PDP-1 DDT Listing Feb63

This document is an assembly language listing for a debugger program named "ddt" (likely "Dynamic Debugging Technique"), dated February 8, 1963, potentially authored by A. Kotok.

The listing details a comprehensive set of low-level routines and data definitions for interacting with a computer system and debugging programs. Its key functionalities include:

1. Program Control & Execution: Routines for dispatching commands, setting up and handling traps/breakpoints, executing instructions, and managing program flow (e.g., define, tr, bk, xec).
2. Input/Output Operations: Extensive support for reading data blocks (rbk), punching information to an output device (pun, pbw), and printing instructions, octal/decimal numbers, and symbols to a display (pi, eql, tou, pbx). It also handles various forms of character input (upper/lower case, numbers, letters, symbols, flexo codes).
3. Symbol & Address Management: Functions for defining and manipulating symbols (def, tbl), performing effective address searches (eas), and managing system registers and memory locations.
4. Data Conversion & Formatting: Routines for converting between octal and decimal representations (oct, dec, opt), handling different character encodings (c77 tables), and formatting output (e.g., BCD).
5. Interactive & Utility Features: Includes routines for error handling (err), initializing registers (zro), cursor control (tab, bs), parsing special characters like brackets, and managing various system modes (octal-decimal, symbolic-constant). A central dispatch table (dtb) routes different input types to their respective processing routines.

In essence, it's a foundational debugger implementation, providing the core tools for inspecting, controlling, and modifying a program's execution and data at a low level.