F36P PDP1 Macro Internals

This internal operations manual describes the MACRO assembly program, specifically the FIO-DEC version for the PDP-1 computer, which is based on the MACRO III assembler for the TX-O. The program is a two-pass assembler featuring a macro-instruction facility. It functions as a linear scan character processor, utilizing buffered input/output and optional parity checks for efficiency and reliability.

The document systematically details the assembler's internal architecture, covering:

1. Input and Initialization: How characters are handled, the program's initialization and reset sequences, and the generation and processing of various symbol types (integers, pseudo-instructions, and user-defined symbols). Symbol processing relies on a sorted symbol table that uses a binary search and a unique "zone bit inversion" method for alphabetical ordering.
2. Storage and Location Management: Explanation of how words are stored, how location assignments are made, and the different ways symbols (variables, address tags, parameters) are defined.
3. Pseudo-instructions: Detailed descriptions of specific pseudo-instructions such as Repeat, Start, Dimension, and Constants, including their operational logic and limitations.
4. Macro Instruction Facility: The core of the program, detailing the list structure used for macro storage, the organization of macro instruction tables (mai), and the encoding of elements like storage words, dummy symbols, and constants. It explains macro definition and usage, noting that while macro calls within macro definitions are permitted, recursive macro definitions are not.
5. Error Handling and Utilities: Mechanisms for detecting and alarming errors, a "start over" sequence, and the "symbol package" which manages and prints symbol tables.

The manual acknowledges that this preliminary draft describes a functional but not "ideal or perfect" program, advising against fundamental changes, particularly those affecting source language compatibility, to ensure continued service on the PDP-1.