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DP83867E: Alignment of RX/SFD and TX_SFD to first octet of preamble

Alexander Ockert
Prodigy 70 points
Part Number: DP83867E


Hello together,

we are evaluating DP83867 für Industrial Ethernet usability.

I have a question regarding RX and TX SFD pins:

Is it possible to re-align RX_SFD/TX_SFD pulse generation at Start-Of-Stream (when first octet / nibble of Ethernet Frame preamble is received/transmitted) instead of pulse generation when SFD is received/transmitted/?

BR, Alex

  • 0
    TI__Mastermind 27232 points

    Hi Alex,

    This is not possible as far as I know. Can you explain why you are trying to do this?

    Thanks,

    David

  • 0 in reply to David Creger
    Prodigy 70 points

    Hi David, there are 2 reasons:

    1) When you do 1-step sync forwarding regarding IEEE802.1AS you have to take the transmit timestamp, do some calculation with it and add this timestamp into the current frame at a specific position within the same frame. If the timestamp is taken at the start of stream (1st octet of preamble) instead at SFD you have 8 octets more time to do all these things. Especially at GBit speed there is not much time.

    2) Timestamping at SFD (also called SMD-E regarding IEEE802.3)  limits timestamping to Express frames, not for preemptable frames with a SMD-S0..3. So you can never timestamp frames that are received via PMAC (Preemptable MAC).

  • 0 in reply to Alexander Ockert
    TI__Mastermind 27232 points

    Hi Alex,

    Understood. Unfortunately there is no way to change this so you will have to make do with the current location of the SFD pulse. 

    Thanks,

    David