[time-nuts] Can I get 1 millisecond accuracy with a USB GPS-18

Chris Albertson albertson.chris at gmail.com
Mon May 13 12:25:53 EDT 2013

On Mon, May 13, 2013 at 9:04 AM,  <lists at lazygranch.com> wrote:
> You might want to avoid the older Atom boards at this point. I think 28nm or 22nm is due soon.
> I have.an ARM board handy with serial and usb, but never set up NTS with a GPS. Is it just NEMA commands?

TO work well with NTP the borad needs a low latency PPS interrupt
handler.  THis means that you need both (1) the DCD line on the rs232
port tied to a CPU interrupt pin, with not much between the DCD and
the CPU pin and (2) The OS has a simple low latency handler.

Linux x86 has a good PPS handler.  I don't know about Linux ARM.  Also
I don't know how the interrupt hardware works on the ARM board.  But
if it is as described above it will work well enough.

You do need access to a hardware interrupt pin.

It might be NMEA or it might be some other serial protocol like TSIP.
The better timing type GPS receiver avoid NMEA because NMEA lacks soe
commands and timing data sentences.  NMEA was designed for boat and
ship navigation, not timing.

Chris Albertson
Redondo Beach, California

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