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ultimate gps pps signal and ftdi
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ultimate gps pps signal and ftdi

by bilsch on Sun Jan 13, 2013 12:26 am

So,

I've been working on a low power ntp server synced off of GPS. Running off of a raspberry pi. Due to the simple serial ( uart is tx/rx only afaik... ) I'm using an ftdi chip since it breaks everything out nicely.

I have communications working between the pi and the gps for NMEA data and can track between 10-13 ( occasionally I get 14, nice :-> ) however I'm having problems with getting the pps signal to work properly.

I hooked up the pps output to the CTS of the ftdi and I can attach the pps fine:
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pi@raspberrypi ~ $ sudo ldattach -s 9600 PPS /dev/ttyUSB0


Logs:
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Jan 12 23:19:52 raspberrypi kernel: [36168.272319] pps_core: source usbserial0 got cdev (251:0)
Jan 12 23:19:52 raspberrypi kernel: [36168.336427] pps pps0: new PPS source usbserial0
Jan 12 23:19:52 raspberrypi kernel: [36168.391261] pps pps0: source "/dev/ttyUSB0" added


However I'm don't get anything back from ppstest
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pi@raspberrypi ~/gits/pps-tools $ sudo ./ppstest /dev/pps0
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)
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)
time_pps_fetch() error -1 (Connection timed out)
time_pps_fetch() error -1 (Connection timed out)
time_pps_fetch() error -1 (Connection timed out)


From /var/log/syslog:
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Jan 12 23:21:27 raspberrypi kernel: [36262.468102] pps pps0: time format unspecified (11)
Jan 12 23:21:27 raspberrypi kernel: [36262.528005] pps pps0: PPS_FETCH
Jan 12 23:21:27 raspberrypi kernel: [36262.566098] pps pps0: timeout 3.000000000
Jan 12 23:21:30 raspberrypi kernel: [36265.608357] pps pps0: PPS_FETCH
Jan 12 23:21:30 raspberrypi kernel: [36265.646016] pps pps0: timeout 3.000000000
Jan 12 23:21:33 raspberrypi kernel: [36268.686861] pps pps0: PPS_FETCH
Jan 12 23:21:33 raspberrypi kernel: [36268.724769] pps pps0: timeout 3.000000000


Anyone know what I'm doing wrong here? I did have to compile the kernel myself to get the pps drivers. I've thought about getting the gpio input but ... well, this should be working ;)

bilsch
 
Posts: 14
Joined: Thu Oct 25, 2012 5:16 pm

Please be positive and constructive with your questions and comments.