[time-nuts] GPS for ntp
tic-toc at bodosom.net
Tue Oct 21 09:01:09 EDT 2014
Perhaps the programmable realtime unit (PRU) is what you're looking
for. It's used in the 5370 CPU replacement.
On Tue, Oct 21, 2014 at 8:33 AM, Neil Schroeder <gigneil at gmail.com> wrote:
> 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.
> On Mon, Oct 20, 2014 at 11:56 PM, Andrew Rodland <andrew at cleverdomain.org>
>> On Mon, Oct 20, 2014 at 10:50 PM, Neil Schroeder <gigneil at gmail.com>
>> > 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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