[LinuxPPS] ktimer works with the PL-2303 USB to serial converter, but the ppsldisc utility doesn't

[Ron Wright]

Hi there,

I was testing out LinuxPPS with the Prolific PL-2303 USB to serial converter
using a patched version of Linux Kernel 2.6.27 under Ubuntu 8.10 Intrepid,
and I loaded the ktimer module.  The time stamp showed up in the assert file
under /sys/class/pps/pps0 without any problem.  However, I tried the
ppsldisc utility, but all I see in both the assert and clear files in the
pps0 directory was "0.000000000#0":

fit at ubuntu-fitPC:/home/fit/ubuntu-intrepid-new/Documentation/pps$ cat
/sys/class/pps/pps0/{assert,clear}
0.000000000#0
0.000000000#0

I used the ppstest utilty that confirms the problem:

fit at ubuntu-fitPC:/home/fit/ubuntu-intrepid-new/Documentation/pps$ sudo
./ppstest /dev/pps0
[sudo] password for fit:
trying PPS source "/dev/pps0"
found PPS source "/dev/pps0"
ok, found 1 source(s), now start fetching data...
time_pps_fetch() error -1 (Connection timed out)
time_pps_fetch() error -1 (Connection timed out)
time_pps_fetch() error -1 (Connection timed out)
time_pps_fetch() error -1 (Connection timed out)
^C

By the way, the computer is a fit-PC Slim; it has a built-in serial port,
but it only uses the TX, RX, and GND lines.  The PL-2303 converter that I am
using instead uses at least the DCD, TX, RX, and GND lines that I need to
use, since the PPS signal is on the DCD line.  The GPS that I am using is a
Garmin GPS-18-LVC.  PPS itself is enabled and working, since I made a device
for the GPS comprising of one of two LEDs that confirms that the PPS signal
works.

The NMEA data does not come before the PPS signal; it comes after the
signal.  AFAIK, there is no setting on the GPS to make the NMEA data come
before the PPS signal, so this is why I need to use the clear file.  If
anyone can find possible solutions to the problem, I will greatly appreciate
it.

Regards,

Ron
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