[ntp:questions] xGPS/oPPS

alex n alexvm22 at gmail.com
Sat Mar 10 19:55:19 UTC 2012

> >> Are both drivers using the same PPS signal?
> >
> >
> > Yes, it is so.
> >
> >
> >> If so, what do you hope to gain?
> >
> >
> > Why the same source (PPS)  may not be shared?
> You show it does. But why? It is the same source.
> Note that if this is not the same source-- ie is attached to  different
> interrupts ( parallel and serial ports for example) you will have
> interrupt contention. One of the interrupts will be seen by the computer
> as occuring first, and will be serviced first. Interrupts are turned off
> while the interrupt is serviced. Thus there is a 10-20us delay before
> the other interrupt is serviced. Ie, the two interrupts will not be timed
>  to  occur at
> the same time. They will have timestamps that differ by 10s of us.
> Now if it is the same interrupt that you are sending to two separate
> handlers, the question really is "why". There is no extra information
> that the two can give you.
As I understand ntp uses /dev/gpspps0 as pps source so all interrupts
things are placed into lower levels. For example I can run ppstest
/dev/pps0 at the same time with ntp and it works fine.


More information about the questions mailing list