Re: [chrony-users] Debugging PPS messages in chrony

Rob,

I know that an absolute source of time information is necessary, I just figured there would be some indication of PPS being received by chrony. Note, this is not actually a GPS, and the PPS line is going to a GPIO pin, as a result I do not believe ldattach is necessary following http://paul.chavent.free.fr/pps.html.

I don't entirely understand the last point, my understanding was that it is chrony who creates the SHM/socket depending on the configuration, in this case how can I start the SHM program before starting chrony? The motivation of the original question is that without some confirmation that at least the PPS is received, it becomes very difficult to debug with PPS+SHM simultaneously, if this doesn't work immediately (which it didn't). Do you have any suggestions for how to proceed?

Best regards,

Morten

On Mon, Jul 8, 2024 at 6:06 PM Rob Janssen <chrony-users@xxxxxxxxx> wrote:

Morten

You cannot have only a PPS source, because that does not give you absolute time information, only modulo-1-second information.
So when you use PPS you always need to add another source.
That can be a network source (NTP) with server or pool, or you can use a serial port (NMEA) to the GPS device.
When you have internet or the PPS source provides NTP, it is preferable to use that.
It is also possible to use SHM for that, but you need another program that puts the time info into SHM.
Furthermore, when you start things using systemd it is tricky because systemd provides no sequence of starting
daemons, and you have to start the program for SHM and the pps (ldattach) BEFORE starting chrony!

Rob

On 2024-07-08 10:07, Morten Nissov wrote:
> Hi all,
>
> I am looking at setting up a relatively custom thing for timekeeping, which attempts to function as a GPS (in terms of PPS + unix stamp) using an RTC and microcontroller.
>

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