Is it a good idea to use a usb-serial adapter for PPS input? Yes, it is.

[O'Connor, Daniel]

> On 19 Aug 2019, at 17:09, O'Connor, Daniel <darius at dons.net.au> wrote:
> I am going to try this diff but buildkernel is going to take a while...

Was a lot faster cross building, so I installed it this morning:
[gps 1:56] ~ >uname -a
FreeBSD gps 13.0-CURRENT FreeBSD 13.0-CURRENT #1 41a4c010326-c262109(master)-dirty: Tue Aug 20 11:04:57 ACST 2019     darius at midget.dons.net.au:/usr/obj/arm-src/arm.armv7/sys/GENERIC  arm

[gps 1:57] ~ >dmesg|grep pps
am335x_dmtpps0: <AM335x PPS-Capture DMTimer4> mem 0x48044000-0x480443ff irq 30 on simplebus0
[gps 1:58] ~ >ll /dev/pps0 /dev/dmtpps
crw-rw----  1 root  ntpd   0x41 20 Aug 01:09 /dev/dmtpps
lrwxr-xr-x  1 root  wheel     6 20 Aug 01:09 /dev/pps0 -> dmtpps

[gps 1:58] ~ >cat /etc/ntp.conf
server 10.0.2.1 iburst prefer

server 127.127.22.0 minpoll 4 maxpoll 4
fudge  127.127.22.0 refid PPS

[gps 1:59] ~ >ntpq -nc pe
     remote           refid      st t when poll reach   delay   offset  jitter
==============================================================================
*10.0.2.1        214.52.129.40    3 u   64   64   37    0.349   -0.631   0.299
o127.127.22.0    .PPS.            0 l   13   16  377    0.000    1.000   0.106

It certainly seems happier with the PPS than it was before.

Next up would be to use the NMEA coming from the GPS engine for time instead of using the LAN host so it's self contained.

--
Daniel O'Connor
"The nice thing about standards is that there
are so many of them to choose from."
 -- Andrew Tanenbaum