 PCI Express switch (source code)

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= PCI Express switch
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A <PCI Express switch> routes transactions between <PCI Express> links in a hierarchy. In a conventional single-root arrangement, an upstream port connects toward the <PCI Express root complex>[root complex] and downstream ports connect toward <PCI Express endpoints>[endpoints] or further <PCI Express switches>[switches]. Software sees logical bridge relationships that describe this structure.<The PCI Express Port Bus Driver Guide HOWTO>[§2.2, root and switch ports]{ref}

For example, two devices can have separate downstream links while sharing one upstream link to the host. Their local links can operate independently, but simultaneous host-bound transfers compete for the upstream capacity. Adding ports does not manufacture unlimited <bit rate>[host bandwidth]. A <PCI Express switch> routes the interconnect's transactions; its role and addressing model differ from those of an Ethernet switch.

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