[time-nuts] Deriving PPS from hockey-puck G-Mouse GPS receiver to lock an oscillator

[Mark Sims]

A long time ago, I did something very similar with an early release Magellan 5000 board  (and a couple of other models of GPS cards) that did not implement the 1PPS signal.  I think the best time sync that I ever got was around 1 mS (most boards were around 10 mS).  

True 1PPS signals are implemented and synchronized in hardware.  The NMEA messages are generated in software.  Due to the vagaries of things like software interrupt latencies,  serial port bit synchronization, etc I doubt that you could ever get better than 1 serial bit time of accuracy out of any board and 10-100 bit times is more likely.  At 4800 bits/sec the jitter/offset of even 1 bit time would be huge at best.  Perfectly OK for things like clock displays,  but totally inadequate for things like oscillator locking.
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