Additional pps-gpio

[Hal Murray]

devel at ntpsec.org said:
> Well, maybe if I can think about a use of that measurement I might do it,
> but _creating_ a PPS from the rasPi and then measuring it externally with a
> TIC of sufficient resolution would be much more useful than teasing out this
> or that internal delay that is going to be highly variable anyway. 

I'm not sure what you mean by "_creating_ a PPS".

One approach would be to flap a modem control signal from userland.  You 
could grab the time before and after.  If you did it shortly after the second 
tick, you could measure the time between PPS and modem control.  That would 
give you a bracket on the offset of the system time.

There are comments in the kernel PPS documentation for an echo mode.  I 
didn't find any actual code.  But it seems like something in that area would 
be handy for measuring interrupt latency.


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