POST and OpenBoot work together in the system to test and manage system hardware.
POST resides in the OpenBoot PROM on each CPU/Memory+ board, I/O+ board, and Disk board. When the system is turned on, or if a system reset is issued, POST detects and tests buses, power supplies, boards, CPUs, SIMMs, and many board functions. POST controls the status LEDs on the system front panel and all boards. POST displays diagnostic and error messages on a console terminal, if available.
Only POST can configure the system hardware, and only POST can enable hot-pluggable boards. If a new unit (board or modular power supply) is added to the card cage after the system has booted, the new unit will not work until the system is rebooted, at which time POST reconfigures the system, using the units that are found in the system at that time.
POST does not test drives or internal parts of SBus cards. To test these devices, run OBP diagnostics manually after the system has booted. Refer to the OpenBoot Command Reference manual for instructions.
OpenBoot provides basic environmental monitoring, including detection of overheating conditions and out-of-tolerance voltages. For example, if an overheated board is found, OpenBoot issues a warning message. If the temperature passes the danger level, POST will put the overheated board(s) in low power mode.
OpenBoot also provides a set of commands and diagnostics at the ok prompt. For example, you can use OpenBoot to set NVRAM variables that reserve a board or a set of SIMMs for hot-sparing.
The following OpenBoot commands may be useful for diagnosing problems:
Use the show-devs command to list the devices that are included in the system configuration.
Use the printenv command to display the system configuration variables stored in the system NVRAM. The display includes the current values for these variables, as well as the default values.
If the system cannot communicate with a 10BASE-T network, the Ethernet link test setting for the port may be incompatible with the setting at the network hub. See "Failure of Network Communications" for further details.
The probe-scsi command locates and tests SCSI devices attached to the system. probe-scsi is run from the OpenBoot prompt.
When it is not practical to halt the system, you can use SunVTS as an alternate method of testing the SCSI interfaces.
For more information, refer to:
OpenBoot 3.x Command Reference, part number 802-3242
Writing FCode 3.x Programs, part number 802-3230