PMAX Boot ROM

This document details the PMAX Boot ROM, covering how to access it, its commands, Power On Self Test (POST) diagnostics, and security considerations.

Key Points:

1. Accessing the Boot Prompt: Users can access the boot prompt by pressing Control-C during the OS load process or by halting the operating system.
2. Boot ROM Commands: A list of commands is provided, including:
   • auto: Starts the automatic boot process.
   • boot: Used to manually boot a file or OS image, with options for single-user mode or specific devices.
   • setenv: Configures NVRAM variables (e.g., bootmode a for autoboot, bootdev to set default boot device and kernel).
   • printenv: Displays current NVRAM contents.
   • test -c: Shows system statistics and connected SCSI devices.
   • dump, e, fill: Commands for memory and register manipulation.
   • help / ?: Provides command assistance.
3. OS Booting:
   • The NVRAM is typically configured for automatic OS boot.
   • Specific instructions are given for booting NetBSD 1.6.2 from CD-ROM, noting the need for installboot(8) to modify the ISO image and specifying compatible CD-ROM drives.
4. Power On Self Test (POST):
   • The POST displays numeric sequences during startup; "FAILURE" or "??" indicate a subsystem problem.
   • A detailed table maps Console Codes and Rear LED POST codes to specific hardware failures (e.g., Video SIMM, SCSI, Serial chip, System module, Keyboard/Mouse, Ethernet, Memory, CPU). These codes are crucial for diagnosing hardware issues.
5. Security and OS Specifics:
   • No Firmware Boot Password: PMAX firmware (pre-7.02 F/W) lacks a boot password, making physical console security critical.
   • Ultrix 4.4: Boots to a limited 'bin' single-user mode, requiring the root password for full access.
   • NetBSD 1.6.2: Also provides no console security for pmax due to its firmware bootloader and the lack of a firmware password, allowing trivial root access from the console.