Re: Using gpsd

On Tue, Mar 19, 2024 at 11:48:24PM -0700, Bill Unruh wrote:

> > FWIW, I'm testing a daemon that reads an *i2c* gps device and
> > feeds to chrony, and I need to bias it by about 0.250s -- I think
> > it is just that slow to read the bytes from i2c. But I'm still
> > looking for a foolish logic error like you suggest.

> That would surprize me very much, unless you are doing a very slow
> polling of the gps pps. .125 sec sound like the original IBMPC I
> bought in 1980.  Maybe if you told us the hardware you are using and
> the OS you are using someone could help more. Now if it is not PPS
> but is rather reading the NMEA, then a slow baud rate could give you
> that, since the sentences can be about that long at 600Bd. Also, you
> really only need the NMEA for the first few seconds until the system
> knows the seconds.

I can't (easily) use the PPS line because it's a separate pin, not
available over i2c. So yes, collecting NMEA lines.

Hardware: Raspberry Pi 3B+ with this gadget:

https://learn.adafruit.com/adafruit-mini-gps-pa1010d-module

running legacy (32 bit) raspbian, and my hack here:

https://gist.github.com/nobrowser/285d63410b9c2aec77a53587020cf2b6

I still want to try reading i2c with a super-slim C program instead,
but I'm not too optimistic about it.

-- 
Ian

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