[ntp:questions] Timing issue with Linux and kernel PPS?

Uwe Klein uwe at klein-habertwedt.de
Sun Nov 18 15:20:47 UTC 2012


David Taylor wrote:
> On 18/11/2012 09:28, Uwe Klein wrote:
> 
>> David Taylor wrote:
>>
>>> Which part of the article or what keyword should I be looking for?
>>
>>
>> UpFront: haven't played around with the raspberry yet.
>>
>>
>> My understanding was that your /dev/pps0 entry appeared too late.
>> ( instantiated late by udev )
>>
>> is the module "pps-gpio" loaded during system startup ?
>>
>> lsmod ...
>>
>> other ref:
>>      https://github.com/davidk/adafruit-raspberrypi-linux-pps
>>      http://www.raspberrypi.org/phpBB3/viewtopic.php?f=9&t=1970
>>
>> uwe
> 
> 
> Thanks, uwe.  I've been using the pages you list as a guide.
> 
> On a working (with PPS pulses) system:
> 
> cat /etc/modules contains "pps-gpio"
> 
> lsmod shows:
> 
> pps_ldisc used by: 2
> pps_gpio used by: 1
> pps_core used by: 4 pps_gpio,pps_ldisc
> 
> 
> On a system with nothing connected to the PPS:
> 
> cat /etc/modules contains "pps-gpio"
> 
> lsmod shows:
> 
> pps_gpio used by: 0
> pps_core used by: 1 pps_gpio
> 
> 
> I'm unsure how to interpret the difference, or what pps_ldisc does.

what happens if you "insmod pps_ldisc" into the "not ready" system?

you may need a call to ldattach afterwards:
	http://net.its.hawaii.edu/network-performance/using-praecis/

"grep" your way through the udev scripts !?

uwe



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