[LinuxPPS] Ghost PPS assert when PPS disconnected

[Ivar-Kristian Waarum]

Hi peoples,

Any ghostbusters out there...?

I have more or less followed the instructions in the wiki and managed to get LinuxPPS working with on an armel board with a Novatel GPS. ntpq -p gives all good info, 'reach=377', the offset and jitter are in the order of microseconds and if I check system time vs. UTC time on the internet they are synchronized on the second. So far so good!

However, since I got it working I seem to have a 'ghost' PPS signal detected by the kernel. It is shown both in dmesg ('PPS event at ...'), by running ppstest /dev/pps0 and if I cat /sys/class/pps/pps0/assert. The problem is that this happens after the PPS is no longer connected, it even happens when the board is booted without any GPS/PPS connected ever.

ntpq -p tells me the PPS is there and is synced, the only thing really changed is the 'reach' value: oGPS_NMEA(0) .GPS. (The 'when' value exceeds the 'poll' value by far. 'reach'=0, 'offset'=0.008, 'jitter'=0.000). And if I check the system time vs. UTC time on the internet, it lags with a few seconds.

Does anyone have an idea why this is happening?

My setup:
Debian Linux 2.6.34 with LinuxPPS compiled into the kernel, not loadable.

autoserial.conf:
/dev/ttyS0 uart 16550A port 0x03f8 irq 3 baud_base 115200 spd_normal skip_test low_latency

/etc/udev/rules.d/09.pps.rules:
KERNEL=="ttyS0", SYMLINK+="gps0"
KERNEL=="pps0", OWNER="root", GROUP="tty", MODE="0660", SYMLINK+="gpspps0"
KERNEL=="ttyS0", RUN+="/bin/setserial -v /dev/%k low_latency"

ntp-4.2.6p3

I do not use ldattach or the sudo modprobe 8250 command.

Friendly yours,
Ivar-Kristian

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