Achim Gratz via devel writes: > I have been experimenting with determining the frequency offset via the > MONOTONIC_RAW clock. At the moment I've implemented that as a Perl > script although it should eventually go into some sort of pps-raw device > driver that timestamps the incoming PPS pulses.
After a long expedition through the Linux kernel sources it turns out that the lowest level timestamping facility in the kernel already provides both the raw and real timer counts via ktime_get_snapshot, which means that it is in principle unnecessary to make multiple transitions to and from user space to get that data. The PPS subsystem does actually work with dual timestamps as well (although only internally, these get not exposed via the PPS API or sysfs). However, that facility is unfortunately tied to CONFIG_NTP_PPS (PPS kernel consumer / hardpps) which most modern systems never define because it is incompatible with a tickless kernel (hardpps never made the transition to periodic timer triggered vs. tick triggered). It seems worthwile to a) try and disentangle dual timestamps from hardpps in the kernel config, then b) provide userspace access to dual timestamps. Does anybody have experience with Linux kernel development and can comment on how one would get started? The necessary changes would be neatly confined to the PPS subsystem I think. Regards, Achim. -- +<[Q+ Matrix-12 WAVE#46+305 Neuron microQkb Andromeda XTk Blofeld]>+ SD adaptations for KORG EX-800 and Poly-800MkII V0.9: http://Synth.Stromeko.net/Downloads.html#KorgSDada _______________________________________________ devel mailing list devel@ntpsec.org http://lists.ntpsec.org/mailman/listinfo/devel
