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DS250DF230: Can the PPM Conter be used as a rate indicator?

user4779049
Expert 2355 points
Part Number: DS250DF230


Hi Team,

Please advise me on my questions bellows.

I want to distinguish if the input data is lower or higher then 4.9 Gbps.

Q1. Can PPM counter be used as a rate indicator?

Q2. If yes, are there any recommended register set up procedure?

Q3. If yes, how long do you need to wait until you access PPM counter after signal detection ivent?

Q4. If the input signal travels long trace, lone bits may be filtered out resulting improper PPM count.

    Under such circumstance, does the PPM counter reflects the appropriate data rate?

Mita

  • 0
    TI__Mastermind 37263 points

    Hi Mita,

    I have not used the PPM count before for this application, but it might be possible.  We can look into this and get back to you by the end of the week.

    Can you help advise on how you would be configuring the retimer?  Is the thought that you would configure it to lock to 4.9 Gbps data, but then if the retimer cannot acquire CDR lock, you would check if the data rate is above/below 4.9 Gbps?

    Thanks,

    Drew

  • 0 in reply to Drew Miller1
    Expert 2355 points

    Drew-san,

     

    Thank you for your prompt feedback.

     

    I consider supporting mulipled data rate such as 25.78125, 10.3125,  4.91520

    4.25、2.125, 1.25 etc.

    Bad fortune, I use 25 MHz as the reference.

    1. So I set the CDR in manual rate mode setting channel registers for VCO

                count (0x61 through 0x63) and PPM count (0x64 through 0x67)

            2. Wait for signal detect bit is asserted

            3. Then checking the LOCK indication bit for a while

            4. If some time elapsed before LOKC indication bits are asserted,

                 back to step 1, I try another data rate set

             5.  If the expected data rate is lower than 4.9 Gbps, set the device in RAW mode

                   under CDR un-locked state. 

    If the PPM counter value is reliable on step 3 (Signal detected but before the CDR lock)

    I can skip the data rate tries.

    So I ask this question.

     

    I want to know  if the device check the PPM error condition while proceeding CTLE adaptation.

    If so, PPM error status may be accurate.

    If PPM check is done without CTLE adaptation, PPM error stats may not be accurate.

     

    Mita

  • 0 in reply to user4779049
    TI__Mastermind 37263 points

    Hi Mita-san,

    I'm not sure if there's any way in your system to know which rates you might receive.  The retimer can support locking to two separate data rates using the same configuration.  If you know whether you will receive Ethernet or CPRI data rates, you could configure the retimer to lock to both 25.78125 Gbps and 10.3125 Gbps using the same configuration.  You could then have a separate configuration for 4.91520 Gbps and below.

    I'll experiment to see if PPM counter updates even if signal cannot be locked to.  I'll have an update for you this week.

    Thanks,

    Drew

  • 0 in reply to Drew Miller1
    Expert 2355 points

    Drew-san,

    Thank you for your feedback.

    I am looking forward to recive your test results.

    Mita

  • 0 in reply to user4779049
    TI__Mastermind 37263 points

    Thanks Mita-san,

    We're looking into this.

    Thanks,

    Drew