[LinuxPPS] ntp 'bugs'

[Udo van den Heuvel]

Rodolfo Giometti wrote:
>> Hmm. I had to look at the code in refclock_nmea...
>> Does the ldisc change work on the pps device so that it effects the
>> `connected` serial line?
>> This because the first time_pps_create in refclock_nmea is on the pps
>> device. Only when that fails we do a time_pps_create on the serial line
>> itself as a fallback.
> 
> But usually you have the serial line as the main PPS device and
> /dev/pps{N} as altrenate one. Is that rigth?
> 
>> Please enlighten us on the flow of the change in time_pps_create and the
>> correlation with e.g. the code in refclock_nmea.
> 
> Here the refclock nmea code:
> 
> +       msyslog(LOG_ERR, "refclock_nmea: found GPS source \"%s\"", device);
> +       if (time_pps_create(pp->io.fd, &up->handle) < 0) {
> +               /* Try the alternate PPS device */
> +                (void) sprintf(device, DEVICEPPS, unit);
> +               msyslog(LOG_ERR, "refclock_nmea: try alternate PPS device \"%s\"", device);
> +                fd = open(device, O_RDWR);
> +                if (fd < 0)
> +                       goto pps_error;
> +               if (time_pps_create(fd, &up->handle) < 0)
> +                               goto pps_error;
>         }
> +       else (void) sprintf(device, DEVICE, unit); /* just rebuild device's name */
> 
> I suppose file descriptor pp->io.fd is related to the serial line so
> in the above time_pps_create() the ioctl(source, PPS_CHECK) fails and
> the ldisc is changed returing error. This causes a an
> open("/dev/pps{N}", ...) and a new time_pps_create() on the PPS
> device.
> 
> Is that right?

Yes and no.
Your rationale is right, but the agreed patch, at this time, from the
bug at https://support.ntp.org/bugs/show_bug.cgi?id=610 is at
https://support.ntp.org/bugs/attachment.cgi?id=405.
There you see that there is *no* time_pps_create for the NMEA carrying
serial line because we expect PPS from the PPS devcie which is tried next.
Of course this can be changed!

Udo