[ntp:questions] Two GPIO PPSes on Raspberry Pi

unruh unruh at invalid.ca
Thu Feb 28 17:48:03 UTC 2013


On 2013-02-28, Ralph Aichinger <ralph at pangea.at> wrote:
> Has anybody *two* GPIO PPS devices on different GPIO 
> pins on their Raspberry Pi? Would a setup like this
> enable the ntpd to check the devices against eachother
> (or probably more likely give an idea of interrupt
> handling capabilities)?

Yes, it is far more likely to do the latter. The interrupt processing is
serial, and thus the second interrupt would have to wait for the first
one to finish. That would give time errors of the order of 10-15us. 
I once tried to put two interrupt handlers in serial and found times
like that. 

>
> Or does more than one PPS device confuse ntpd?

It shuold not. 

>
> /ralph



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