[time-nuts] GPS for ntp

Iain Young iain at g7iii.net
Tue Oct 21 08:54:50 EDT 2014


It's been done on FreeBSD. See:

http://lists.freebsd.org/pipermail/freebsd-arm/2013-February/004769.html


Patch is now in recent FreeBSD releases/snapshots

And yes, it's far superior to than using the GPIOs, or UARTS

There was some work done on Linux, but I'm not sure it was ever finished
or published.

All of my "Timing" Beaglebones run FreeBSD, with the exception of the
TIC stufff I wrote for the PRUSS's. As soon as the userspace bits of
that work on FreeBSD, I'll probably switch that to FreeBSD as well.


All the Best

Iain

On 21/10/14 13:33, Neil Schroeder wrote:
> 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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