ddtSource

This document, dated August 20, 1966, is an assembly language listing for a program identified as "DDT" (Dynamic Debugging Technique), likely for an early computer system such as the PDP-1.

The document details the debugger's structure and functionality, including:

• Instruction Set Definitions: A comprehensive list of symbolic "flex" instructions (e.g., flex and, flex jmp, flex lac) mapped to their corresponding octal machine codes.
• Macros and Subroutines: Definitions of higher-level operations (e.g., initialize, index, listen, load, clear) built from the basic instruction set to perform common programming tasks.

• Extensive Debugging and Utility Routines: Numerous named routines cover a wide range of functions, including:

  • Input parsing and command handling (uc, lc, sqo, quo).
  • Symbol table management (reading, permuting, deleting symbols, lookups - tbl, pev, tys).
  • Address resolution and searching (eas, wds, pad).
  • Data and instruction printing (octal, decimal, BCD, instruction mnemonics, addresses, symbols - pi, pbx, opt).
  • Input/Output operations, particularly for paper tape (punching various block formats, titles, reading blocks - pun, pbb, rbk, ttl).
  • System state manipulation (setting break addresses, handling traps, zeroing registers - bk, tr, zro).
  • Case shift filtering and error handling.

• Dispatch Tables: Centralized tables (e.g., dtb, ftp) that manage command routing and output formatting based on input.

• Constants and Variables: Definitions of system parameters, character codes, data buffers, and memory locations used by the debugger.

In essence, the document provides the low-level implementation of a sophisticated debugger, outlining its capabilities to interpret commands, manage symbols, inspect memory, control program flow, and handle various forms of data input and output.