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PCI-PCI Bridge

Discussion in 'Electronic Design' started by smithodude, Sep 29, 2006.

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  1. smithodude

    smithodude Guest


    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.

  2. Ben Jackson

    Ben Jackson Guest

    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).
  3. smithodude

    smithodude Guest

    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.

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