Gilles Chanteperdrix wrote: > Philippe Gerum wrote: >> Gilles Chanteperdrix wrote: >>> Philippe Gerum wrote: >>>> Gilles Chanteperdrix wrote: >>>>> Hi, >>>>> >>>>> I run clocktest on a system here, not running NTP, using >>>>> CONFIG_GENERIC_CLOCKEVENT, with a systematic drift of 3us/s. How can >>>>> this happen? Does it come from the error due to the multiply and shift >>>>> used for tsc to/from ns conversions ? >>>>> >>>> - ipipe_request_tickdev() returning a timer freq we don't like? >>> Well, I would expect ipipe_request_tickdev() to return the same >>> frequency as the one used by Linux. >>> >> Yes it does. But this value is used by Xenomai code. > > It turns out that the frequency used to convert tsc to ns is the cpu > frequency (which is kind of a misnomer, since your emulated tsc on arm > does not run at cpu frequency),
Yes, that's bad. We have a timebase frequency that applies to our clock readings for calculating delays, and a timer frequency used to rescale those delays for programming timer shots. The CPU frequency has no relevance here. The fact that x86 once assumed CPU freq == TSC freq is an unfortunate legacy that goes down deep to the I-pipe as well. which is computed though it should have > the same value as the timer frequency but is suject to rounding errors. > -- Philippe. _______________________________________________ Xenomai-core mailing list Xenomai-core@gna.org https://mail.gna.org/listinfo/xenomai-core
