On Mon, Apr 04, 2011 at 10:02:41AM -0700, Bill Unruh wrote: > >Oh, my freetime project at the moment is to try and get the GPIO > >interrupts working as a kernel PPS module on the Alix board (hoping to > >get higher accuracy than using a serial port...) This coupled with an > >old Garmin 18 appears to allow for the possibility of a nice Stratum 1 > >time server for around the $100 ish mark... Could be cool! Will keep > >you informed how it goes...
Cool, I'd like to see how much will the jitter improve with GPIO and if it'll be better than the Soekris computer (http://phk.freebsd.dk/soekris/pps/). > You still get > usec level wander (ie it takes about 1-2 usec for the system to service the > interrupt and do the time stamping-- tested by having a program generate an > interrupt by putting out a signal on a parallel pin to the parallel interrupt > line (ACK) timing when that output went out and then having the interrupt > service routine timestamp the incoming interrupt.) but that is pretty good. A > Garmin 18 is not capable of better than that anyway. Isn't that a delay in the parallel port hw rather than a sw delay? I think with GPIO the interrupts go straight to the CPU, reducing the delay significantly. > For a cheaper version, get the sure GPS board. It is supposed to give about > 20ns timing on the PPS line, rather than garmin's 500-1000ns Someone reported on the ntp list that Garmin 18x is stable to 60 ns, not sure about the older version. -- Miroslav Lichvar --- To unsubscribe email chrony-users-requ...@chrony.tuxfamily.org with "unsubscribe" in the subject. For help email chrony-users-requ...@chrony.tuxfamily.org with "help" in the subject. Trouble? Email listmas...@chrony.tuxfamily.org.