Adjusting the drift is done in the function adjFreq in dep/sys.c. I tried the solutions of the links I looked at but setting the drift in the way they do it somehow doesn't work for my cards. I believe this might be because I don't calculate the drift correction correctly.
Does anyone know in what unit (like pps or ns/s) the parameter adj of the function adjFreq is?
thanks for your help
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The ptpClock->observedDrift (what is calculated by the servo and passed to adjFreq) is ppb (ns/s), i.e. drift 3500 = 3500 ppb = 3.5ppm = 3.5us/s frequency offset.
This value eventually converted and passed to the adjtimex syscall (freq), is scaled ppm, with the base being 2^16, i.e. frequency offset of 65536 = 1ppm. So observedDrift is multiplied by 65536 and divided by 1000.
You need to remember that the observedDrivft value is clamped (kept within bounds) to the kernel frequency offset limit, that is +/-512ppm.
Hope this helps.
If you would like to refer to this comment somewhere else in this project, copy and paste the following link:
Hello,
I am trying to add hardware timestamping for a network card to ptpd. I looked at this https://sourceforge.net/projects/ptpd/forums/forum/469207/topic/1852996 and this http://home.mit.bme.hu/~khazy/ptpd/. Setting and reading the clock of the card is working, so is reading timestamps. I am currently working on correcting the drift of the clock inside the card.
Adjusting the drift is done in the function adjFreq in dep/sys.c. I tried the solutions of the links I looked at but setting the drift in the way they do it somehow doesn't work for my cards. I believe this might be because I don't calculate the drift correction correctly.
Does anyone know in what unit (like pps or ns/s) the parameter adj of the function adjFreq is?
thanks for your help
The ptpClock->observedDrift (what is calculated by the servo and passed to adjFreq) is ppb (ns/s), i.e. drift 3500 = 3500 ppb = 3.5ppm = 3.5us/s frequency offset.
This value eventually converted and passed to the adjtimex syscall (freq), is scaled ppm, with the base being 2^16, i.e. frequency offset of 65536 = 1ppm. So observedDrift is multiplied by 65536 and divided by 1000.
You need to remember that the observedDrivft value is clamped (kept within bounds) to the kernel frequency offset limit, that is +/-512ppm.
Hope this helps.