On Wed, Jun 17, 2020 at 09:09:22AM +0100, David J Taylor wrote: > I don't know what the path is on the RPi for the PPS interrupt but I would > expect it to be similar to that on the BBblack, so that latency graph is of > interest - thanks!
FWIW, there is a polling version of the GPIO PPS driver, which avoids the interrupt latency with a busy loop and which might be useful for measuring the latency. It will make the system clock more accurate, but it might have a negative impact on the accuracy of the NTP server as the PPS interrupt latency compensates the NIC interrupt latency (when the NIC driver is not polling). In my tests with a RPi 3B+ the RX timestamping error was about 20us larger than the TX error. The driver is here: https://github.com/mlichvar/pps-gpio-poll Getting it to work with the Raspbian kernel might be tricky. IIRC I didn't work for me the last time I tried. I prefer OpenWrt on these small computers. -- Miroslav Lichvar _______________________________________________ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
