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Chapter 4 47
POST code checkpoints
The POST code checkpoints are the largest set of checkpoints during the BIOS pre-boot process. The
following table describes the type of checkpoints that may occur during the POST portion of the BIOS:
Checkpoint Description
03 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 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.
Initializes data variables that are based on CMOS setup questions. Initializes both
the 8259 compatible PICs in the system.
05 Initializes the interrupt controlling hardware (generally PIC) and interrupt vector table.
06 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 Initializes 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.
0A Initializes the 8042 compatible Key Board Controller.
0B Detects the presence of PS/2 mouse.
0C Detects the presence of Keyboard in KBC port.
0E Testing and initialization of different Input Devices. Also, update the Kernel Variables.
Traps the INT09h vector, so that the POST INT09h handler gets control for IRQ1.
Uncompress all available language, BIOS logo, and Silent logo modules.
13 Early POST initialization of chipset registers.
24 Uncompress and initialize any platform specific BIOS modules.
30 Initialize System Management Interrupt.
2A Initializes different devices through DIM.
See DIM Code Checkpoints section of document for more information.
2C Initializes different devices. Detects and initializes the video adapter installed in the
system that have optional ROMs.
2E Initializes all the output devices.
31 Allocate memory for ADM module and uncompress it. Give control to ADM module
for initialization. Initialize language and font modules for ADM. Activate ADM
module.
33 Initializes the silent boot module. Set the window for displaying text information.
37 Displaying sign-on message, CPU information, setup key message, and any OEM
specific information.
38 Initializes different devices through DIM. See DIM Code Checkpoints section of
document for more information.
39 Initializes DMAC-1 & DMAC-2.
3A Initialize RTC date/time.
3B Test for total memory installed in the system. Also, Check for DEL or ESC keys to
limit memory test. Display total memory in the system.
3C Mid POST initialization of chipset registers.
40 Detect different devices (Parallel ports, serial ports, and coprocessor in CPU, … etc.)
successfully installed in the system and update the BDA, EBDA…etc.