PDP-7 Programming Manual, DDT Debugging System Program Description

This document details the DDT (DEC Debugging Tape) debugging system, designed for the PDP-7 computer and compatible with the PDP-4. Its primary purpose is to significantly reduce the time required for program debugging by providing an interactive environment. Users can control program execution, examine and modify program code or data in real-time, and set breakpoints and traps to efficiently locate and correct errors. DDT allows for immediate patches to be made and output as loadable patch tapes, circumventing the need for full program reassembly after each fix. It maintains a symbol table, which includes standard PDP-7 mnemonics and can be expanded with user-defined symbols, enabling symbolic referencing within programs. The manual covers commands for loading programs, controlling data display modes, program examination and modification, handling special registers, searching memory, and punching corrected program segments. DDT occupies the highest 2000 registers of memory.