On Thu, 2006-08-17 at 15:27 +0200, Jan Kiszka wrote: > Hi, > > the conflict between skins preferring aperiodic timing vs. skin > requiring periodic mode popped up once again on xenomai-help. One way > out of this, likely THE way, is to map such tick-driven skins on a > periodic timer over aperiodic mode (and drop periodic low-level support > completely at the same time). > > Let's start some discussion how this can be done, specifically as Gilles > and I are already turning the xntimer subsystem upside down (almost). If > we want co-existence of high-res timing of, say, the posix skin while > the vxworks skin runs over a tick-timer, we need some kind of "context" > for timing related functions. > > Simple example: xnpod_suspend_thread() expects a timeout as "xnticks", > i.e. either in nanoseconds or in ticks of the underlying periodic timer. > This depends on the global timer mode of the pod, and that's a no-go for > concurrent modes as sketched above. Rather, the thread should encode > which kind of timing mode to use, even better the threads timers. > > We currently dispatch xntimer_start globally to the different timer > subsystems (if periodic mode is enabled). What about deriving the start > function from the timer itself in the future? If a timer was created as > aperiodic, things happen as usual in aperiodic mode, and the timeout are > interpreted as nanoseconds. If the timer is periodic, we interpret the > timeout in ticks and map them on a second-level timing subsystem > (probably a wheel) that itself is driven by a single periodic timer in > the first-level system (just like the host tick). > > Am I heading in the right direction? Is it feasible? Any other ideas?
I like this idea; it's simple and elegant, having only a low impact on the existing interfaces. The two-level timer handling moving the BSD wheel on top of the aperiodic shot is definitely a clean approach, which adds no overhead to the existing periodic timer management. This would also allow to get rid of the specific Adeos support for periodic hw management. -- Philippe. _______________________________________________ Xenomai-core mailing list Xenomai-core@gna.org https://mail.gna.org/listinfo/xenomai-core
