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what does "host bridge" mean?

Discussion in 'Embedded' started by John Black, Aug 10, 2004.

  1. John Black

    John Black Guest

    I am looking into some PCI document for the development board I have, in
    PCI section it mentions a lot a word, "host bridge", what exactly does
    this mean? Google only gives me a bunch of products, I want to know
    where I can find the terminlogy explanation.

    Thanks.
     
    John Black, Aug 10, 2004
    #1
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  2. John Black

    £¢$¥ Guest

    I'm sure that people more experienced that I will correct me, but when I was
    working with PCI, on the platform that I worked with the "host-bridge" was
    an IC that served as bridge between the PowerPC data bus and the PCI data
    bus.
     
    £¢$¥, Aug 10, 2004
    #2
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  3. That's the right general idea. More commonly, the implementation only takes
    up part of a chip, such as one of the support chips in an Intel architecture PC,
    or it's just built into the processor, like in the more highly integrated PPC chips.
    But it is indeed a bus conversion from a processor bus to a PCI bus. Lets a
    bus-master PCI card access memory on the other side.
     
    David Kinsell, Aug 11, 2004
    #3

  4. The "Host Bridge" is what connects the tree of PCI busses (which are
    internally connected with PCI-to-PCI Bridges) to the rest of the
    system. Usually the processor(s) and memory are on the "other" side
    of the Host Bridge.

    On typical PC implementations, this function is embedded in the North
    Bridge.
     
    Robert Wessel, Aug 11, 2004
    #4
  5. : That's the right general idea. More commonly, the implementation only takes
    : up part of a chip, such as one of the support chips in an Intel architecture PC,
    : or it's just built into the processor, like in the more highly integrated PPC chips.
    : But it is indeed a bus conversion from a processor bus to a PCI bus. Lets a
    : bus-master PCI card access memory on the other side.
    :
    :
    :> I'm sure that people more experienced that I will correct me, but when I was
    :> working with PCI, on the platform that I worked with the "host-bridge" was
    :> an IC that served as bridge between the PowerPC data bus and the PCI data
    :> bus.

    Correct. A bridge between the sytem Local Bus and the Peripheral Component
    Interconnect (PCI) bus.

    But there is more to it - there might be multiple local bus to PCI bridges
    in the system. There might even be mulitple PCI buses connected either
    transparent (hierarchal) or non-transparent. There might even be completely
    different buses in the system, like ISA or VME. All of them require access
    to the PCI bus and system memory, otherwise they wouldn't be there in the
    first place. Most of them even require bus master privileges. And it is the
    responsibility of the 'host bridge' to do the arbitration between the
    different contenders for PCI bus time slices. Interrupt steering should
    have been here too, but more often than not isn't.


    --
    ******************************************************
    Never ever underestimate the power of human stupidity.
    -Robert Anson Heinlein


    ******************************************************
     
    Geir Frode Raanes Sørensen, Aug 11, 2004
    #5
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