Hi everyone,

Installed chrony today (TinyCore 3.8_4, 2.6.33.3), it synchronizes to the "pool" servers but doesn't make use of my attached GPS receiver. The GPS receiver is "ttyACM0", the PPS output goes into "ttyS0".

I also tried gpsd with ntpd and there again, ntpd couldn't see the PPS.

I start chrony with; sudo /usr/local/etc/init.d/chrony start

And then start gpsd with; gpsd -D 5 -N -n /dev/ttyACM0

I've tried two different chrony.conf files and neither one works, see attached.

In both cases, the only PPS related output I can see from gpsd is;

gpsd: PROG PPS Create Thread gpsd_ppsmonitor
gpsd: PROG PPS can not connect chrony socket: /tmp/chrony.ttyACM0.sock

Can anyone tell me what I'm doing wrong here ? (I'm sure it's many things).

I just really hope I don't have to build a new kernel with CONFIG_PPS enabled, in 2.6.33.3, it's not selected by default.

Thanks,

David

What is the make and model of the GPS receiver?

Hi Gad, it's a U-Blox EVK-M8T

Time is complicated...

If your PC has a hardware serial port i.e ttyS0 why not switch the receiver to send data using its UART versus USB?

Have you checked the PPS signal using ppscheck to see if the receiver output is good? ppscheck should be included with the gpsd utilities.

ppscheck /dev/ttyS0

gpsd automatically creates the pps0 device that is associated with the serial port on the command line but I am not sure how to switch it to another port or if it is possible.

You might need to rebuild the kernel with PPS support.

https://gpsd.gitlab.io/gpsd/gpsd-tim...#_introduction

Hi michaelk,

Thanks, I slowly clued in to trying that as well, I'm going to try sending the NMEA **and** PPS out the serial port of the EVK-M8T, input to ttyS0 on my PC, and hope that gpsd will pick up everything that way. Not really knowing what I'm doing, I've been trying to replicate what another fellow setup for me sometime ago and he used the USB ports on the receiver and PC for NMEA (ttyACM0) only and the serial ports on the receiver/GPS for PPS.

However, as you suggest, I think I can get both the NMEA and PPS over the serial port, I just need to make up the cable and will try that shortly.

Thanks for the help.

David

Hi michaelk,

I got the U-Blox setup to output NMEA and PPS over the serial port, made up a new RS232 "straight-thru" cable, cut up the USB cable so the USB port only powers the U-Blox, used the SHM definition in chrony.conf, pointed gpsd at /dev/ttyS0, and voila, chrony is happy ! !, using both the NMEA and PPS info on the serial port !

Last night, chrony was able to sync the time on the Vortex DX3 to generally better than 1 us !, usually between 500 and 800 ns !!

So now I just have to figure out how to get this all going on boot-up, and also tweak some parameters, right now the "offset" for the NMEA time is too small, I think chrony won't use any time source more than 200 ms "off" or something..

But, first thing will be to getting chrony and gpsd fired up on boot-up, and then can do the tweaking after, I'm just very relieved it doesn't look like I will need to rebuild the kernel or anything, thank goodness.

Thanks for the help,

David

Excellent, I would be interested in see if there was a difference between chrony and ntpd. I could not find any good information except for the Pi on using a separate PPS input.

I am interested since I built a similar setup with a Garmin 18x GPS receiver many years ago but the computer that I used died and so it is not being used at the moment.