Techniques, Cute Ideas, and Programming Tricks for the PDP-11

This document is a 1970 technical memorandum from D. Knight providing a collection of programming tips and tricks for the PDP-11 architecture. The content includes:

• Trap Handling: A technique to load unused trap vectors with a specific routine that halts and allows inspection of the trap source.
• Programming Tricks: Various instruction-level hacks, including register manipulation (adding/subtracting from registers), using condition codes to pass flags, and efficient stack management.
• Equivalences: A comparative table between JMP and MOV instructions and their effects on condition codes.
• Trap Handler: A method to simulate a two-word JSR using a one-word trap instruction to jump to routine tables.
• Recursion: An example illustrating how to perform recursive string scanning to find matching parentheses.
• Pseudo-assembly Options: A method for conditional assembly by exploiting how code is loaded into memory.
• I/O Buffering: An obscure approach to double-buffering using co-routines within the IOX framework.