[time-nuts] GPSD-Rb

Bob Camp lists at rtty.us
Thu Aug 23 18:00:58 EDT 2012


Hi

If you run a processor with a PLL on it - be very careful. The jitter they add can be significant.

Bob

On Aug 22, 2012, at 11:08 PM, Peter Bell <bell.peter at gmail.com> wrote:

> On Wed, Aug 22, 2012 at 11:27 PM, Chris Albertson <albertson.chris at gmail.com
>> wrote:
> 
>> 
>> It is very hard to write a divers in software.  You have to use assembly
>> language and you have to mmake sure that EVERY path in every branch is has
>> exactly the same number of clock cycles.   And then you have to be lucky
>> that you can work out an exact integer division.
>> 
> 
> It depends on what sort of processor you are using - that sort of approach
> used to be
> necessary when the low-cost MCUs were things like PICs that don't have
> especially sophisticated on-chip timers, but even cheap devices now have
> onchip
> timer/counters that have reload and capture registers. Many of them also
> have PLLs
> on the die that are intended for clock generation but can often be abused
> for other
> purposes :)
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