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Original question:

AM5728: When running PCIe Gen2 with two lanes

AM5728: When running PCIe Gen2 with two lanes(Again)

O.H
Mastermind 6370 points
Part Number: AM5728

Hi experts,

Let me check about PCIe on AM572x. My customer is considering to connect PCIe Gen2 devices to lane0 and lane1 of AM5728 PCIe, and run them on Gen2.

Q1:Is it possible to run both lane0 and lane1 in Gen2? For example, I am assuming the following configuration.

  • When using only SS1: SS1 runs both lane0 and lane1 in Gen2.
  • When using SS1 and SS2: lane0 on SS1 and lane1 on SS2 both run on Ge2.

I understand from TRM that SS1 and SS2 support Gen2 respectively. I think the following applies to "using SS1 and SS2", but I'm confused because it could be read as "one lane of SS2 or SS1 could work with Gen1".

"24.9.1.1 PCIe Controllers Key Features"
• Two PCIe (PCIe_SS1 and PCIe_SS2) operates Gen2 1-lane supporting either RC or EP with the possibility of one operating in Gen1 and one in Gen2.

Also, referring to the thread below, it looks like SS2 is not stable on Gen2.
e2e.ti.com/.../am5728-pcie-2x-lane-g2-mode-link-up-sometimes-fail

Q2:Therefore, is it recommended to use only SS1 and run lane0 and lane1 on Gen2?

If there is insufficient information or it is difficult to answer, it would be helpful if you could let us know.

Best regards,
O.H

  • 0
    Mastermind 6370 points

    Hi,

    Sorry for rush you. Is there any update? The customer is looking for an answer, so it would be helpful if you could tell us the status. If you have difficulty answering the part about this question, or if you can answer offline, please let us know which one.

    Best regards,
    O.H

  • +1 in reply to O.H
    TI__Mastermind 23125 points

    Hi OH, 

    Your understanding of Q1 is correct - when you configure PCIe as 2 port with 1xlane each, both ports can support Gen2. 

    On your second question, I do see separate reports that PHY2 may be more error-prone with customer board routings, when used in 2-lane mode. So we may expect some delay to root cause the issue. 

    regards

    Jian 

  • 0 in reply to jian35385
    Mastermind 6370 points

    Hi Jian,

    Thank you for your answer. I understood. We will be careful when using SS2, but will contact you again if we actually encounter any problems.

    Best regards,
    O.H