• State TI Thinks Resolved
  • Locked Locked
  • Replies 3 replies
  • Answers 2 answers
  • Subscribers 32 subscribers
  • Views 346 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

DS80PCI402: Receiver Detection

AP
Intellectual 370 points
Part Number: DS80PCI402

Hello,

we are facing a power-up issue on a PCIe x4 link between mainboard and (FPGA based) PCIe add-in card where the DS80PCI402 is used as Re-Driver between mainboard slot and card slot (link is not getting established or in x1 only instead of x4).

The issue is (or seems to be) solved if we set the DS80PCI402 RXDET to Manual-Always-ON mode (by 1K pullup on the RXDET device pin).

Are there any drawbacks/disadvantages using this mode in systems where the actual add-in card may be a x1 card at some times and an x4 card at other times (this is not a battery powered system)?
What's the point about the receiver detection phase (LTSSM DETECT state) anyway? Isn't this all determined later on in the LTSSM POLLING/CONFIGURATION states?

Thank you.

  • 0
    TI__Guru* 88925 points

    Greetings,

    The purpose of the RX detection is to allow the end point to do its house keeping and when it is done it will turn on its receiver termination. PCI402 sees this and then it turns on its own RX termination so the root complex or CPU would see this and start polling session. Once polling gets started, if there is no response from the end point - within 24ms - CPU assumes we are entering compliance mode and starts with Gen1 compliance. 

    Negative side effect of the RXDET to always on is that within 24mS after PERST# released the end point should respond to polling versus where it can take its sweet time to turn on its RX detect and etc.

    Regards ,, Nasser

  • 0 in reply to Nasser Mohammadi
    Intellectual 370 points

    Thanks for your reply.

    But from the Re-Driver point-of-view, RX detection (and Re-Driver Receiver Termination Enable) is handled independently for each OUT/IN pair, right?
    And the RX detect pulses driven by the Re-Driver after power-up, are they guaranteed to be generated synchronously on all still-undetected lines? Or (for example) may the detect pulses start right away on one Re-Driver TX line and the detect pulses on the next Re-Driver TX line may appear a little later after power-up than on the first TX line (maybe synchronously, but delayed)?

    Thank you.

  • 0 in reply to AP
    TI__Guru* 88925 points

    Greetings,

    RX detection pulses on the outputs are synchronous and receiver termination detection is handled independently for each output/input.

    Regards ,, Nasser