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Altera_Forum's avatar
Altera_Forum
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10 years ago

PCIE Gen1 and Gen2 negotiation

I've got a board, that sometimes powers up with the BIOS recognising 4 lanes at Gen 2 and sometimes the BIOS only recognises 4 lanes at Gen 1. I'm using a Cyclone 5 CST part, and the hard IP controller with Avalon ST. Is there any reason why I'm not consistently getting Gen 2?

Cheers,

Simon

3 Replies

  • Altera_Forum's avatar
    Altera_Forum
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    10 years ago

    Probably some signal integrity issue causing the Gen2 data rate to fail during negotiation.

  • Altera_Forum's avatar
    Altera_Forum
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    10 years ago

    I've encountered this problem at my previous workplace repeatedly.

    For a starter, take a closer look at your AC coupling capacitors, to see if any are either damaged or missing (for a 4x PCIe you should have 8 of those).

    Another failure may arise from a damaged connector - the connector must be clean without any signs of scratches.

    Report back when you have a chance,

    Refael.
  • Altera_Forum's avatar
    Altera_Forum
    Icon for Honored Contributor rankHonored Contributor
    10 years ago

    Agree with Refael, the connection issue might lead to signal degrade as well.