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AM335X: 1588v2 PPS output

Dave Berg
Prodigy 40 points

We're using 1588v2 with our AM335x Starter Kit (TMDSSK3358) and need to enable PPS output so we can measure accuracy.

Configuration:
 - Default images provided by the AM335X SDK version 03.01.00.06 (PROCESSOR-SDK-LINUX-AM335X 03_01_00_06) using provided script 'create-sdcard.sh'
 - Running ptp4l with eth0 (runs as slave to our GPS grandmaster)
 - Boot message reads "Arago 2016.08 am335x-evm ttyS0"

Questions:
1) How can we enable PPS output so we can compare it against our grandmaster's PPS on a scope?

2) Since both the AM335x MAC and the AR8031 PHY on the board are capable of timestamping, which one provides the timestamping in the current implementation as we are using it?

We tried monitoring the PPS output pin of the AR8031, but saw no transition, so it seems either the PPS output isn't enabled by default or the board isn't using the AR8031 for timestamping.

  • 0
    TI__Guru**** 393215 points
    The Ethernet experts have been notified. They will respond here.
  • 0 in reply to Biser Gatchev-XID
    Prodigy 40 points

    Hi Biser,

    After further research, it appears that the AM335x Starter Kit only uses the PTP clock provided by the CPTS (Common Platform Time Sync), which would explain why the AR8031 PPS isn't active.

    Is there a way to utilize the PTP clock in the AR8031 on this board?

    Our application requires certain features provided by the PTP clock in the AR8031, so the CPTS is a non-starter for us.

  • 0 in reply to Dave Berg
    Prodigy 30 points

    hi DAVE,

    I have the same question, have you finished?

  • 0 in reply to chao lei
    Prodigy 40 points

    No, I am still hopeful that TI support personnel will reply to let us know if there is a way to do either of the following:

    1) Utilize the AR8031 for 1588 timestamping, which should allow us to use its PPS output.

    2) Enable a PPS output of some sort for the CPTS.

  • 0 in reply to Dave Berg
    Prodigy 30 points

    I try to configure AR8031 registers, the relevant register tried a variety of combinations, but the PPS did not come out, what piece of configuration is wrong?

    Still not AR8031 problem, is a question of Linux driver?

  • 0 in reply to chao lei
    Prodigy 40 points

    Based on my understanding, the PHC in the CPTS is used by default, not the AR8031. As far as I can tell, there is no way to get a PPS output from the CPTS either.

    The reason the CPTS is used is apparently because there is no support in the AR8031 Linux driver (drivers/net/phy/at803x.c) for the AR8031's PHC and timestamping capability.

    Since the AR8031 PHC is not being utilized, there won't be any output on its PPS signal.

    If there is some way to get a PPS output from the CPTS I'd love to hear how.

  • 0 in reply to Dave Berg
    Prodigy 10 points
    Hi Dave,
    I'm dealing with the same problem. Do you have a solution since then?

    I'm using a DMTIMER to generate a periodic PPS output, with the "Hardware Time Stamp Push Event" function the CPTS module can generate a timestamp to the rising edge of the HWx_TS_PUSH input (this is the PORTIMERPWM output of the DMTIMER). I would like to read out the timestamp value from the CPTS Event FIFO which I could adjust the DMTIMER with, to fit it to the whole seconds of the PTP clock (CPTS'S timer).
    I still have problems with the timestamp acquisition.