3-1
CHAPTER
3
Power-On Self-Test
This chapter describes how to initiate power-on self-test (POST) diagnostics. POST is
a firmware program that can help determine if a portion of the system has failed.
POST verifies the core functionality of the system, including operation the CPU,
motherboard, memory, and some on-board I/O devices. POST can be run even if the
system is unable to boot.
This chapter contains the following topics:
■ Section 3.1, “POST Overview” on page 3-1
■ Section 3.2, “How to Use POST” on page 3-2
■ Section 3.3, “Pre-POST Preparation” on page 3-2
■ Section 3.4, “Viewing the POST Menus” on page 3-5
■ Section 3.5, “Initializing POST” on page 3-5
■ Section 3.6, “Maximum and Minimum POST Levels” on page 3-6
■ Section 3.7, “POST Progress and Error Reporting” on page 3-25
■ Section 3.8, “Bypassing POST” on page 3-27
■ Section 3.9, “Resetting Variables to Default Settings” on page 3-27
■ Section 3.10, “Viewing the Default NVRAM Settings” on page 3-28
■ Section 3.11, “Initializing Motherboard POST” on page 3-28
3.1 POST Overview
POST detects most system faults and is located in the system board OpenBoot™
PROM. POST can be invoked at power up by the OpenBoot program, depending on
the setting of two environment variables, the diag-switch? and the diag-level
flag. The diag-switch? and the diag-level flag are stored in nonvolatile RAM
(NVRAM).
POST diagnostic and error message reports are displayed on a console terminal.
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