Anthony DeRobertis wrote:
No, you don't. Four GPS satellites can tell you your position and the
current time.
They tell you the current time *at the GPS device*.
That's transmitted in plaintext over a relatively slow RS232 link,
interpreted by the operating system, then the NTP driver.. by the time
you get it it's way off.
PPS helps (enormously.. without it it's hard to get within 200ms) - but
even with that it's damned hard to get the GPS sync within 1.5
milliseconds of 'known' time, and the jitter is consistently 5ms or
more... that's just inevitable in a multi-tasking OS, even a relatively
idle one.
So in fact you don't know the 'real' time at all...
Tony
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