PDP-X Diagnostic Goals

This document outlines the goals for diagnostic software for the PDP-X system. The primary purpose of these diagnostics is for field maintenance and system acceptance, rather than in-house production which will use specialized equipment. A key premise is that due to a substantial amount of "hard-core" logic and general inaccessibility of much of the PDP-X's logic to the diagnostic processor, detailed, module-level diagnosis will not be possible.

Therefore, the diagnostics will function more like "exercisers" (similar to the PDP-9), designed to detect errors in data paths, noise, and repetition rate problems, as well as validate memories and I/O devices. To ensure the proper operation of basic timing, data paths, and instruction sequencing, the system will provide:

1. Off-line cycling of main memory for basic operation verification and maintenance.
2. Basic control memory loops to test central processor registers and fast memory.
3. Maintenance console features allowing single instruction execution, single memory cycle execution, and control memory single-step.

Diagnostic programs are designed to assume the basic control processor is functioning. Tests for I/O devices will validate both the control operation and the physical data medium. Central processor diagnostics will focus on performing as many "hard computations" as possible, progressing from general instruction validation to detailed data validation. All diagnostics will be modular, limited to 4K in size, to minimize rework for Model I Systems.