Quoting Hal Murray <hmur...@megapathdsl.net>:
PPS over USB will be off on average of 1/2 the polling interval. It's easy
to see if you have a decent place to stand. In some sense, it's not a big
deal. On the other, it's a systematic error so it's silly not to document
the fix, especially in a document that is mostly cut-n-paste.
Eric: Please plug your 701W into your Pi with HAT and collect some data.
Here's 7 days worth of data:
https://dan.drown.org/rpi/usb-vs-gpio-pps.html
The Rapsberry Pi 2's GPIO-PPS based local clock offsets at 0.1
percentile and 99.9 percentile were -3.61 microseconds and 4.13
microseconds.
The Raspberry Pi's USB-PPS based local clock offsets at 1 percentile
and 99 percentile were -582.97 microseconds and 539.08 microseconds.
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