PCI: Difference between revisions

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m int 0x1a PCI BIOS presence check, fix function selection to use AX instead of BX
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* computer supports both mechanism #1 and the memory mapped access mechanism
* computer supports both mechanism #1 and the memory mapped access mechanism


For BIOS systems, "int 0x1A, BX=0xB101 (PCI BIOS presence check)" will tell you if the system uses mechanism #1 or mechanism #2. If this function doesn't exist you can't be sure if the computer supports PCI or not. If it says mechanism #1 is supported you won't know if the memory mapped access mechanism is also supported or not.
For BIOS systems, "int 0x1A, AX=0xB101 (PCI BIOS presence check)" will tell you if the system uses mechanism #1 or mechanism #2. If this function doesn't exist you can't be sure if the computer supports PCI or not. If it says mechanism #1 is supported you won't know if the memory mapped access mechanism is also supported or not.


For UEFI systems, it's extremely safe to assume that mechanism #2 is not supported; and you can test to see if the computer supports PCI or not by checking to see if the "PCI bus support" protocol exists. If PCI is supported, there's no easy way to determine if (e.g.) the computer supports mechanism #1 or not.
For UEFI systems, it's extremely safe to assume that mechanism #2 is not supported; and you can test to see if the computer supports PCI or not by checking to see if the "PCI bus support" protocol exists. If PCI is supported, there's no easy way to determine if (e.g.) the computer supports mechanism #1 or not.
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