Hi,
I have a raspberry pi with a gps connected to it.
It runs linux kernel 3.18.5+ and ntp version 1:4.2.6.p5+dfsg-2.
When I use my own rpi_gpio_ntp which is a userspace program, I get
something like:
remote refid st t when poll reach delay offset jitter
==============================================================================
*127.127.28.1 .PPS. 0 l 8 16 377 0.000 -0.010 0.008
*127.127.28.1 .PPS. 0 l 11 16 377 0.000 0.005 0.012
*127.127.28.1 .PPS. 0 l 12 16 377 0.000 0.005 0.012
*127.127.28.1 .PPS. 0 l 1 16 377 0.000 0.001 0.011
(I omitted the peers)
So the jitter is around 8us. Not bad for userspace.
Linux has this PPS interface for a while so now that it is easy
configurable in config.txt on the rpi, I thought I give that a try. The
strange thing now is that using that I get very bad jitter. So bad that
ntp discards it as a false ticker!
remote refid st t when poll reach delay offset jitter
==============================================================================
x127.127.22.1 .PPS. 0 l 2 16 377 0.000 0.161 0.001
x127.127.22.1 .PPS. 0 l 7 16 377 0.000 0.148 0.006
x127.127.22.1 .PPS. 0 l 13 16 377 0.000 0.147 0.007
x127.127.22.1 .PPS. 0 l 2 16 377 0.000 0.146 0.006
This is odd: the pps interface should work way better due to lower
latency etc.
What could be going wrong here?
The one at the top (28.1) uses GPS and the one at the bottom uses a
combined Glonass/GPS receiver. Note that I also swapped tried using pps
with 28.1 and rpi_gpio_ntp on 22.1 and then 28.1 fails and 22.1 is fine.
Folkert van Heusden
--
Curious about the inner workings of your car? Then check O2OO: it'll
tell you all that there is to know about your car's engine!
http://www.vanheusden.com/O2OO/
----------------------------------------------------------------------
Phone: +31-6-41278122, PGP-key: 1F28D8AE, www.vanheusden.com
_______________________________________________
questions mailing list
[email protected]
http://lists.ntp.org/listinfo/questions
