[time-nuts] GPS for ntp

Iain Young iain at g7iii.net
Tue Oct 21 10:14:38 EDT 2014


It just turns up as /dev/pps0 like any other PPS source, so you
configure ntp in the same way you would for any other PPS source,
or build ppsapitest to test it manually

(Although be aware you -may get a Invalid argument error from
ppsapitest after running it more than once. Reboot solves it,
and since the BBB's don't do anything else, and I don't restart ntp
too often, its not a big deal for me.)


Iain
On 21/10/14 14:58, Simon Marsh wrote:
> Iain,
>
> How do you map the timer counter value in to a PPS timestamp ?
> (that is, how do you turn the HW counter value in to what the OS thought
> the time was when the event occured ?)
>
> Cheers
>
>
> Simon
>
>
> On 21/10/2014 13:54, Iain Young wrote:
>> 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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