44 | Chapter 4: Useful help
Checkpoint Description
40
Detect different devices (Parallel ports, serial ports, and coprocessor in CPU, etc.) successfully installed in the
system and update the BDA, EBDA…etc.
52
Updates CMOS memory size from memory found in memory test. Allocates memory for Extended BIOS
Data Area from base memory. Programming the memory hole or any kind of implementation that needs an
adjustment in system RAM size if needed.
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.
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. Check boot password if installed.
8C
Late POST initialization of chipset registers.
8D
Build ACPI tables (if ACPI is supported).
8E
Program the peripheral parameters. Enable/Disable NMI as selected.
90
Initialization of system management interrupt by invoking all handlers. Please note this checkpoint comes right
after checkpoint 20h.
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. Display boot option popup menu.
A7
Displays the system configuration screen if enabled. Initialize the CPU’s before boot, which includes the
programming of the MTRR’s.
A9
Wait for user input at config display if needed.
AA
Uninstall POST INT1Ch vector and INT09h vector.
AB
Prepare BBS for Int 19 boot. Init MP tables.
AC
End of POST initialization of chipset registers. De-initializes the ADM module.
B1
Save system context for ACPI. Prepare CPU for OS boot including final MTRR values.
00
Passes control to OS Loader (typically INT19h).
