[time-nuts] GPS for ntp

Andrew Rodland andrew at cleverdomain.org
Tue Oct 21 02:56:54 EDT 2014

On Mon, Oct 20, 2014 at 10:50 PM, Neil Schroeder <gigneil at gmail.com> wrote:
> The one thing that hasn't yet happened is making the beaglebone timestamp
> on the linux side in a way that works for ntp.
> Custom code no problem. Freebsd PPSAPI no problem. Linux, nothing there
> yet.
> I have been working on it but if anyone has some insight its appreciated.

It appears to support gpio class devices, with interrupts, so the
pps-gpio driver (in-tree since 3.2) should work just fine. The only
thing that's needed (other than building the driver) is a bit of code
in the board support file to register the device. Various folks have
done it for the rpi (http://ntpi.openchaos.org/pps_pi/ for example),
and I've done it for the UDOO Dual
(https://gist.github.com/arodland/518f037e4f24b1984286). The BBB is
probably about as easy.

I'm not sure if there's other hardware that lets you do better than
grabbing an interrupt, but that will get you in the microsecond range
or a bit better, anyhow.

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