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Checkpoint Description
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.
50 Programming the memory hole or any kind of implementation that
needs an adjustment in system RAM size if needed.
52 Updates CMOS memory size from memory found in memory test.
Allocates memory for Extended BIOS Data Area from base memory.
60 Initializes NUM-LOCK status and programs the KBD typematic rate.
75 Initialize Int-13 and prepare for IPL detection.
78 Initializes IPL devices controlled by BIOS and option ROMs.
7A Initializes remaining option ROMs.
7C Generate and write contents of ESCD in NVRam.
84 Log errors encountered during POST.
85 Display errors to the user and gets the user response for error.
87 Execute BIOS setup if needed / requested.
8C Late POST initialization of chipset registers.
8E Program the peripheral parameters. Enable/Disable NMI as selected
90 Late POST initialization of system management interrupt.
A0 Check boot password if installed.
A1 Clean-up work needed before booting to OS.
A2 Takes care of runtime image preparation for different BIOS modules.
Fill the free area in F000h segment with 0FFh. Initializes the
Microsoft IRQ Routing Table. Prepares the runtime language module.
Disables the system configuration display if needed.
A4 Initialize runtime language module.
A7 Displays the system configuration screen if enabled. Initialize the
CPU’s before boot, which includes the programming of the MTRR’s.
A8 Prepare CPU for OS boot including final MTRR values.
A9 Wait for user input at config display if needed.
AA Uninstall POST INT1Ch vector and INT09h vector. Deinitializes the
ADM module.
AB Prepare BBS for Int 19 boot.
AC End of POST initialization of chipset registers.
B1 Save system context for ACPI.
00 Passes control to OS Loader (typically INT19h).
79