Sun Microsystems Ultra 5, Service Manual

Page: 49 / 258

3-1
C H A P T E R
3
Power-On Self-Test
This chapter describes how to initiate power-on self-test (POST) diagnostics.
This chapter contains the following topics:
■
Section 3.1 “POST Overview” on page 3-1
■
Section 3.2 “Pre-POST Preparation” on page 3-2
■
Section 3.3 “Initializing POST” on page 3-5
■
Section 3.4 “Maximum and Minimum POST Levels” on page 3-7
■
Section 3.5 “Bypassing POST” on page 3-22
■
Section 3.6 “Resetting Variables to Default Settings” on page 3-22
■
Section 3.7 “Initializing Motherboard POST” on page 3-23
3.1 POST Overview
POST is useful in determining if a portion of the system has failed and should be
replaced. POST detects approximately 95 percent of system faults and is located in
the motherboard OpenBoot™ PROM (OBP). The setting of two NVRAM variables,
diag-switch?
and
diag-level
, determines whether POST is executed and to
what level (see Section 3.3 “Initializing POST” on page 3-5).