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POST code checkpoints
The following table shows the checkpoints, LED codes, and task description of events that
may occur during the POST portion of the BIOS:
Check
point
Diagnostic LED decoder
G=Green, R=Red, O=Orange
Description
03 Off Off G G Disable NMI, Parity, video for EGA, and DMA controllers. Initialize
BIOS, POST, Runtime data area. Also initialize BIOS modules
on POST entry and GPNV area. Initialized CMOS as mentioned
in the Kernel Variable “wCMOSFlags.”
04 Off G Off Off Check CMOS diagnostic byte to determine if battery power is OK
and CMOS checksum is OK. Verify CMOS checksum manually
by reading storage area. If the CMOS checksum is bad, update
CMOS with power-on default values and clear passwords.
Initialize status register A.
Initialize data variables that are based on CMOS setup
questions. Initializes both the 8259 compatible PICs in the
system.
05 Off G Off G Initialize the interrupt controller in hardware (generally PIC) and
interrupt vector table.
06 Off G G Off Do R/W test to CH-2 count reg. Initialize CH-0 as system timer.
Install the POSTINT1Ch handler. Enable IRQ-0 in PIC for system
timer interrupt.
Traps INT1Ch vector to “POSTINT1ChHandlerBlock.”
08 G Off Off Off Initialize the CPU. The BAT test is being done on KBC. Program
the keyboard controller command byte is being done after Auto
detection of KB/MS using AMI KB-5.
C0 R R Off Off Early CPU Init Start — Disable Cache - Init Local APIC
C1 R R Off G Set up boot strap processor information.
C2 R R G Off Set up boot strap processor for POST.
C5 R O Off G Enumerate and set up application processors.
C6 R O G Off Re-enable cache for boot strap processor.
C7 ROGGEarly CPU Init Exit.
0A G Off G Off Initialize the 8042 compatible keyboard controller.
0B G Off G G Detect the presence of PS/2 mouse.
0C G G Off Off Detect the presence of keyboard in KBC port.