PCI-PCI Bridge


If a system contains a PCI-PCI bridge with an arbitrary PCI device (call it Device X) on the furthest PCI bus (the bus most remote from the Host Processor) how is the Configuration space of Device X 'discovered' by the OS on startup? I understand that the IDSEL pin of Device X must be hard wired (via a resistor) to a high order address line, but how does the PCI discovery software actually find this configuration space if it doesn't know which address IDSEL is wired to? Does the OS need to be informed of the absolute address of the config space of remote devices?

I am running VxWorks on a DY4 board. My fellow software engineer has written code (I can't remember which function calls he used) that lists all the 'discovered' PCI devices. Device X is NOT amongst them.

Thanks Matt

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I don't recall the exact rules, but the two low address bits during config cycles let you look "through" bridge-type devices. It's explained in the PCI spec (google it, it's out there).

Ben Jackson AD7GD

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Ben Jackson

Ok, thanks Ben. I can recall something about that now but I guess I haven't quite understood it properly. I've got a PCI spec at work so can inspect that again.

Cheers Matt

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