2012/3/11 unruh <un...@invalid.ca> > On 2012-03-10, alex n <alexv...@gmail.com> wrote: > >> > >> >> 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. > > If you are using /dev/pps0 for both sources, then as stated this is > pretty pointless. It is the same source. It cannot give different > answers. > You get no more information by reading it twice than by reading > it once. >
But why we need different answers? nmea+pps (127.127.20.0 flag1 1 flag3 1) and pps (127.127.22.0 flag3 1) drivers receive the same timestamp. ok. why it is wrong? Thanks, Alex. _______________________________________________ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions