Sun Microsystems Netra T4 AC100 Service And System Reference Manual page 61

Flash PROM
The flash PROM is divided into quadrants that are dedicated to Sun Blade 1000 OBP,
Sun Fire E280R OBP/Netra T4 OBP, POST and OBDiag, respectively. A flash update
involves two quadrants, either 0 and 1, or 2 and 3. You can download the quadrants
from a standalone utility, bootable DVD-ROM, or from the network. The updates are
available in binary or UNIX shell formats.
During a flash PROM update, the OBP firmware overwrites the upper half of PROM
(where POST resides), keeping the original OBP unchanged. After the new OBP is
tested successfully, the original OBP is overwritten with the new OBP. Finally, after
the OBP is tested again, POST is reloaded into the upper half of PROM.
OBP Prompt
On dual processor systems, the OBP prompt includes the CPU number:
{0} ok
Resets
When the system is first powered up, the configuration is determined using
information stored in the motherboard and CPU EEPROMS (CPU speed, memory
configuration, and so forth) and is saved in the BootBus Controller (BBC) SRAM.
This is termed a Configuration Reset. Subsequent system power cycles generate a
configuration reset.
A Soft Reset occurs on subsequent system resets, which uses the BBC's SRAM
configuration information. To avoid booting with corrupted configuration
information, a checksum is performed on the data. If the data is found to be corrupt,
the subsequent reset reverts to a configuration reset.
Chapter 4 Troubleshooting 4-9