> -----Original Message-----
> From: Richard Cochran [mailto:richardcoch...@gmail.com]
> Sent: Dienstag, 18. August 2020 23:12
> To: Jacob Keller
> Cc: linuxptp-users@lists.sourceforge.net
> Subject: Re: [Linuxptp-users] Can ptp4l be used without phc2sys?
>
> On Tue, Aug 18, 2020 at 02:47:20PM -0700, Jacob Keller wrote:
> > On 8/18/2020 12:40 PM, Irene Kravets wrote:
> > > I am using vendor kernel and a vendor-specific PTP driver
(drivers/net/Ethernet/freescale/fec_ptp.c). I see this > driver in the
mainline kernel as
well. What enables PPS output signal is the PTP_ENABLE_PPS ioctl sent from
linuxptp >
stack (in phc2sys.c).
> >
> > It's possible the driver assumes "PTP_ENABLE_PPS" is for enabling the
> > PPS output signal. I know I've had plenty of discussion with colleagues
> > trying to explain the difference between PTP_ENABLE_PPS and
> > PTP_PEROUT_REQUEST... So I would imagine other vendors might also get
> > this wrong sometimes.
>
> I did review that driver back in 2014, and I think they are using a
> capture/compare register on some signal from the MAC. They adjust the
> registers after every second in SW, with the instantaneous frequency
> adjustment. I told them it wouldn't work well.
Can you expand on this Richard?
Yes the fec_ptp driver isn't great, but the timestamps are done in hardware, so
latency/jitter
in the ISR isn't relevant - is it? The fec_ptp driver may not be reporting
capabilities
correctly (it just sets most of them to zero). And of course, there are so many
different
boards where this is used - some can do PPS-IN & OUT, but there's no PPS-IN in
fec_ptp, as
I recall.
>
> I guess that the physical signal they are using just happens appear as
> an output, or maybe the vendor kernel has extra code to make that
> happen.
Device tree to configure GPIOs and PADs - connect external pins to
Capture/Compare in iMX
Richard Hill
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