linuxptp-users

[Linuxptp-users] Inexpensive ARM board for a PTP server (using GPS PPS)?

[Mark H. <ma...@ha...>]

I have a GPS 1PPS signal available and would like to use it to
distribute time across my home network.  The more accurate the better.

GPS ----> single-board computer ------> several PTP client hosts
    1PPS                       ethernet

I see that the TI AM355x boards like the Beaglebone Black have an
ethernet driver with hardware timestamp support, but I also found
some references on this mailing list to a silicon bug affecting the PTP
clock?  Assuming that's still the case, what limitations does it
impose?

I haven't procured any hardware yet.  Is there another animal- or
fruit-board SBC with better PTP support that I should be looking at?

If I do go with the Beaglebone, will a recent mainline kernel get me
everything I need (current PTP drivers, PPS input on a GPIO pin)?

Thanks,
Mark

Re: [Linuxptp-users] Inexpensive ARM board for a PTP server (using GPS PPS)?

[Richard H. <pl...@gm...>]

> I have a GPS 1PPS signal available and would like to use it to
> distribute time across my home network.  The more accurate the better.
>
> GPS ----> single-board computer ------> several PTP client hosts
>     1PPS                       ethernet
>
> I see that the TI AM355x boards like the Beaglebone Black have an
> ethernet driver with hardware timestamp support, but I also found
> some references on this mailing list to a silicon bug affecting the PTP
> clock?  Assuming that's still the case, what limitations does it
> impose?
>
> I haven't procured any hardware yet.  Is there another animal- or
> fruit-board SBC with better PTP support that I should be looking at?
>
> If I do go with the Beaglebone, will a recent mainline kernel get me
> everything I need (current PTP drivers, PPS input on a GPIO pin)?
>
> Thanks,
> Mark


Bear in mind Mark that PPS-in via GPIO might not give great results - far too much jitter 
& latency.  Some hardware (eg iMX6 boards I have used ) allows PPS-In
to be connected directly to dedicated registers which I found to work well.
(The standard kernel driver needs extensive rework to do this however)

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Re: [Linuxptp-users] Inexpensive ARM board for a PTP server (using GPS PPS)?

[Miroslav L. <mli...@re...>]

On Tue, Feb 05, 2019 at 05:33:51PM -0800, Mark Haun wrote:
> If I do go with the Beaglebone, will a recent mainline kernel get me
> everything I need (current PTP drivers, PPS input on a GPIO pin)?

IIRC the PTP support for the BBB is not in the mainline kernel and it
was using the legacy timestamping API.

The best cheap HW for timekeeping that I know of is the PC Engines
APU. It has two I210/I211 ports, which are well supported in the
kernel and work very well for timekeeping. The board even has some
pads for the SDPs, which enable an extremely accurate PPS
timestamping.

Here is a blog post showing how this HW can be used for NTP. The same
could be done with PTP. (There is actually a related discussion on the
-devel list about adding the PPS support to phc2sys)

https://blog.dan.drown.org/apu2-ntp-server-2/

-- 
Miroslav Lichvar