[time-nuts] GPS clock to RT-Linux for pulsar machine

Tom Van Baak tvb at leapsecond.com
Sat Jul 2 01:01:04 EDT 2005

> >And if you don't have a spare serial port you can
> >use another ADC channel to sample the raw bits
> >of the 4800 baud NMEA serial data ;-)
> >
> >This would also eliminate any problem with UART
> >or serial port driver latency...
> >
> >/tvb
> Yup, I was about to type that in the preceding message but thought it 
> was a bit over the top. I'd have to slow down NMEA serial to the ADC 
> sample rate too.

No need to slow down either one, I bet. With a
100 us ADC interval you're effectively sampling
a 4,800 bps signal at 10,000 bps. That is
oversample enough that you could reliably
reconstruct the 8N1 bits of the NMEA UTC
timestamp in software. More than one line of
code, to be sure; but a nice challenge. I also
think you'd earn a special prize for detecting
both the 1 PPS edge and decoding a NMEA
sentence using two spare ADC channels.


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