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22
BIOS POST Checkpoint Codes
The POST code checkpoints are references and instructions used
during the BIOS pre-boot process. The following table describes
the checkpoints and associated beep codes, if any, that may
occur during the POST portion of the BIOS
Checkpoint
Beep Code
Code
01h
One short
beep before
boot
02h
03h
04h
06h
07h
08h
Description
Verify Real Mode. If the CPU is in protected
mode, turn on A20 and pulse the reset line,
forcing a shutdown 0.
NOTE: Hook routine should not alter DX,
which holds the powerup CPUID.
Disabel Non-Maskable Interrupts (NMI).
Get CPU type from CPU registers and other
methods.
Save CPU type in NVRAM.
NOTE: Hook routine should not alter DX,
which holds the powerup CPUID.
Initialize system hardware. Reset the DMA
controllers, disable video, clear any pending
interrupts from the real-time clock and
setup port B register.
Disable system ROM shadow and start to
execute ROMEXEC code from the flash part.
This task is pulled into the build only when
the ROMEXEC relocation is installed.
Initialize chipset registers to the Initial POST
Values.
3 Getting Started
.
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