[time-nuts] GPSDO with all-digital phase/time measurement?

Hal Murray hmurray at megapathdsl.net
Thu Feb 27 02:13:12 EST 2014


bob at evoria.net said:
> At least on the PIC I'm using, the CCP and timer interrupts don't seem to be
> synchronous with the PIC clock.  I could be mistaken. 

Unless you have a very strange architecture, it doesn't make sense for an 
interrupt to not be synchronous with the CPU clock.  You are in the middle of 
an add instruction, and now you want to start an interrupt.  What does that 
mean?

I expect there is the standard 2 FF synchronizer on all the input pins.  
Things like the counter/timers run on the CPU clock, taking their input after 
the synchronizer.  I don't remember seeing a data sheet that comes out and 
says that, but sometimes you can get some (strong?) hints with things like 
minimum pulse widths or max clock rate.


-- 
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