[time-nuts] ✘NEO-M8N vs. NEO-M8T

Bob kb8tq kb8tq at n1k.org
Mon May 21 15:56:25 EDT 2018


Backing up a bit ….

If this is all about a system that can quantize to 52 ns at best … your ADEV
plot shows everything *well* below that at all offsets you display. If you assume
a +/- 1 LSB sort of quantization, you are out to 104 ns. That’s 10X anything on
the plot. You would very much need to dig into just how the i/o structure on the
device actually handles asynchronous inputs to be sure of what it really is doing. 
There are a lot of “debounce / re-synch” sort of structures that get pasted into 
devices these days.


> On May 21, 2018, at 3:21 PM, Gary E. Miller <gem at rellim.com> wrote:
> Gregory!
> On Mon, 21 May 2018 19:06:17 +0000
> Gregory Maxwell <greg at xiph.org> wrote:
>> My best guess is that the magnitude of sawtooth error is just not
>> large enough to matter for typical applications of linux PPS.
> No need to guess.  I recently posted that the RasPi 3B granularity is
> 52 nano Seconds and the PPS offset reported by UBX-TP is double that!
> So, clearly it matters.
> I'll do more data logging to get harder numbers.
> ---------------------------------------------------------------------------
> Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703
> 	gem at rellim.com  Tel:+1 541 382 8588
> 	    Veritas liberabit vos. -- Quid est veritas?
>    "If you can’t measure it, you can’t improve it." - Lord Kelvin
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