Questions about PCI configuration space register writing

abstractmath · **Joined:** Mon Sep 07, 2020 5:50 pm **Posts:** 46

I've been working on adding a pci driver to my OS, and I've been following the guide here https://wiki.osdev.org/PCI, and I don't see anywhere in the guide where it says how to write to one of these registers? My guess is that you'd write to the config address register and then write to the config data register, but I'm not sure, and I don't know where to find the information on how to write to one of these registers.

foliagecanine · **Joined:** Sun Aug 23, 2020 4:35 pm **Posts:** 148

abstractmath wrote:

My guess is that you'd write to the config address register and then write to the config data register

If I understand you correctly, you are correct.

Writing a PCI register is very similar to reading it.
For reading it you do:

Code:

outl(0xCF8,pci_address);
inl(0xCFC);

For writing, you do:

Code:

outl(0xCF8,pci_address);
outl(0xCFC,value_to_write);

Note that you do have to do some bit shifting, etc, to read/write single bytes.
(Here's my code for writing a PCI byte)

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Questions about PCI configuration space register writing

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