Re: [chrony-users] RTOS with Chrony/GPS - worth considering ?

[John Miller <john@xxxxxxxxxxxx>]

Hi Laura,

I have a project you may be interested in. It's a Raspberry Pi hat with a GPS and RTC, and the PPS line from the GPS is used to discipline chrony through gpsd.

There's more info here:

https://millerjs.org/timehat

There are a number of ways to do this other than my project, but it may be a useful jumping off point.

I have done some experimenting with an RTOS, but I haven't found it to make any difference at all. Both Debian and Alpine linux have performed very well for me. Likewise, using an augmentation service won't help for timing - they're really just for positioning. 

Regards,

John

On Mar 5, 2022, at 7:39 AM, Laura Smith <n5d9xq3ti233xiyif2vp@xxxxxxxxxxxxx> wrote:

Hi

Apologies if this is a question which has been asked before or is not suited to this list.

I'm planning to setup a GPS backed timeserver, and my understanding is that the "best" way to do this currently is to use GPSd + chrony to get GPS + 1PPS.

Reading up a little on the details, my understanding is that the 1PPS part works by generating interrupts on the server either via GPIO or COM Port DCD pin.

This then raised the question in my mind as to whether choice of OS was important. In particular whether the use of an RTOS platform (e.g. FreeRTOS) would be beneficial given that the internals of na RTOS mean it is better setup for dealing with interrupts in an efficient and timely manner ?

So in a nutshell, would the use of an RTOS be un-necessary premature optimisation or genuinely useful ?

I also have a second question. Is there any point using an augmentation service (i.e. NTRIP, PPP, SBAS and the like) in a timing context ?  Or are they only useful in a positioning context ?

Thanks !

Laura

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