PPS over USB

[Hal Murray]

esr at thyrsus.com said:

>> fudge 127.127.22.1 refid PPSU time1 0.100700

> *Trailing* edge? That's disturbing. I thought previous observation had shown
> that the Adafruit hat reports rising edge.  If this so, whether we catch the
> rising or falling edge is variable based on more things than just the
> hardware type and life gets much more complcated.

The Adafruit HAT does the right thing.

We need to know the details of Dan's hardware setup.  I think the context of 
his fudge offset was with a non-HAT device.

You can flip the rising/falling aspect of the leading edge with an inverter.  
The standard RS-232 level shifters include an inverter.  If that's what's 
going on, I would have fudged flag2 to use the falling edge rather than 
fudging the time offset.

-- 
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