On Tue, 2009-04-28 at 14:21 +0200, Gilles Chanteperdrix wrote: > Philippe Gerum wrote: > > On Tue, 2009-04-28 at 07:50 +0200, Gilles Chanteperdrix wrote: > >> Hi, > >> > >> currently, the situation is this: > >> - the timing core uses an approximate value of the cpu frequency (using > >> xnarch_llmulshft) to do conversions between tsc and ns; > >> - the APIC timer reprogrammation still uses imuldiv, that is a more > >> exact cpu frequency, coupled with an approximate APIC frequency > >> (obtained from ipipe_request_tickdev), to do the conversion between tsc > >> delays and APIC delays; > >> - the posix skin uses llimd to do conversions between timespec and > >> timeval structures and tsc values > >> - the posix and native skins in user-space still use llimd to do > >> conversions between ns and tsc (only if using tsc in user-space). > >> > >> These are causes of unprecisions, I think we should fix this, though it > >> is unlikely to be the cause of the high jitters observed by Vikesh with > >> 2.5-rc1. > >> > > > > Ack, we definitely should. Working on allowing userland to use > > llmulshift for timing computations for the native skin here, as a first > > step. For that purpose, xnsysinfo_t has just been extended to carry the > > pre-scaled values needed for llmulshft. I just don't want to have to > > issue a syscall for those conversions to take place. > > Actually, the pre-scaled values could be re-computed in user-space > without changing the ABI.
We don't care that much about changing the ABI between -rc1 and -rc2 actually, so it mostly depends whether we want to backport the fix to 2.4 regarding the tsc->ns conversion, since we do not have any nodiv implementation for the ns->tsc one there yet. -- Philippe. _______________________________________________ Xenomai-core mailing list Xenomaifirstname.lastname@example.org https://mail.gna.org/listinfo/xenomai-core