Cpu Identification Program

Summary:

This document provides the source code and documentation for a PDP-8 CPU Identification Program. The purpose of this software is to programmatically identify the specific model of a PDP-8 computer upon which it is running.

Key aspects of the document include:

• Problem Statement: The document highlights the limitations of earlier identification methods (such as those in FOCAL, 1969), which relied on imprecise software timing loops that frequently caused misidentification, especially on newer models like the DECMATE or the PDP-8/I and PDP-8/L.

• Methodology: The program employs a series of non-timing-based tests that exploit specific architectural "quirks" or features unique to various models of the PDP-8 family. These include:

  • Architecture-Specific Instructions: Testing for specific instruction behaviors (e.g., combined rotate operations, byte-swap, or instructions that clear the accumulator differently).
  • Hardware Feature Detection: Checking for the presence or behavior of specific interface registers (e.g., for the LINC-8 or the KK8 series processors).

• Operating Contexts: The program includes comprehensive logic to handle different operating environments, such as running standalone from the front panel, or under an operating system like OS/8 or P?S/8, ensuring that console output is handled correctly without disrupting existing system states or logical console overlays.

• Technical Details: The document includes the assembly listing, definitions for instructions (LINC-8, PDP-12), various string-printing routines, and a final identification routine that returns the identified model as a value in the accumulator.