From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: <4C167FB8.2050803@domain.hid> Date: Mon, 14 Jun 2010 21:15:04 +0200 From: Gilles Chanteperdrix MIME-Version: 1.0 References: <4C1672ED.4080101@domain.hid> In-Reply-To: <4C1672ED.4080101@domain.hid> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Subject: Re: [Xenomai-help] rt_task_set_periodic List-Id: Help regarding installation and common use of Xenomai List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: ramoncostacastello@domain.hid Cc: xenomai@xenomai.org Ramon wrote: > Hi, > > I'm beginning to work with periodical task in xenomai. Currently I'm > using rt_task_set_periodic. > > The third parameter RTIME period allows to specify the period in clock > ticks (taken from : > http://www.xenomai.org/documentation/xenomai-2.5/html/api/group__task.html). > > I would like to know how can I get information from the clock tick > (which is the value? , can be changed ?) ? the API provides some functions to convert between ticks and durations in nanoseconds. If the timer runs in aperiodic mode, however, the duration of the tick is one nanosecond. If the timer runs in periodic mode, the tick duration is the period of the periodic timer. All this, of course, is documented in Xenomai API documentation. > > Why Is the minimum period I can use in user space ? (experimentally it > seems to be 0.1ms in my system) Depends on your system. Also depends on the load you are running. You can measure this with the "latency" test. > Working in kernel space this period is lower ? Probably, again, depends on your system. > > > When using the POSIX skin > int pthread_make_periodic_np ( pthread_t thread,struct > timespec * starttp,struct timespec * periodtp ) > the resolution is the same ? (performance will be the same ?) I guess you mean latency. Yes, the latency depends on your system, not really on the skin you are using. The various Xenomai skins rely on a the same common core. This is explained in the various documents which you will find on Xenomai web site. > > Is there any simple approach to develop a periodic task using the POSIX > commands (pthread_cond_timedwait > ?) ? The POSIX way to run periodic tasks is with the clock_nanosleep with absolute dates. Or to create a timer and run sigwait to wait for next period, but this will not work (yet) with Xenomai. -- Gilles.