[time-nuts] GPSDO with a RaspberryPi

Javier Serrano javier.serrano.pareja at gmail.com
Fri Mar 1 08:28:24 EST 2013


On Fri, Mar 1, 2013 at 10:40 AM, Azelio Boriani
<azelio.boriani at screen.it> wrote:
> The metastability from the PPS latching the counter is indeed a problem:
> rarely do I see out of range numbers and have to filter them out.

You cannot filter them out. One time you will have bit 10 wrong and
you will be able to detect that, but what if it's bit 3, or bit 2, or
both? How can you know? What I proposed in a previous message solves
your problem: get the PPSReference signal into the Clk10MHz domain
before using it. This is the tried and proven way to deal with
metastability. I can provide a code snippet later if needed.

Cheers,

Javier


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