185BIOS POST Checkpoint CodesThe following table describes the checkpoints and associatedbeep codes, if any, that may occur during the POST portion ofthe BIOS.CheckpointCode Beep Code Description01h One shortbeep beforeboot02h Verify Real Mode. If the CPU is in protectedmode, turn on A20 and pulse the reset line,forcing a shutdown 0.NOTE: Hook routine should not alter DX,which holds the powerup CPUID.03h Disabel Non-Maskable Interrupts (NMI).04h Get CPU type from CPU registers and othermethods.Save CPU type in NVRAM.NOTE: Hook routine should not alter DX,which holds the powerup CPUID.06h Initialize system hardware. Reset the DMAcontrollers, disable video, clear any pendinginterrupts from the real-time clock andsetup port B register.07h Disable system ROM shadow and start toexecute ROMEXEC code from the flash part.This task is pulled into the build only whenthe ROMEXEC relocation is installed.08h Initialize chipset registers to the Initial POSTValues.
