following example, word locations 1000 to 1776 are set to 0, and byte locations 2000 to
2777 are filled with American Standard Code for Information Interchange (ASCII) spaces (40 8 ):
_1000; 1R
.-2000;2R
_3000;3R
_$L/'OOOOOO 1,0 mill
_$H/OOOOOO 2, -2 mill

_OF

_$L;'00 1000 2,0 mill
_$H/ 001776 3,-1 mill
_SA \ 000 40 mill

6.4 Listing Memory
The L command lists on an output device the block of memory defined by the high and low
memory limit registers. The following sections describe how you request a listing and what the
listing looks like.

6.4. 1 Command Format
The L command has the format shown next.
Listing Memory Command Format

n;a;kL
Parameters
n

Specifies the device control LUN register number for the listing operation. A value of 0
indicates the user terminal (TI). Any other value is interpreted as 1 and indicates the console
listing device (CL). The default is O.

a
Specifies the low memory limit for the listing operation. If you omit a, the value of register
$L is used. If you specify a, that value is placed in $L.
k

Specifies the high memory limit for the listing operation. If you omit k, the value of register
$H is used. If you specify k, that value is placed in $H.

6-4 Memory Operations in ODT

You must include the semicolon argument separator (;) between a and k if you specify the
argument a. You must include two semicolons if you specify the argument n.

6.4.2 Listing Format
A memory listing is formatted in groups of eight units. Each line begins with a location, in
relative form if possible (see Section 2.2.1), followed by eight words or eight bytes in the
current output mode. A memory listing is displayed in whatever mode was used to open the
last opened location. Thus, you can list blocks of memory in word mode octal, byte mode octal,
word mode ASCII, byte mode ASCII, or word mode Radix-50, as described in Section 4.11.
The following example shows the output displayed on the output device in response to various
listing commands. Note in this case that the question mark (?) displayed in response to
the command is not OOT's error indicator. It is merely the ASCII character stored in the next
byte.
I

Example 6-1:

OOT Listing Format

_ 1344; 1400L
001344 /047503 046125 020104 020111 040510 042526 054440 052517
001364 /020122 040516 042515 050040 042514 051501 037505
_1344" CO L
001344 "CO UL D I HA VE Y au
001364 "R NA ME P LE AS E?
_1344\ 103 L
1344 \103 117 125 114 104 040 111 040
1354 \110 101 126 105 040 131 117 125
1364 \122 040 116 101 115 105 040 120
1374 \114 105 101 123 105
_1344' C L
001344 'C a U L D I
001354 'H A V E YOU
001364 'R
N A ME P
001374 'L E A S E
, ?

_1300;R
_$H/001400 0,101
_1344' C L
0,000044 'C a U L D I
0,000054 'H A V E YOU
0,000064 'R
N A ME P
0,000074 'L E A S E ?

Memory Operations in ODT 6-5

Chapter 7
Performing Calculations in ODT
The On-Line Debugging Tool (ODT) performs a variety of arithmetic calculations useful in
determining offsets, Radix-50 equivalents, and other values. This chapter describes commands
that perform these calculations. Section 7.1 explains how to calculate relocatable addresses;
Section 7.2 explains how to calculate offsets; and Section 7.3 describes how to evaluate
expressions.

7. 1 Calculating Relocatable Addresses
If you know the absolute (relocated) address of a location and want to determine its relative
address, or what relocation register contains the closest base address, use one of the forms of
the a;nK command.
If you specify both a, the absolute address, and n, a relocation register, in the a;nK command,
ODT calculates and displays the relative address, as follows:
_4000;2K =2,001460

Note that the equal sign (=) is part of ODT's response, not part of the command that you enter.
If you 9mit n, ODT uses the relocation register whose contents are closest to (but less than) the
~9solute address specified.
If you omit a, ODT assumes the address of the last location opened. You should omit the
semicolon (;) argument separator if you omit a.

To determine the absolute address of an open location or of the last-opened location, enter a
period (.) (current location indicator) followed by an equal sign (expression evaluation operator),
as described in Section 7.3.2.

Performing Calculations in ODT 7-1

7.2 Calculating Offsets
The 0 (Offset) command calculates and displays the program counter (PC) relative offset and
the branch displacement from one location to another.
There are two forms of this command. The aO command calculates the offset from the currently
open location to the location represented by address expression a. This form of the command
can be used only when a location is open; you type it on the same line as the displayed contents
of the open location.
The a;kO command calculates the offset from the location represented by address expression a
to the location represented by address expression k. (In this case, k can have any of the address
expression forms described in Section 2.2.) This command can be entered either on the same
line as an open location or on a separate line, in response to the ODT prompt.
The 0 command (in either form) calculates either positive or negative offsets. Negative offsets
are displayed in two's complement form.
ODT displays the PC-relative offset and the branch displacement as 6-digit octal numbers. The
PC-relative offset is preceded by an underscore (_) and followed by a space. The branch
displacement is preceded by a right angle bracket ( > ), as shown in the following example:
_1034/103421 10460 _000010 >000004

A location that is open when you use the aO or a;kO commands remains open after the
offset and branch displacement are displayed. You can perform another calculation, change the
contents of the location, or enter any ODT command that affects an open location.
Offsets can be calculated in either instruction or data space.

7.3 Evaluating Expressions
You can evaluate expressions during your debugging session by using the techniques described
in the following sections. To evaluate an expression while a location is open, enter the evaluation
command on the same line as the displayed contents of the location. ODT places the results of
its evaluation into the $Q register. To replace the contents of the open location, you enter Q
or the value of the expression. You can also evaluate expressions when no location is open by
typing the evaluation command in response to the ODT prompt.

7.3.1 Equal Sign Operator
To evaluate an expression, enter the expression followed by the equal sign ( = ). The expression
is converted to a 6-digit octal value, placed in the $Q register, and displayed. ODT truncates
the octal value of 16 bits when necessary.
Negative values are calculated, stored, and displayed in two's complement form. You can
specify a negative value either in two's complement form or with the minus sign ( -).
You can perform addition and subtraction within an expression to be evaluated. To add values,
include a plus sign (+) or a space between the values. To subtract values, include a minus
sign. ODT does not recognize parentheses or assign precedence to any operator. Expressions
are evaluated left to right.
An address expression, in relative or absolute form, can be all or part of an expression to
be evaluated.

7-2 Performing Calculations in ODT

You can include one of these three indicators in the expression: the current register indicator,
the constant register indicator, or the quantity location indicator. These indicators are described
in the following sections.
If you enter the equal sign without an expression to be evaluated, OOT evaluates the null
expression as zero and enters zeros in the $Q register.

The following examples show the evaluation of expressions using the equal sign. Relocation
register $OR contains the value 370. The constant register contains the value 40.
_0,0=000370
_0,16=406
_O,C=O00430
_0,16+16+2=0000426
_16-370=177426
_177777+16+16=000033
_-1+16+16=000033
_C 177777=000037
_232323=032323

7.3.2 Current Location Indicator
The current location indicator ( . ) represents the address of the currently open location. You use
this symbol to include the address of the currently open location as part or all of an expression
to be evaluated.
The following example shows how the current location indicator is used:
_320; lR
_1,10/000000 .+10=000340

7.3.3 Constant Register Indicator
The C indicator specifies the 16-bit value contained in the constant register, $C. You can set
this register to any value and use the indicator in place of any a or k argument in an OOT
command (as shown in Section 2.2). You change the value of C by opening the $C register as
a word location and changing its contents.

7.3.4 Quantity Register Indicator
OOT stores the last value that it displayed in the quantity register, $Q. When you open a
location, OOT stores that location's contents in the $Q register. If the location is a byte, the $Q
register contains that byte in its low-order byte and zeros in its high-order byte.
You can refer to this 16-bit value by using the quantity register indicator Q. The quantity
register indicator is especially useful for changing the contents of open locations and for setting
registers, as shown in the following examples:
_1342/173214 Q+10 [8ITI
j 173224 [8ITI
_$3/013624 Q; 5R [8ITI
_5,20/013644

Performing Calculations in ODT 7-3

7.3.5 Radix-50 Evaluation
To enter Radix-50 characters, you must know the numeric value of each Radix-50 word. A
Radix-50 word, as explained in Section 4.11.2, contains three Radix-50 characters. To determine
the value of the Radix-50 word, enter the numeric equivalents of the Radix-50 characters in
that word, separated by asterisks (*), as an expression to be evaluated. Follow the expression
with an equal sign, as shown in Section 7.3.1. aDT calculates a 6-digit octal value, places that
value in the $Q register, and displays it immediately after the equal sign, as follows:
33*24*12=125752

Note that you cannot evaluate Radix-50 characters in conjunction with any other evaluation
operation (addition, subtraction, or location calculation). You cannot use any other symbol (C,
Q, or .) in the expression to be evaluated.

If you specify the equivalents of only two Radix-50 characters, aDT fills the high byte of the
word with zeros, as necessary.
The Radix-50 character set includes all alphabetic and numeric characters (A to Z and a to 9)
plus three special characters: dollar sign ($), period (.), and space. Table 7-1 contains the
numeric equivalents of all Radix-50 characters.

Table 7-1:

Numeric Equivalents of Radix-50 Characters

Radix-50
Character

Numeric
Equivalent

Radix-50
Character

Numeric
Equivalent

Space

Unused

7-4 Performing Calculations in ODT

Table 7-1 (Cont.):

Numeric Equivalents of Radix-50 Characters

Radix-50
Character
p

Numeric
Equivalent

Radix-50
Character

Numeric
Equivalent

The following example shows how the asterisk (*) is used in conjunction with the Radix-50
operator (see Section 4.11.2):
_1054/003151 YeAAA 1*3*5=003275 3275

ffiITl

%ACE

Performing Calculations in ODT 7-5

Chapter 8
Additional Debugging Aids
The Task Builder (TKB) on your system allows you to specify the debugger of your choice to
help you in program development. You should build only one debugger into your task at a
time. If you want to switch from one debugger to another, you should rebuild your task.
Section 8.1 shows how you specify other debuggers to TKB for the three environments described
in Section 1.2. Section 8.2 describes the Trace program, a debugging aid available on your
system.

8. 1 Accessing Other Debugging Aids
The following sections show how to specify a debugger other than ODT to be linked with your
object module or modules. The example in each section shows a command line for linking the
Trace debugging aid, as described in Section 8.2. You can specify the file name of any debugger
in place of [l,l]TRACE.OBJ.

8.1.1 MCR Command Line
To link a debugger with your task using MCR, specify the name of the debugger object module
as input to TKB. Follow the debugger object module name with the IDA switch, as shown in
the following example:
TKB>MYTASK=MYFILE, [1 , 1] TRACE/DA

mill

The IDA switch identifies the file specified as a debugger. Because TKB assumes that the file
type of input files is OBJ, you need not specify the file type of the debugger object module.

8.1.2 DCl Command Line
To link a debugger into your task using DCL, specify the name of the debugger object module
as an argument to the IDE BUG qualifier with the LINK command, as shown in the following
example:
$ LINK/DEBUG: [1 , 1]TRACE/TASK : MYTASK MYFILE

mill

Because DCL assumes that the file type of input files for the task builder is OBJ, you need not
specify the file type of the debugger object module.

Additional Debugging Aids 8-1

8.2 The Trace Debugging Program
The Trace program is a debugging aid that can be used instead of or along with ODT to provide
information about the execution of a user task. Trace is most appropriate for use with relatively
simple tasks or with sections of tasks.
Trace is an object module that you specify to TKB when you build your task, as described in
Section 8.1. It is located in the DEBUG.OLB library in directory [1,1] on the system disk, with
the name TRACE .OB]. To extract TRACE.OB] from the library DEBUG.OLB, first set your default
directory and protection User Indentification Code (VIC) to [1,1] on the system disk. Then,
if your command line interpreter (CLI) is MCR, issue the following Librarian Utility Program
(LBR) command:
>LBR TRACE . OBJ=DEBUG . OLB/EX : TRACE @IT]

If your CLI is DCL, issue the following LIBRARY command:
$ LIBRARY/EXTRACT/OUTPUT :TRACE . OBJ DEBUG .OLB TRACE @IT]

Trace is not an interactive program like ODT. When you run your task, Trace is executed once
and prints its listing on pseudo device CL. To run Trace again, you must run your task again.

8.2.1 The Trace Listing
A Trace listing contains two lines of information for each instruction executed in the user's task.
The first line is made up of five octal words, which represents the contents of the following
registers:
•

Current relative program counter (PC)

•

Current PC

•

Next PC

•

Processor Status Word (PSW)

•

Directive Status Word (DSW)

The relative PC is determined by subtracting a user-specified bias value from the actual Pc.
Section 8.2.2 describes how you specify this bias value.
The second line of the Trace listing contains eight octal words representing the contents of the
following:
1- 610

RO to RS

710

Stack pointer

810

The top word of the stack

Example 8-1 is a sample Trace listing for part of a user task.

8-2

Additional Debugging Aids

Example 8-1:
001714
002637

Sample Trace Output

003174
000120

000001
000000

000000

001256

003074

001716 003176 003202 170024 000001
002637 000120 000000 140200 000000

000000

001256

003074

001722 003202 003074 170024 000001
002637 000120 000000 140200 000000

000000

001260

001614 003074 003100 170020 000001
002612 000120 000000 140200 000000

000000

001260

003176
000000

170020
140200

8.2.2 Bias Values and Ranges
You can use the GBLPAT TKB option to specify the following:
•

The bias value to be used in determining the relative PC

•

The range or ranges of task locations to be traced

8.2.2.1 Specifying a Bias Value
To specify a bias value for relative PC calculation, enter an option line in the format shown
next in response to the TKB prompt.
Format

GBLPAT=segname:.BIAS:value
Parameters
segname

Specifies the name of the task's root segment.
value

Specifies the octal value to be subtracted from the actual PC to establish relative Pc. (If a
value is not specified, the initial stack pointer is used.)

8.2.2.2 Specifying Ranges to be Traced
To specify up to four ranges of locations for which execution should be traced, enter an option
line in the format shown next in response to the TKB prompt.
Format

GBLPAT=segname:.RANGE:lowl:highl [ ... :lown:highn]

Additional Debugging Aids 8-3

Parameters
segname

Specifies the name of the task's root segment.
lowl ... lown

Specifies the low addresses, relative to the bias value, of ranges to be traced.
high 1 ... highn

Specifies the high addresses, relative to the bias value, of ranges to be traced.
There can be up to four ranges. You must specify both the low and the high address of each
range.

8-4 Additional Debugging Aids

Appendix A
Error Detection
The On-Line Debugging Tool (OOT) responds to errors in user input and to certain hardwaredetected errors that occur during task execution. This appendix describes these errors, aOT's
response to them, and what action the user can take to correct them.

A. 1 Input Errors
aOT uses the question mark (?) to indicate that it has detected an error in user input. After
displaying the question mark, the debugger generates a carriage return, a line feed, and prompts
for another command.
aOT responds with the question mark to any of the following input errors:
•

Reference to an address without an operator

•

Reference to an address outside the task's partition

•

Reference to a nonexistent register-for example, $20

•

Reference to supervisor space by a non privileged user

•

Input of an illegal character-for example, 8 or 9

If you have typed an incorrect input string-for example, contradictory arguments for the W
command-you may find that the simplest course of action is to cancel the input string by
typing an illegal character. You cannot, however, erase a string once you have entered the
command-the character W, in this case.

aOT does not tell you what error has caused it to display the question mark. However, an
error sometimes causes it to return one of the error codes listed in Section A.2, plus information
on the location at which the error occurred.
In some cases (for example, if you attempt a memory operation when $L is greater than $H),
aOT repeats its prompt but does not display a question mark.

Error Detection A-I

A.2 Task Image Error Codes
As described in Table 5-2, eight Synchronous System Trap (SST) vector registers are used to
contain pointers to error-handling routines. Upon detecting an error condition, ODT activates
the appropriate routine and displays an error message. This message has the form cc:k, where
cc is a 2-character error code and k is the location at which the error occurred. ODT displays
the location as a relative address if there is a relocation register containing a base address less
than the absolute address of the location.
The following examples are error messages from a debugging session:
MP:007414
OD:1,003507

The remainder of this appendix is an alphabetical list of error codes. Each error code is followed
by an explanation and a description of what action the user should take in response to the
error.
BE

Explanation: Breakpoint instruction executed at unexpected location. The address of
the breakpoint instruction does not match the contents of any register, $OB to $7B.
User Action: Examine your code to determine why the unexpected breakpoint occurred;
then continue with the P command.

Explanation: Invalid EMT instruction executed. Only EMT 377 and EMT 376 (for
a privileged task) are allowed by the Executive for execution of Executive directives.
Normally, vector address 30 is used for this trap sequence.
User Action: If you want to use an EMT trap handler that you have written, set SST
vector register 5 ($5V) to the appropriate vector address.

Explanation: Floating-point instruction error. One of the following has occurred:
division by zero; illegal Floating Op Code; flotation overflow or underflow; or conversion
failure.
User Action: Check your code for sequences that may have caused one of these
conditions.

Explanation: Reserved or illegal instruction executed. The task tried to execute a
nonexistent instruction, an Extended Instruction Set (EIS), or Floating Point Processor
(FPP) instruction in a system with no EIS or FPP hardware.
User Action: Check your code for typographical errors or the use of a nonexistent
instruction.

Explanation: lOT instruction executed. Normally, vector address 20 is used for this
trap sequence.
User Action: To change the handling of I/O traps, set SST vector register 3 ($3V) to
the appropriate vector address.

Explanation: Memory-protection violation or illegal memory reference. The task tried
to access a location outside of the ranges mapped or a location which it did not have
the privilege to access.
User Action: Check your code for typographical or programming errors that could lead
to this condition.

A-2 Error Detection

Explanation: Odd address reference on word instruction. The program counter (PC)
contained an odd address when trying to access a word in memory. Also, on some
processors, execution of an illegal instruction.
User Action: Check your code for the use of a word instruction when a byte instruction
was intended (MOV instead of MOVB, for example) or a typographical error in the
address specification.

Explanation: T-bit (trace bit) exception. The T-bit was set by some other mechanism
than a breakpoint or an S or P command. This can occur if bit 4 is set in a word that
is interpreted as the Processor Status Word (PSW) due to its position on the stack.
User Action: Check that the stack contains appropriate values.

Explanation: TRAP instruction executed. Normally, vector address 34 is used for this
trap sequence.
User Action: To change the handling of TRAP instructions, set SST vector register 6
($6V) to the appropriate vector address.

Error Detection A-3

Appendix B
Processor Status Word
The Processor Status Word (PSW), 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 that, when set, causes a trap upon completion of the current instruction

•

Condition codes describing the results of the last instruction executed

The format of the PSW is shown in Figure B-1.
Figure 8-1:
15

14 13

Format of the Processor Status Word
12 11

~--

CARRY
' - - - - OVERFLOW
' - - - - - - ZERO
' - - - - - - - - NEGATIVE
' - - - - - - - - - - TRACE TRAP
L -_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ GEN REG SET

L -_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

PREVIOUS MODE
CURRENT MODE
ZK-491-81

Bits 15 and 14 indicate the current processor mode: user mode (II), supervisor mode (01), or
kernel mode (00). Bits 13 and 12 indicate the previous mode, that is, the mode the machine
was in (user, supervisor, or kernel) prior to the last interrupt or trap.

Processor Status Word 8-1

Bits 7 to 5 show the current priority of the central processor. The central processor operates
at anyone of eight levels of priority (0 to 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 T-bit (trace 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
PSW will be loaded. The T-bit is especially useful in debugging programs, because it provides
an efficient means for stepping through the task one instruction at a time. ODT uses the T-bit
to execute instructions when you are stepping through your program with the S command, as
described in Section 3.5.
The condition codes N, 2, V, and C (bits 3 to 0, respectively) indicate the result of the last
central processor operation. These bits are set as follows:
N=1

If the result was negative

2=1

If the result was zero

V=1

If the operation resulted in an arithmetic overflow

C=1

If the operation resulted in a carry from the most significant bit

B-2 Processor Status Word

Index
A
ABORT command, 1-6
Absolute location, 2-5, 4-4
Absolute address, 2-2
Address
absolute, 2-2, 5-5
relative, 2-2
format, 2-2
relocatable, 2-2, 5-5
calculating, 2-8, 7-1
Address expression
See Expression
American Standard Code for Information
Interchange
See ASCII
Apostrophe operator (')
See Operator
A register, 2-6, 5-3, 6-2
Argument
register, 2-6, 5-3, 6-2
separator, 2-4
Arithmetic calculations, 7-1
Arithmetic operator
See Operator
ASCII
displaying, 4-6
operator, 2-6
byte mode, 4-6
word mode, 4-6
Asterisk separator ( * )
See Separator
At sign command (@), 2-5,4-4
a variable, 2-1

B
Backslash operator (\)
See Operator
B command, 2-7, 3-1,3-2
Bias value, 2-3
Trace program, 8-3
Branch
location, 2-5
offset, 4-5, 7-2
calculating, 4-5
Breakpoint, 3-1, 3-3
address register, 2-6, 3-2, 5-4
clearing, 3-2
instruction register, 2-6, 5-4
proceed count, 3-4
register, 2-6, 5-4
removing, 2-7, 3-2
setting, 2-7,3-1
B register, 2-6, 5-4
Byte location
displaying, 4-2, 4-4
opening, 4-2, 4-4
Byte mode
changing to word mode, 4-3
operator
ASCII, 2-6
octal, 2-7, 4-2

c
Circumflex command r), 2-5, 4-3, 4-4
Command
at sign (@), 2-5, 4-4
B,2-7
circumflex C), 2-5, 4-3, 4-4
D, 2-7
E, 2-7, 6-2

Index-l

Command (cont'd.)
equal sign (=), 2-7, 7-2
F, 2-8, 6-4
G,2-8
I, 2-8
K, 2-8
L, 2-8, 6-4
left angle bracket ( <), 2-5, 4-6
LINE FEED, 2-5, 4-4
N, 2-9, 6-2
0, 2-9, 7-2
P,2-9
R, 2-9
RETURN, 2-4, 4-2
right angle bracket (> ), 2-5, 4-5
S, 2-9
U,2-9
underscore (_), 2-5,4-5
Y. 2-9
variable
a, 2-1
k, 2-1
m,2-1
n, 2-1
x, 2-1
W, 2-10,6-2
X, 1-5, 2-10
Z, 2-10
Comma separator (, )
See Separator
Constant register
See C register
C register, 2-6, 5-3
indicator, 2-7, 7-3
CTRLjC
ODT, 1-6
CTRL/J, 4-4
CTRLjU
ODT,2-7
Current location indicator (.), 7-3

D
Data space, 7-2
command, 2-7
enabling, 1-3
DCL command
linking
ODT, 1-3
ODTID, 1-3
explicitly, 1-4
supervisor-mode libraries, 1-4

Index-2

D command, 2-7
DEBUG command
RSX-llM-PLUS and Micro/RSX, 1-6
Device control
LUN register, 2-6, 5-4, 6-2
Directive Status Word
See DSW
Dollar sign ($),2-5,5-1
Dot (.) indicator
See Register indicator
D register, 2-6, 5-4, 6-2
D-space
See Data space
DSW
register, 2-6, 5-3

E
E command, 2-7, 6-2, 6-3
Equal sign command (=), 2-7
Equal sign operator (=)
See Operator
E register, 2-6, 5-4
Error
detection, A-I
error codes, A-2
task image, A-2
Exit command, 2-10
Expression, 2-3
address, 2-2
evaluating, 2-3, 7-2
format, 2-3
illegal, 2-7
Radix-50
evaluating, 7-4
register address, 2-5

F
F command, 2-8, 6-4
Fill command
See F command
Format
memory listing, 6-5
PSW, B-1
Trace program listing, 8-2
Format register
See F register
F register, 2-6, 5-3

G
GBLPAT
See TKB
G command, 2-8, 3-3, 3-4
General register, 5-1
contents, 5-2
examining, 5-1
setting, 5-1
Go command
See G command
G register, 2-6, 5-4

H
High memory limit register
See H register
H register, 2-6, 5-3, 6-2

I command, 2-8
Indicator
See Register indicator
Instruction space, 3-2, 7-2
command, 2-8
enabling, 1-3
Internal register, 5-2
accessing, 5-2
I register, 2-6, 5-4
I-space
See Instruction space

K
K command, 2-8, 7-1
k variable, 2-1

L
L command, 2-8,6-4
Left angle bracket command ( <), 2-5, 4-6
Limit register
high memory, 5-3, 6-2
low memory, 5-3, 6-2
LINE FEED command, 2-5, 4-4
LINK command, 1-3
/OEBUG qualifier, 8-1
specifying a debugger, 8-1
List command
See L command
Location
absolute, 2-5, 4-4
altering, 4-1

Location (cont' d.)
branch, 4-5
closing, 4-2
displaying, 4-1
format, 4-1
indicator, 7-3
opening, 4-1
ASCII,4-6
branch offset, 4-5
byte, -t-2
next sequential, 4-4
preceding, 4-4
Radix-50, 4-7
word, 4-2
PC-relative, 4-5
reopening last opened, 4-3
returning from, 4-6
Location indicator
See Register indicator
Logical Unit Numbers
See LUN
Loop, 3-4
Low limit register
See L register
L register, 2-6, 5-3, 6-2
LUN
OOT
assigning, 1-4

M
Mask register
See M register
MCR command
linking
00T,l-2
00TID,l-3
explicitly, 1-4
supervisor-mode libraries, 1-4
Memory
E command, 6-2
F command, 6-4
fill command, 2-8
H register, 2-6
L command, 6-4
limit register
high, 5-3, 6-2
low, 5-3, 6-2
list command, 2-8
listing
format, 6-5
L register, 2-6

Index-3

Memory (cont'd.)
N command, 6-2
search command, 2-7,2-9,2-10,6-2
W command, 6-2
Message
invocation, 1-5
Minus sign operator ( -)
See Operator
M register, 2-6, 5-3, 6-2
m variable, 2-1

N
N command, 2-9,6-2, 6-3
n variable, 2-1

o
o command, 2-9, 7-2
Octal operator, 2-3, 2-7
ODT
assigning device LUN, 1-4
exiting, 1-5
invoking, 1-5
linking, 1-2
overview, 1-1
redirecting output, 1-4
ODTID module, 1-3
Offset, 2-3
branch, 7-2
calcula ting, 2 -9, 7-2
instruction and data space, 7-2
negative, 7-2
PC-relative, 7-2
positive, 7-2
Operating system
return to, 2-10
Operator, 2-3, 2-4
apostrophe ('), 2-6, 4-6
arithmetic, 2-3
ASCII
byte mode, 4-6
word mode, 4-6
backslash (\), 2-7,4-2,4-3
byte mode
ASCII,2-6
octaL 2-7, 4-2
equal sign (=), 7-2
minus sign ( -), 2-3, 2-4
percent sign (%), 2-7, 4-7
plus sign ( +), 2-3, 2-4
quotation mark (1/), 2-6, 4-6

Index-4

Radix-50
word mode, 4-7
slash (j), 2-7, 4-2, 4-3
word mode
ASCII, 2-6
octal, 2-7, 4-2
Radix-50, 2-7

p
P command, 2-9, 3-3, 3-4
PC-relative
location, 2-5, 4-5
offset, 2-9, 7-2
Percent sign operator ( %)
See Operator
Plus sign operator ( + )
See Operator
Proceed command
See P command
Proceed count, 3-4
register, 5-4
Processor Status Word
See PSW
Program counter
See PC-relative
Prompt
ODT, 1-5
PSW, B-1
format, B-1
register, 2-6, 5-3

Q
Q register, 2-6,5-3, 7-2
indicator, 2-9, 7-3
Quantity register
See Q register
Question mark (?)
user input error, A-I
Quotation mark operator (1/)
See Operator

R
Radix-50
character set, 7-4
displaying, 4-7
evaluating, 7-4
numeric equivalents, 7-4
opening, 4-7

operator
word mode, 2-7,4-7
separator (*), 2-4, 7-4
Range
Trace program, 8-3
R command, 2-9
Reentry vector register
See X register
Reference
search, 6-3
Register, 2-5,5-1
A, 2-6, 5-3, 6-2
address expression, 5-1
B, 2-6,5-4
clearing, 3-2
breakpoint
address, 5-4
instruction, 5-4
proceed count, 5-4
C, 2-6,5-3
D, 2-6, 5-4, 6-2
E, 2-6,5-4
F, 2-6,4-1,5-3
G, 2-6,5-4
general, 5-1
contents, 5-2
examining, 5-1
setting, 5-1
H, 2-6, 5-3, 6-2
I, 2-6,5-4
indicator, 2-7, 2-9
internal, 5-2
accessing, 5-2
L, 2-6, 5-3, 6-2
M, 2-6, 5-3, 6-2
memory operations, 6-1
Q, 2-6, 5-3, 7-2
R, 2-6, 5-4, 5-5
clearing, 5-6
setting, 2-9, 5-6
S, 2-6,5-3
search limit, 6-2
V, 2-6,5-4
W, 2-6,5-3
X, 2-6, 5-3, 5-6
Register indicator, 2-3
C register, 2-3, 7-3
current location (.), 2-3, 7-3
Q register, 2-3, 7-3
Register set, 5-3

Relative
address, 2-2
format, 2-2
branch location, 2-5, 4-5
Relocatable
address, 2-2, 5-5
calculating, 2-8, 7-1
Relocation register
See R register
RETURN command, 2-4,4-2
Right angle bracket command (> ), 2-5, 4-5
R register, 2-6, 5-4, 5-5
clearing, 5-6
setting, 2-9, 5-6

s
S command, 2-9,3-4
Search
argument register, 2-6, 5-3, 6-2
byte, 6-3
command, 6-2
E, 6-3
N,6-3
W,6-3
limit register, 6-2
mask register, 2-6, 5-3, 6-2
memory
command, 2-7, 2-9
reference, 6-3
word,6-3
Semicolon separator (;)
See Separator
Separator
argument (,), 2-4
argument (;), 2-4
Radix-50 (*), 2-4, 7-4
Slash operator (j)
See Operator
S register, 2-6, 5-3
SST
stack contents register, 2-6, 5-4
vector
handling, 2-9
register, 2-6, 5-4
Step command
See S command
Supervisor mode, 1-4, 3-2
Supervisor-mode library, 1-4
command, 2-10
debugging, 1-4
installing READ/WRITE access, 1-4

Index-5

Supervisor-mode library (cont'd.)
setting, 2-10
Synchronous System Trap
See SST

T
Task
fixed, 5-6
Task Builder
See TKB
Task execution
aborting, 1-6
beginning, 2-8, 3-3
continuing, 2-9, 3-3
resuming, 1-6, 3-4
Task map, 1-2, 1-3,5-5
TE trap, 1-6
TKB
IDA switch, 8-1
GBLPAT option, 8-3
linking
ODT, 1-2
ODTID, 1-3
supervisor-mode libraries, 1-4
specifying a debugger, 8-1
Trace program, 8-2
listing, 8-2
format, 8-2
Trap, 5-5, A-2
handling, 2-9,5-5
SST vector register, 5-5
TE, 1-6

u
U command, 2-9
Underscore command (_), 2-5,4-5
User mode, 3-2
command, 2-9
setting, 2-9

v
Variable, 2-1
V command, 2-9
Vector
reentry register, 5-3, 5-6
SST register, 2-9
V register, 2-6, 5-4

W
W command, 2-10, 6-2, 6-3

Index-6

Word location
displaying, 4-2, 4-4
opening, 4-2, 4-4
underscore command (_), 4-5
Word mode
changing to byte mode, 4-3
operator
ASCII,2-6
octal, 2-7, 4-2
Radix-50, 2-7
W register, 2-6, 5-3

X
X command, 1-5, 2-10
X register, 2-6, 5-3, 5-6
x variable, 2-1

z
Z command, 2-10

RSX-llM-PLUS and Micro/RSX
Debugging Reference
Manual
AA-JS09A-TC

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RSX-llM-PLUS and Micro/RSX
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AA-JS09A-TC

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