What Are Post Diagnostics For - Sun Microsystems Sun Fire V480 Administration Manual

When system power is turned on, the OpenBoot firmware begins running directly
out of the Boot PROM, since at this stage system memory has not been verified to
work properly.
Soon after power is turned on, the Boot Bus controller and other system hardware
determine that at least one CPU module is powered on, and is submitting a bus
access request, which indicates that the CPU in question is at least partly functional.
This becomes the master CPU, and is responsible for executing OpenBoot firmware
instructions.
The OpenBoot firmware's first actions are to probe the system, initialize the data
switches, and figure out at what clock speed the CPUs are intended to run. After
this, OpenBoot firmware checks whether or not to run the power-on self-test (POST)
diagnostics and other tests.
The POST diagnostics constitute a separate chunk of code stored in a different area
of the Boot PROM (see ).
FIGURE 6-2
POST
Boot
IDPROM
8 Kbytes 2 Mbytes
PROM
OpenBoot
firmware
Boot PROM and IDPROM
FIGURE 6-2
The extent of these power-on self-tests, and whether they are performed at all, is
controlled by configuration variables stored in a separate firmware memory device
called the IDPROM. These OpenBoot configuration variables are discussed in
"Controlling POST Diagnostics" on page 88.
As soon as POST diagnostics can verify that some subset of system memory is
functional, tests are loaded into system memory.

What Are POST Diagnostics For?

The POST diagnostics verify the core functionality of the system. A successful
execution of the POST diagnostics does not ensure that there is nothing wrong with
the server, but it does ensure that the server can proceed to the next stage of the boot
process.
Chapter 6 Diagnostic Tools 85