Re: [Linuxptp-devel] Synchronize PWM to CPTS internal counter

[Yursen K. <ky...@gm...>]

Greetings! Thank you for your interest.

The basic idea is to adjust PWM output depending on the captured CPTS
timestamps, thus eliminating any software latencies.

1. Start DM timer free-running as a 1 sec period PWM.
2. Enable generation of CPTS hardware timestamp events on this timer.
3. On each CPTS HW_TS event, calculate the offset and change TLDR value.

One person (I am not sure I can tell his name) did some improvements to
this:

1. He starts PWM close to nearest second (from HW_TS_PUSH event), and uses
a simple PI controller for TLDR.
2. He also enables the actual PWM hardware output after a first few
adjustment pulses.

Best regards,
Kim Yursen

2016-11-30 23:59 GMT+03:00 David Cemin <dav...@co...>:

> Hi Kim,
>
>
> On this thread (https://www.mail-archive.com/lin...@li.../msg01033.html) you wrote this
>
>
> >We implemented PPS output signal through AM335x Dual-Mode Timer >running in
> >the PWM mode with SCLK frequency.
>
> >This is more accurate than software GPIO output because the CPTS >on the
> >AM335x
> >can generate hardware timestamp event on the rising edge of the >DMTimer,
> >making it possible to synchronize PPS with the CPTS internal clock <counter.
>
> Can you (or someone else on this list) give more details on how did you achieve this? Im not sure sure you actually got the pps output sync to PTP on this approach. How did you connect the CPTS to the PWM ?
>
>
> Thanks
>
>
> --
>
> David
>
>
>
>
>