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DP83822H: loopback test by BIST

Toshihiro Watanabe
Genius 10235 points
Part Number: DP83822H

Hello,

In Appendix B of snla266.pdf, B8 is to start then B9 check the status.

In B9, read address 0x0016[11:9] but we couldn't understand the meaning this.There is a locked or synced in register map.

Would you explain what is aiming B8 and B9?

How do we know the finish the test (ok or fail) if we select single mode in address 0x0016[14]?

We think there are 6 portions to loopback. Can each loopback do BIST test or is there any loopback can't check by BIST?

Best regards,

Toshihiro Watanabe

  • 0
    TI__Mastermind 19780 points
    Hi Watanabe-san,

    The purpose of reading register 0x16[11:9] is to ensure a few thing.
    1. The PRBS is locked (bit[11]). This means the BIST transmitter is sending packets, and the BIST receiver is receiving them and verifying the pattern is correct.

    2. The PRBS checker(receive block) has not lost sync (bit[10]). This bit will latch high if the PRBS stream is disturbed. If a channel has low quality, but not constant errors, this bit may be toggling to fast to see with slow register reads. So this bit indicates if the PRBS lock was lost at any time since last register read.

    3. The PRBS transmitter is actively transmitting packets (bit[9]).

    There is no finish of the test, you can run the packet check as long as you like. We generally run about 1M packets for a basic check. That would take approximately 2 minutes assuming maximum packet length and minimum IPG. If you receive no errors within 2 minutes, the link is very good.

    The BIST can be run in all loopbacks except far-end. In far-end, the PHY just retransmits any data it receives.

    Best Regards,
  • 0 in reply to Rob Rodrigues
    Prodigy 10 points
    Hello,

    Thank you for your anwer.
    I have additional questions.

    [Q1]
    When does "BIST Error Count" count up?
    (BIST Error Count: BICSR1(0x001B) bit[15:8])

    [Q2]
    We tried to check loopbacked packets using MAC (not BIST).
    Is the following procedure correct?

    1. Set to Digital-Loopback mode by BISCR (0x16).
    2. Send packets from MAC (not BIST)
    3. Receive the loopbacked packets at MAC.

    Best regards,
    Iketo
  • 0 in reply to user5835526
    TI__Mastermind 19780 points
    Hi Iketo,

    Q1. It counts up when the PRBS checker finds an errored byte in the data stream the PRBS generator is creating. This is very rare.

    Q2. Yes, the procedure is correct, but BIST must not be on if the MAC is sending packets.

    Also note about loopback when the MAC is the data source, PING does not work. PING requires the far-end link partner to make changes to the packet for the MAC to understand it is successful. The PHY cannot make the changes to the packet to achieve this.

    Best Regards,