[LinuxPPS] Linux 2.6.28 - serial time string jumps

[Hal V. Engel]

On Thursday 15 January 2009 06:29:47 Heiko Gerstung wrote:
> OK, new day, new problem...
>
> Warning: This might be a little bit offtopic i.r.t. linuxpps, but I have
> seen that you guys are dealing with bleeding edge versions of the
> kernel, linuxpps and ntp (just like me) and might have similar
> experiences...
>
> I am trying to test the new kernel with Rodolfo's linuxpps patch against
> ntp-4.2.4p6 ... PPS now works reliably but what I see is that the time
> of my GPS string reference (parse driver) is sometimes jumping for 3-4
> ms, resulting in being called a bad ass falseticker by ntpd and striked
> out (x). This in turn leads to the PPS source being rejected and after a
> short while (I am dealing with 16s polling intervals) everything seems
> to kick back to normal ...
>
> The same hardware performs good under 2.6.15.1 (the last kernel version
> I was working on), back then with the PPSLight patch from Ulrich Windl.
> While I assume that PPS is working great here, I wonder if anyone has
> experienced jumps and latency issues on their serial ports with 2.6.28?
>
> I know that I had some successful tests with 2.6.24 but I wanted to use
> a more recent kernel ...
>
> Regards,
>  Heiko

Have you tried: 

setserial /dev/<your port> low_latency

This should make the latency of the serial port lower and also more 
consistent.   I have not seen this issue with any of the machines I have this 
on.

Hal