Re: [pci] question on PCI master

[sumnow <sumnow@263.net>]

this is system specific. let me show you an example:

there is a pci master in northbridge in intel pci system. when software want to write 0xABCD to a pci device's memory or register such as a video card's video memory. suppose the destination address is 0x12345678. software uses instructions
  mov eax, 0x12345678
  mov ebx, 0xABCD
  mov [eax], ebx

when cpu executes the last instruction, it sends address 0x12345678 to MMU, MMU knows this address belongs to PCI system so redirects it to northbridge. pci master in northbridge will initiate a pci transaction on pci bus with address 0x12345678 and video card knows this is its own space and will assert DEVSEL# to response.

in addition, northbridge can do address remapping if neccessary.

in risc machine on which my work is based now, the instructions accessing pci device is LOAD/STORE.

i hope this helps.

sumnow

>Hi!
>
>COuld anyone here tell me how the PCI master know what is the 
>destination address when it want to initiate a write transfer? It seems 
>that the specification doesn't specify how to get the address. 
>
>Awaiting your reply
>with regards
>
>Wilton
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