1: seek for RSDP (SIG: "RSD PTR ") -- main BIOS area below 1 MB
2: seek for RSDT (SIG: "RSDT")
3: determine table amount. -- (RSDT len -header)/ sizeof(table type: 32/64bits)
4: find MCFG table and check 0x24 - 0x28 <-- address="" configuration="" nbsp="" p="">
http://wiki.osdev.org/PCI_Express
http://wiki.osdev.org/RSDP
http://wiki.osdev.org/RSDT
After determining the MMIO base address and the total number of busses in the address space, you can read from the extended configuration address space. To access a specific register, you must use the following formula: Address = MMIO_BASE + { bus number[27:20], device number[19:15], function number[14:12], extended register number[11:8], register number[7:2], offset [1:0] }.
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