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64 Chapter 4
12h Use walking 1’s algorithm to check out interface in CMOS circuitry. Also set real-
time clock power status, and then check for override.
13h Reserved
14h Program chipset default values into chipset. Chipset default values are
MODBINable by OEM customers.
15h Reserved
16h Initial onboard clock generator if Early_Init_Onboard_Generator is defined. See
also POST 26h.
17h Reserved
18h Detect CPU information including brand, SMI type (Cyrix or Intel) and CPU level
(586 or 686).
19h Reserved
1Ah Reserved
1Bh Initial interrupts vector table. If no special specified, all H/W interrupts are directed
to SPURIOUS_INT_HDLR & S/W interrupts to SPURIOUS_soft_HDLR.
1Ch Reserved
1Dh Initial EARLY_PM_INIT switch.
1Eh Reserved
1Fh Load keyboard matrix (notebook platform)
20h Reserved
21h HPM initialization (notebook platform)
22h Reserved
23h 1 Check validity of RTC value: e.g. a value of 5Ah is an invalid value for RTC
minute.
2 Load CMOS settings into BIOS stack. If CMOS checksum fails, use default value
instead.
24h Prepare BIOS resource map for PCI & PnP use. If ESCD is valid, take into
consideration of the ESCD’s legacy information.
25h Early PCI Initialization:
q Enumerate PCI bus number
q Assign memory & I/O resource
q Search for a valid VGA device & VGA BIOS, and put it into C000:0
26h 1 If Early_Init_Onboard_Generator is not defined Onboard clock generator
initialization. Disable respective clock resource to empty PCI & DIMM slots.
2 Init onboard PWM
3 Init onboard H/W monitor devices
27h Initialize INT 09 buffer
28h Reserved
29h 1 Program CPU internal MTRR (P6 & PII) for 0-640K memory address.
2 Initialize the APIC for Pentium class CPU.
3 Program early chipset according to CMOS setup. Example: onboard IDE
controller. Measure CPU speed.
2Ah Reserved
2Bh Invoke Video BIOS
2Ch Reserved
POST Code (Hex) POST Routine Description