Specifications

AMD Geode™ GeodeROM Functional Specification 75
PCI Support
32087C
7.1 INT 1Ah, Function B1h PCI BIOS Subfunctions Descriptions
GeodeROM supports real (INT 1Ah) and 32-bit protected mode access to the set of functions defined in revision 2.1 of the
PCI BIOS Specification. This section lists those INT 16h Function B1h subfunctions supported in GeodeROM, the parame-
ters that system software supplies to each subfunction, and the values that each function returns.
7.1.1 Subfunction 01h - PCI BIOS Present
Description:
The primary purpose of this function is to signal the presence and revision level of the system’s PCI BIOS. Additionally,
PCI BIOS Present reports the actual hardware mechanism the PCI BIOS uses to read and write configuration space
registers, as well as what type of special cycle support exists in the chipset.
Passed:
Returns:
If the PCI BIOS Present function returns successfully (CF = 0), the AL register contains Geode South Bridge device-spe-
cific information regarding special cycle support and the programming mechanism the system’s Geode South Bridge sup-
ports.
Parameter Description
AH B1h (PCI Function ID)
AL 01h (PCI BIOS Present)
Parameter Description
EDX 20494350h (4-byte ASCII string ‘PCI ‘) if PCI BIOS present
AH If 00h, and CF and EDX are correct, PCI BIOS is present
AL Supported hardware mechanism
BH BCD-encoded major revision of interface supported
BL BCD-encoded minor revision of interface supported
CL Zero-based number of last PCI bus in the system
CF 0 if PCI BIOS is present, and AH and EDX are correct
1 if PCI BIOS is not present
Table 7-2. AL Register Upon Return From A Successful Call to PCI_BIOS_PRESENT
Bit Description
7:6 Reserved
5 1: Special cycles are supported via Mechanism #2
4 1: Special cycles are supported via Mechanism #1
3:2 Reserved
1 1: System chipset supports Mechanism #1
0 1: System chipset supports Mechanism #2