[EMAIL PROTECTED] (Hal Murray) writes:
>>>No. All you need is refclock_nmea (127.127.20.x) for a directly >>>connected NMEA device. Assuming that you're using a Linux kernel with >>>PPS-kit or a BSD kernel (or another kernel which directly supports PPS). >> >>OK, lets assume the kernel does NOT have the PPS support. Then what? >If you setup a NMEA refclock, it runs off the text strings >on the serial port. It works, it just doesn't keep as good >time as you normally get from PPS. Yes. I was wondering how to use the PPS output even if the kernel does not have pps support. There is the shm support. >How good depends on your GPS device. A lot of them have >a lot of jitter. The net ouput from a GArmin 18LVC into a Linux box, via my own interrupt routine, is about plus or minus 2usec ( that includes any jitter in the GPS pps signal, the clock reading jitter). I use my own parallel interrupt routine (based on the O'Reiley book by Alessandro Rubini and Jonathan Corbet "Linux Device Drivers"-- the short.c driver). which is read by an adapted shm driver. >You also get jitter from the OS (and serial port hardware). >There should be a simple recipe to minimize that. I haven't >seen one and several tries haven't produced anything that >I'd call good-enough. (When I run out of other things to >work on...) What is good enough? >-- >These are my opinions, not necessarily my employer's. I hate spam. _______________________________________________ questions mailing list [email protected] https://lists.ntp.org/mailman/listinfo/questions
