[time-nuts] GPS for ntp

Neil Schroeder gigneil at gmail.com
Tue Oct 21 08:33:15 EDT 2014


Andrew-
I'm actually referring to using either the eCAP function or one of the
integrated dmtimer triggers - which are, from some accounts, more accurate
than a gpio.

Google beaglebone dmtimer pps.

NS

On Mon, Oct 20, 2014 at 11:56 PM, Andrew Rodland <andrew at cleverdomain.org>
wrote:

> 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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