[time-nuts] F9T, was Re: Ublox F9P PPS output

[Bob kb8tq]

Hi

> On Feb 13, 2019, at 1:49 PM, Achim Gratz <Stromeko at nexgo.de> wrote:
> 
> Bob kb8tq writes:
>> It’s just like the other uBlox modules (and just like the F9T …) the external 
>> input is a once a second time stamper with an 8 ns resolution (just like the 
>> +/- 4 ns on the sawtooth ….).
> 
> A minor nit: If it works as the M8 series does (which is very likely),
> the timestamp facility gives you the last positive and the last negative
> going transitions w.r.t. the configured message rate, plus the count of
> positive going transistions.  This means you can get both higher
> timestamp rates by configuring a message rate of more than one per
> second (which does have some other implications, though) and can use
> (much) higher frequencies than just simply PPS (but get only the count +
> measurement of the last transitions).  Also, if the hardware doesn't use
> the second EXTINT pin for something else (like power management), there
> actually should be two of these timestamp inputs useable.
> 
>> One would *guess* they are using the same 
>> free running / TCXO clock for both the PPS out and the timestamp coming in. 
> 
> It's not confirmed in any documentation that I've found, but the above
> characteristic hints at the timestamp facility being some counters and
> registers in hardware, so the system clock is the only thing that could
> be used for this.  On a proper timing module with FTS firmware you could
> of course inject your own cleaned up clock to use as the timebase, plus
> you can use it to discipline an external frequency source.

The uBlox gizmos have two onboard clock sources. There’s a TCXO and an 
RTC oscillator. The RTC is at typical low power / low frequency gizmo. The
TCXO is the only thing in there that is good enough to generate the PPS or
to do the time stamps …..

Bob

> 
> Btw, if anybody is thinking about getting the ardusimple F9P-RTK module,
> somewhere in their forum it is mentioned that a bug on the current board
> revision has the PPS output at 0.7V instead of the documented 3.3V.
> 
> 
> Regards,
> Achim.
> -- 
> +<[Q+ Matrix-12 WAVE#46+305 Neuron microQkb Andromeda XTk Blofeld]>+
> 
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