
Time to Measure the Pi (2016) [pdf] - fanf2
http://crin.eng.uts.edu.au/~darryl/Publications/Pi-hat_current.pdf
======
notanote
I’ve run a Pi 3 as a PPS clocksource. I used a netbooted aarch64 buildroot on
ramdisk, experimenting with rt-linux as well.

I saw similar performance, including those occasional spikes. I found that the
flood of interrupts caused by the usb chip - they are handled in the driver
rather than on chip - were detrimental to accuracy. Temperature variations
were another source of inaccuracy. I didn’t figure out how to connect an rtc
together with the gps hat.

I might try again on a Pi 4, I think it’s possible to power off the usb chip
without losing ethernet as it does on a Pi 3.

~~~
pmembrey
My Raspberry Pi 4 arrived today, so I'll be setting up some similar
experiments to see how it performs.

Would love to hear more about the issues you found with the USB chipset
though!

