[LinuxPPS] Occasionally ntpd stops receiving NMEA data

[Rodolfo Giometti]

On Mon, Jun 05, 2006 at 01:19:55PM +0200, Udo van den Heuvel wrote:
> 
> LINUXPSS_API is the variable to be checked by ntp.
> (i.e.: do we have LinuxPPS? to include the header files)

I don't think NTP should check against LINUXPSS_API. It should check
against PPS_API_VERS_1 or PPS_API_VERS_2 instead.

LinuxPPS is just an implementation of PPS API, so we should declare
the PPS API supported with a define like PPS_API_VERS_x and the
particular PPS implementation with the define LINUXPSS_API.

> Later ntp can check for PPS_API_VERS, PPS_API_VERS_1 or PPS_API_VERS_2
> (see how messy this gets).

I agree.

> Just PPS_API_VERS which can be either 1 or 2 for now should be enough.
> 
> Just send in a patch to the ntp folks and *maybe* the next release will
> behave differently.

This is a possibility but I don't think NTP folks will accept
something like this... they also refused modifying PPS API in order to
consider non serial connected GPS antennas...

> Then, when PPS_API_VERS 3 comes around there's less trouble.

I agree.

> Can we skip stuff like this and concentrate on the issues I posted about
> earlier?
> Like simplifying and minimizing the changes to the ntp code?

This stuff are important in my opinion, since future patches will
depend on these defines.

> Maybe put a function layer in between so there's no changes needed?
> (for the not LinuxPPS-aware applications)

About this topic I think we should open a new thread. However just to
init the discussion, here my proposal:

1) we should implement a new function:

   int time_pps_findpath(char *path, int pathlen);

2) The user should define a _symbolic_ link into his/her system as
follow:

   $ ln -s /dev/ttyS0 /dev/pps0

symbolic links don't require pointed file existence.

3) The drivers' patch should do something like this:

  +#ifdef PPS_HAVE_FINDPATH
  +      /* Get the PPS source's real name */
  +      fd = readlink(PPS_DEVICE, path, LINUXPPS_MAX_NAME_LEN);
  +      if (fd <= 0) {
  +              msyslog(LOG_ERR, "refclock: PPS source \"%s\" is not a valid link", PPS_DEVI\CE);
  +              return (1);
  +      }
  +      /* Try to find the source */
  +      fd = time_pps_findpath(path, fd);
  +      if (fd < 0) {
  +              msyslog(LOG_ERR, "refclock: cannot find PPS source \"%s\" in the system", PPS_DEVICE);
  +              return (1);
  +      }
  +      msyslog(LOG_INFO, "refclock: found PPS source \"%s\" at id #%d on \"%s\"", PPS_DEVICE, fd, id);
  +#endif   /* PPS_HAVE_FINDPATH */
  +
  +
         if (time_pps_create(fd, &pps_handle) < 0) {
  -              pps_handle = 0;
                 msyslog(LOG_ERR,
                         "refclock: time_pps_create failed: %m");
         }

Define PPS_DEVICE may be init as follow:

   #define PPS_DEVICE	"/dev/pps0"

In this manner we can surely address the right PPS device.

What do you think about it?

Ciao,

Rodolfo

-- 

GNU/Linux Solutions                  e-mail:    giometti at enneenne.com
Linux Device Driver                             giometti at gnudd.com
Embedded Systems                     		giometti at linux.it
UNIX programming                     phone:     +39 349 2432127
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