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

[Bob Stewart]

Hi Hal,

I've reviewed this a bit and I used the wrong terminology.  Either Timer1 or Timer3 can use the T1CKI input as a clock.  Along with that, the CCP1 or CCP2 pin can be used to trigger a capture of the timer in use into the CCPR1 or CCPR2 register pair.  I had considered this as an interrupt function, but after looking at the manual, it's a matter of switchable dedicated hardware.  Sorry for the bad info.

Bob




>________________________________
> From: Hal Murray <hmurray at megapathdsl.net>
>To: Bob Stewart <bob at evoria.net>; Discussion of precise time and frequency measurement <time-nuts at febo.com> 
>Cc: hmurray at megapathdsl.net 
>Sent: Thursday, February 27, 2014 1:13 AM
>Subject: Re: [time-nuts] GPSDO with all-digital phase/time measurement?
> 
>
>
>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.
>
>
>-- 
>These are my opinions.  I hate spam.
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