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  1. #1
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    PCIe lanes confusion

    Considering the following scenario:

    A designer wants to connect 3 devices on a PCIe x4 finger edge connector, commonly found on mother boards. All 3 devices will be populated on the same PCIe card. One device has 1 port of 2 lanes i.e (1 x2 PCIe port) Remaining two devices have 1 port of 1 lane (1 x1 PCIe port) each.

    Scheme 1:
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    Scheme 2:

    Click image for larger version. 

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    I've seen scheme 1 in the datasheets of some PCIe switches. I want to know if a PCIe switch is really required in this case.

    What if we omit the switch and just split the PCIe lanes?

    Will it be a legit PCIe network?

    If yes then how will bus numbers be assigned?

    Kindly ask if there is a need for clarification.

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  2. #2
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    Re: PCIe lanes confusion

    PCIe spec says:
    Optional Link negotiation behaviors include Lane reversal, variable width Links, splitting of Ports
    into multiple Links and the configuration of a crosslink.
    So the question is if the peer (e.g. the motherboard's PCIe bridge) supports it. I guess, it won't.



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