we recently have upgraded to a new industry PC from Vecow/Plugin and to Ubuntu 20.04 from 18.04. From the BIOS (build date BIOS ~17.02.2022) and the IO chip according to it is a SuperIO 8786: https://github.com/huchanghui123/ITE-SuperIO/blob/master/IT8786E-I_B_V0.2.pdf
This port seems to be mapped generic (ACPI/BIOS) as 16550A-compatible COM port PNP0501.
We have a PPS device connected to one (but tried all) serial/COM/RS232 port we have available (DCD Pin, we also connected GND). Which we attach to with ldattach pps /dev/ttyS0 and want to integrate with chrony again.
ldttach works and also ppstest. What happens is that after a short time (30-100 s), which seems to be rather random, it often fails to fetch the time stamps and times out and never recovers. But after deattaching and reattaching the ldisc it works again (for some time).
Instead of our PPS device we also tried a function generater at 1 Hz (pulse or duty cycle 50%, 1ms, 10ms, 100 and 200 ms). The Voltage level of our device which worked on the previous PC is 0 - ~3.7V. We set the function generator to operate within RS-232 at +/-3.7, 5, 6.6 and 10V (upper limit of our generator). Issue is the same.
We are on the HWE generic kernel btw (so 5.13). On the old PC it worked (even live via Ubuntu 20.04). We also tried an Ubuntu 22.04 live image (kernel 5.15) and Fedora 35 but it fails there too. Also on our second identical PC.
Anybody experienced something similar or has a clue how to debug it further? Especially to rule out a driver error (or any other HW error).
Thanks!
