PDP-9 Basic Exerciser

The PDP-9 Basic Exerciser is a diagnostic program designed to test the Central Processor (CP), core memory, and associated I/O devices of a basic PDP-9 configuration. It performs comprehensive tests on all operate group and memory reference instructions, the adder (including bit-by-bit and random pair tests), memory checkerboard patterns, the real-time clock, punch, reader, Teletype (TTY), and program interrupt functions.

The program runs continuously, with I/O operations (punch, read, print) interrupting at device rates and the real-time clock generating random interrupts (between 2 and 9 seconds). Operators can modify program execution using nine "ACS functions" (console switches) to inhibit specific tests, loop on particular diagnostic routines (like adder or memory checkerboard tests), or control program relocation between 4K memory fields. It requires all 8K of core memory and can relocate itself to optimize testing.

Error conditions trigger specific halts (tagged "EXXX") with debugging information, and recovery often involves pressing the CONTINUE button. The program provides operational feedback through the TTY, printing "COMPLETE" after a set number of successful passes and issuing "R NO TAPE" or "P NO TAPE" messages if I/O media are absent. A common interrupt service routine handles all device and clock interrupts, preserving system state and resuming the interrupted test. Prior to running this exerciser, all other relevant MAINDEC diagnostics for the PDP-9 should be executed.