On 2013-02-25, Miroslav Lichvar <mlich...@redhat.com> wrote: > On Mon, Feb 25, 2013 at 01:44:02PM +0100, Kasper Pedersen wrote: >> From the PPS arrives, and to the kernel timestamps it, is a very long time. >> I wrote this to measure it: >> http://n1.taur.dk/edgetest.c >> (you will need a linux machine, gcc, and kernel-headers to compile) > > Very interesting, thanks! For my machine it shows that the interrupt > latency is around 12 us. > > I'm wondering if the kernel module could have an option which would > enable a polling method to time stamp the PPS events.
When I ran a test many years ago I used a program to put out a rising pulse onto one of the printer port output pins, and then connected that to the parallel port nack pin. I timestamped the time just before I put out the pulse, and the time at which the interrupt occured and got roughtly 1 to 2 microseconds delay. Ie, the interrupt service was of the order of 1us. 12us seems really long. Now this might be a difference between the serial and parallel interrupts or a difference in the interrupt sevice routine, but 12us still seems a long time. > _______________________________________________ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
