Thanks Asat. I had setup a build environment a year or so ago. I will dust it off and try this out.
Here's my fixed GPS connected to the RT-AC68U router. The FT232RL USB-to-serial converter has a jumper to select either 3.3V TTL or 5V TTL.
If your PPS is working properly you will typically see a microseconds scale on the chart, not a milliseconds scale. A "u" is microseconds and "m" is milliseconds. Check /tmp/syslog.log for PPS issues related to NTPD.
set_ntp_ready()
{
/usr/bin/killall ntp
/bin/sleep 1
/usr/sbin/nvram set ntp_ready=$1
/usr/sbin/nvram unset ntp_server0
/usr/sbin/nvram unset ntp_server1
/usr/sbin/nvram unset ntp_server_tried
#/usr/sbin/nvram commit
}
set_ntp_ready 0
# create some folders used by ntpd, otherwise it don't work
/bin/mkdir -p /tmp/etc/ntp
/bin/mkdir -p /tmp/var/spool/ntp
# initialize ntpd
if [ ! -e /dev/ttyUSB0 ]; then
/sbin/lsmod | /bin/grep -e "ftdi_sio" > /dev/null 2>&1 || /sbin/modprobe ftdi_sio
/sbin/lsmod | /bin/grep -e "pps_core" > /dev/null 2>&1 || /sbin/ modprobe pps_core
/sbin/lsmod | /bin/grep -e "pps_ldisc" > /dev/null 2>&1 || /sbin/modprobe pps-ldisc
N=1
while [ $N -lt 30 ]; do
if [ -e /dev/ttyUSB0 ]; then
/jffs/bin/setserial /dev/ttyUSB0 low_latency
LDATTACH_CMD="/jffs/bin/ldattach pps /dev/ttyUSB0"
LDATTACH_PID=$(/bin/echo $(/bin/ps w | /bin/grep -i "$LDATTACH_CMD" | /bin/grep -v grep) | /usr/bin/cut -f1 -d' ')
[ -z "$LDATTACH_PID" ] && $LDATTACH_CMD
[ -e /dev/gps0 ] || ln -s /dev/ttyUSB0 /dev/gps0
[ -e /dev/gpspps0 ] || ln -s /dev/pps0 /dev/gpspps0
# block here while the router's clock is sync'd with a GPS time source
/usr/bin/logger -t $(/usr/bin/basename $0) "custom script attempting system clock synchronization [$$]"
/jffs/bin/ntpd -d -d -d -d -d -g -q -n -c /jffs/ntp/ntp.conf # set clock and quit
/usr/bin/logger -t $(/usr/bin/basename $0) "custom script completed system clock synchronization [$$]"
set_ntp_ready 1
break
else
let N++
/bin/sleep 1
fi
done
fi
# start ntpd as an unstoppable daemon and carry on
if [ "$(/usr/sbin/nvram get ntp_ready)" == "1" ]; then
/jffs/bin/ntpd -c /jffs/ntp/ntp.conf
fiThanks ASAT, I will give that a try - both reducing the baud rate and your script.
Mines is configured to send only NEMA sentence $GPZDA. Example:
$GPZDA,122235.00,13,01,2016,00,00*65...
# Generic NMEA GPS Receiver
# mode is 9600 baud + only $GxZDA for time messages
# /dev/gps0 for NEMA
# /dev/gpspps0 for PPS
# http://doc.ntp.org/4.2.8/drivers/driver20.html
server 127.127.20.0 mode 24 minpoll 4 prefer
fudge 127.127.20.0 flag1 1 # Enable PPS signal processing
fudge 127.127.20.0 flag2 0 # Capture the pulse on the rising edge
fudge 127.127.20.0 flag3 1 # Use the kernel discipline
fudge 127.127.20.0 flag4 1 # Obscures location in timecode
All honesty, it shouldn't be swinging about that much - but this is a PLL likely, so it'll drift a bit (HW).... what would be interesting is to chart it against CPU load and Temp... rrdtool is fun
I had to re-install my router and lost the NTP daemon settings: Now I cannot find the nice How To Guide. Is there a new URL for it?
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