[ntp:questions] Two GPIO PPSes on Raspberry Pi

Richard B. Gilbert rgilbert88 at comcast.net
Fri Mar 1 03:26:17 UTC 2013

On 2/28/2013 6:03 PM, Chris Adams wrote:
> Once upon a time, Ralph Aichinger  <ralph at pangea.at> said:
>> 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)?
> Remember: a man with two clocks never knows what time it is.
> If they are the same, everything's great; if they are different, what do
> you do?

This looks so simple!!!  Is there a "catch" somewhere?

Try adding a third clock.  If NO TWO CLOCKS AGREE
you have a serious problem.

If you are relying on time from the Internet, that
may be your one of your problems!!!

I use a Global Positioning System (GPS) Timing Receiver
and get time good enough for most purposes.

It's specified +/- 50 nanoseconds.

If you need better, you can get it but you have some
studying to do and you had better have a "deep pocket"!
If your "deep Pocket" is not full of $1000 bills. . . .

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