[LinuxPPS] Re2: some problems with linuxPPS + GPS system

[david]

> ----------------------------------------------------------------------
> 
> Message: 1
> Date: Tue, 9 Sep 2008 09:59:42 -0700
> From: "Hal V. Engel" <hvengel at astound.net>
> Subject: Re: [LinuxPPS] some problems with linuxPPS + GPS system
> To: linuxpps at ml.enneenne.com
> Message-ID: <200809090959.42752.hvengel at astound.net>
> Content-Type: text/plain; charset="iso-8859-1"
> 
> On Tuesday 09 September 2008 02:42:56 am david wrote:
>> Dear all,
>>
>> I try to install on a pc with VIA processor a ntp system with a GP18LVC
>> garmin GPS.
>>
>> I use debian and recompile the kernel with 2.6.26 kernel and the diff
>> file ntp-pps-2.6.26.diff
>>
>> I follow the wiki but I had problem to get pps information.
>>
>> I found this difference with the wiki :
>>
>> 1) I need to load ktimer to have an answer at the command : tree
>> /sys/class/pps
> 
> If your pps device is working you should not need to do this.  The ktimer 
> module is to create a fake pps signal for testing.
> 
>> 2) the result show device missing field
>>
>> /sys/class/pps
>>
>> |-- pps0
>> |
>> |   |-- assert
>> |   |-- clear
>> |   |-- dev
>> |   |-- echo
>> |   |-- mode
>> |   |-- name
>> |   |-- path
>> |   |-- power
>> |   |   `-- wakeup
>> |   |-- subsystem -> ../../pps
>> |
>> |   `-- uevent
>>
>> `-- pps1
>>
>>      |-- assert
>>      |-- clear
>>      |-- dev
>>      |-- echo
>>      |-- mode
>>      |-- name
>>      |-- path
>>      |-- power
>>      |   `-- wakeup
>>      |-- subsystem -> ../../pps
>>
>>      `-- uevent
>>
>> 6 directories, 18 files
>>
>> 3) ./ppsfind /dev/ttyS0 give :
>>
>> pps0: name=serial0 path=/dev/ttyS0
>>
>> In the wiki this is pps1 (is it important ?)
> 
> No.
> 
>> 4) I patch ntpd with the file nmea.patch and when I try to get ntpq -p
>> information, I always had NMEA and not PPS like this :
>>
>> /usr/src/ntp-4.2.2p4/ntpq/ntpq -pn
>>       remote           refid      st t when poll reach   delay   offset
>>   jitter
>> ===========================================================================
>> === *127.127.20.0    .GPS.            0 l   18   16  377    0.000   10.107
>> 3.417
> 
> First you need to confirm that your pps signal is actaully working.   Have you 
> tried?

Yes it seems to work

> 
>  ppstest /dev/pps0

trying PPS source "/dev/pps0"
found PPS source "/dev/pps0"
ok, found 1 source(s), now start fetching data...
source 0 - assert 1221037543.828813020, sequence: 88131 - clear 
1221037543.028815792, sequence: 88130
source 0 - assert 1221037543.828813020, sequence: 88131 - clear 
1221037544.028833694, sequence: 88131
source 0 - assert 1221037544.828845730, sequence: 88132 - clear 
1221037544.028833694, sequence: 88131
source 0 - assert 1221037544.828845730, sequence: 88132 - clear 
1221037545.028867802, sequence: 88132
source 0 - assert 1221037545.828853296, sequence: 88133 - clear 
1221037545.028867802, sequence: 88132
source 0 - assert 1221037545.828853296, sequence: 88133 - clear 
1221037546.028870339, sequence: 88133


Can you explain the difference between pps0 and pps1 ?

sonde2:/usr/src/linux/Documentation/pps# ./ppstest /dev/pps1
trying PPS source "/dev/pps1"
found PPS source "/dev/pps1"
ok, found 1 source(s), now start fetching data...
source 0 - assert 1221037584.290399089, sequence: 88293 - clear 
0.000000000, sequence: 0
source 0 - assert 1221037585.290096541, sequence: 88294 - clear 
0.000000000, sequence: 0
source 0 - assert 1221037586.289778347, sequence: 88295 - clear 
0.000000000, sequence: 0
source 0 - assert 1221037587.289464624, sequence: 88296 - clear 
0.000000000, sequence: 0
source 0 - assert 1221037588.289143358, sequence: 88297 - clear 
0.000000000, sequence: 0



> 
> If so what do you get?  For this to work you will need to have ntpd stopped 
> and you will need to have 
> 
>  ppsldisc /dev/ttyS<what ever device you are using>
> 

ps afx show :

  1591 ?        Ss     0:03  \_ sshd: root at pts/0
  1595 pts/0    Rs     0:00  |   \_ -bash
  1640 pts/0    S      0:00  |       \_ ./ppsldisc /dev/ttyS0


> running.  The above (IE. ppsldisc...) also needs to be running when you start 
> ntpd.  There was an earlier thread here that started around Aug. 5 about this 
> titled gps_nmea error that you might want to have a look at.  This thread has 
> lots of details on what to expect from ppstest and lots of other info for the 
> refclock driver and GPS you are using.

Ok, I answer to this and I'll go to read it

> 
> If you are not getting the correct results for ppstest then we can help you 
> get that working.  Once that is working the rest is fairly easy.

this is the reason why I'm afraid !

> 
>> 5) my ntp.conf is :
>>
>> # /etc/ntp.conf, configuration for ntpd
>>
>> driftfile /var/lib/ntp/ntp.drift
>> statsdir /var/log/ntpstats/
>> logfile /var/log/ntpd.log
>>
>> statistics loopstats peerstats clockstats
>> filegen loopstats file loopstats type day enable
>> filegen peerstats file peerstats type day enable
>> filegen clockstats file clockstats type day enable
>>
>> logconfig = +syncall +clockall +sysall +peerall
>> statistics loopstats peerstats clockstats
>>
>> # LinuxPPS: GPS + PPS
>> server 127.127.20.0 prefer minpoll 4
>> fudge 127.127.20.0 flag3 1 flag2 0 time1 0.0
>>
>> # By default, exchange time with everybody, but don't allow configuration.
>> # See /usr/share/doc/ntp-doc/html/accopt.html for details.
>> restrict -4 default kod notrap nomodify nopeer noquery
>> restrict -6 default kod notrap nomodify nopeer noquery
>>
>> # Local users may interrogate the ntp server more closely.
>> restrict 127.0.0.1
>> #restrict ::1
>>
>>
>> I don't understand why I don't had the PPS information in ntpd
>>
>> I try to long PPS pulse to 200ms (I read something about problems on
>> web) without success.
> 
> The PPS pulse only needs to be longer than the clock tick interval for your 
> kernel.  So if you have this set to 100 ticks/second the pulse needs to be at 
> least 10 milliseconds or longer.  So pulse length is only really a concern for 
> devices with very short PPS pulse lengths (some are only a few milliseconds) 
> which is not an issue with your GPS.  Having a longer than needed pulse is not 
> an issue.
> 
> Hal
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