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PCI Express over Optical fiber

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Newbie level 5
Nov 20, 2008
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Hello forum,

I want to connect an FPGA board to the PC with an external PCI Express solution.
We did this before with MOLEX PCI Express expander connectors and cables using a PERICOM PCI Express re-timer.
Now we want to go longer distances and decided to use optical fiber with an SFP connector.
Connection is one lane, 5Gb/sec.

My questions are:

1 - The Adapter board in the PC is not capable of routing clock to the FPGA board.
We will generate the clock on the FPGA board with a precision clock. Is this OK?

2- The traces between PCI express connector and SFP is short.
Do we still need a PCI Express repeater with Equalization and De-Emphasis like DS80PCI102.


Standard PC PCI implementationa are using a common reference clock architecture. This allows for SSC (spread spectrum clocking) without jitter issues. Presuming that the PC side is using SSC, your need to implement a data clocked architecture with good jitter tolerance. But I don't know if the PC side interface is prepared for it at all.

I don't see a need for a PCI express repeater, just proper level conversion.

Thank you very much. It helped a lot.

PCI Express (Peripheral Component Interconnect Express), officially abbreviated as PCIe, is a high-speed serial computer expansion bus standard designed to replace the older PCI, PCI-X, and AGP bus standards. PCIe has numerous improvements over the aforementioned bus standards, including higher maximum system bus throughput, lower I/O pin count and smaller physical footprint, better performance-scaling for bus devices, a more detailed error detection and reporting mechanism (Advanced Error Reporting (AER) [1]), and native hot-plug functionality. More recent revisions of the PCIe standard support hardware I/O virtualization.

By Optoroute

A PCIe card fits into a slot of its physical size or larger (maximum ×16), but may not fit into a smaller PCIe slot (e.g.,a ×16 card in a ×8 slot). Some slots use open-ended sockets to permit phycally longer cards and negotiate the best available electrical connection. The number of lanes actually connected to a slot may also be less than the number supported by the physical slot size.
An example is a ×16 slot that runs at ×4. This slot will accept any ×1, ×2, ×4, ×8, or ×16 card, but provides only ×4 speed. Its specification may read: ×16 (×4 mode); "×size @ ×speed" notation (×16 @ ×4) is also common. The advantage is that such slot can accommodate a larger range of PCIe cards without requiring motherboard hardware to support the full transfer rate.

By Optoroute, quote from Optoroute blog.

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