PCI Memory and I/O Space

[jrshust]

Hello all,

I have successfully read my UHCI controller's BAR4 which gave me 0xFFFFFFC1. I guess this suggests I need to map 0x03FFFFFF in the PCI I/O address space. Unfortunately, I am extremely confused on how to access this address space. Is there like a set of similar I/O ports to 0xCF8 and 0xCFC that I write the address to and then the data to?

I tried multiple google searches but I just ended up with results telling me to set the C/BE command lines to the bus and the AD lines to the bus. How do I access these lines and access the PCI I/O space? I have read the PCI wiki page and I am confused on how to proceed after configuration.

Thank you for your help.

[thepowersgang]

Solved on IRC.

When you write all ones to a BAR, it will return with only the bits you can change set (excepting bit 0, which is a flag)
Once you know what size the device's address space is (by the bits that remain zero) you can allocate space from the I/O address space and then write that new address to the BAR.
Now it is possible to use the normal IO functions such as inb/outb etc to access the device, by accessing the address you gave it in the BAR.

[jrshust]

Thanks thePowersGang!

Things are making sense now and I am reading the USB status register (yay!).