F36P Macro Internal Operations Manual Jul62

This document is the "Internal Operations Manual" for the MACRO FIO-DEC assembly program, developed by Digital Equipment Corporation (DEC) for the PDP-1 computer.

Key aspects of the document and the assembler:

1. Origin and Purpose: MACRO FIO-DEC is an adaptation of the MACRO III assembler from MIT's TX-0, tailored for the PDP-1 due to their similar logical designs. This manual provides an in-depth, internal description of its workings, intended for internal use and potential improvements.
2. Two-Pass Assembler: The program operates in two passes, employing a macro-instruction facility that generates code from stored model statements.
3. Character-Based Processing: It functions primarily as a linear scan character processor, examining each character sequentially in each pass.
4. I/O and Error Handling: The system uses buffered input/output to reduce wear on equipment and includes optional parity checking for tape reads. It also details an error alarm routine for diagnostics.
5. Core Components Detailed: The manual outlines the internal logic and data structures for various functions:
   • Input Tape Handler: Managing character input, buffering, and parity checks.
   • Initialization and Reset: Sequences for starting and resetting the assembly process.
   • Symbol Generator and Processor: Handling integers, pseudo-instructions, and multi-character symbols, including their definition, evaluation, and storage using a sorted symbol table with a logarithmic search.
   • Storage and Location Assignments: Managing memory, location counter updates, and symbol definitions (variables and constants).
   • Macro-Instruction Facility: Extensive coverage of macro tables, definitions, and usage, including the complexities of nested macro calls and dummy symbol management.
   • Symbol Package: Routines for printing symbol and macro definitions after assembly.
6. Technical Focus: The document is highly technical, detailing specific routines and indicators (e.g., rch for characters, mii for macro instruction indicator, wrd for accumulated word value) and discussing data structures like the symbol table, macro table (mai), and dummy symbol tables (dsm, dss, dsv).
7. Development Context: As a "Preliminary Draft Description," it provides foundational knowledge for internal programmers, acknowledging that the program, while functional and stable, may not be "ideal or perfect" and encourages compatibility in any proposed changes.