[ntp:questions] problem with ntpd refclock and pps via parallel port

David Lord snews at lordynet.org
Mon Feb 1 01:44:14 UTC 2010

David Lord wrote:
> problem with ntpd refclock and  pps via parallel port
> Hi
> on system A I had type 22 pps working ok from pps at ttl
> level to DCD of serial port. This was a bit erratic and
> temperature sensitive possibly due to mismatch of ttl/rs232
> levels.
> on system B, rather than add complication of ttl=>rs232
> conversion I've connected pps to parallel port and changed
> symlink to be /dev/pps0 => /dev/lpt0
> With same NetBSD-5-PPS kernel as on system A, I am getting following in 
> ntp.log at startup:
>   refclock_atom: /dev/pps0: Interrupted system call
>   configuration of failed
> No PPS shown by 'ntpq -p'
> A google for above here gave some messages from suggesting
> use of atppc* at isa?, ppbus* at atppc?, pps* at pps?
> so now I have dmesg with
>    atppc0 at isa0 ......
>    atppc0: capabilities=3<INTR,DMA>
>    ppbus0 at atppc0
>    lpt0 at ppbus0
>    pps0 at ppbus0
> System B, NetBSD-5, doesn't have a refclock, just other
> ntp servers but ntp docs appear to state this as being ok.
> On system C, NetBSD-4.0.1, which is working ntp server with
> MSF clock on serial via DCD, I've just tried link
> pps0 => lpt0 and have same output from ntpd as from system B.
> I've since rewired system C with MSF to serial dsr and
> pps to serial dcd, restarted and ntpq shows
> SHM(0)/MSFa and PPS(0) and after a short while get +SHM(0)
> then oPPS(0) with system having drifted > 10ms whilst
> rewiring and restarting but now back at < 1ms.
> So does pps really need a refclock and/or does pps via
> parallel work ok or not on NetBSD-5?
> Tomorrow I'll rewire gps that just about works ok out of
> bedroom window and give that a try on system A, NetBSD-5,
> with both serial and parallel.

Local TV = no signal so missed film I'd intended watching

so instead:

GPS + nmea driver + pps0 => tty0 ok
then after relinking to pps0 => lpt0 that's also ok.

only difference between that and non working setup is lack
of refclock for timecode and using one of servers on lan
set as preferred.

I'd intended just running ttl => lpt for pps but looks like
I'll also need rs232 with timecode signal.



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