roland Tollenaar wrote:
> Hi
>
> > Xenomai kernel implements the so-called "FIFO" scheduling policy, that
> > is, the task which runs at any time is the task with the highest
> > priority that has been ready for the longest time. Calling
> > rt_task_wait_period suspends the calling task, and let other tasks
> > run.
> >
> > If I understand correctly, what you want is to set some outputs at some
> You understand correctly.
>
> > precise deadline, I see two ways to do what you want:
> > * either the time when you compute the output has no importance, and the
> > only thing that matters is when you set the output, in which case you
> > can call rt_task_wait_period right before setting the outputs, your
> > task will do
> > compute next output
> > go to sleep
> > set output
> > compute next output
> > go to sleep
> > set output
> > etc...
> Actually this is exactly what I had in mind only it is important
> (discrete state space controller computations) that the input is also
> read at exact intervals. So maybe:
>
> compute next output k+1
> go to sleep
> read input for k+2 computations
> set output k+1
> compute next output k+2
> go to sleep
> read input for k+3 computations
> set output k+2
> > etc...
>
> > * or the time between reading input and setting output has to be as
> > fixed as possible, in which case what you will have to do is to
> > calibrate the WCET (worst case execution time) of the computations on
> > the machine you are running, setup rt_task_set_periodic so that your
> > task is woken up at (deadline - WCET), and in each loop, do the
> > computations, then busy wait until the deadline then set the
> > output. In order to busy wait, you may use rt_timer_tsc.
>
> Off hand I am not exactly sure why this second technique would give me
> a more fixed interval between reading input and writing output than
> the modified technique 1 I suggest above?
I supposed you had to read input k+1 after having set output k
--
Gilles Chanteperdrix.
_______________________________________________
Xenomai-help mailing list
[email protected]
https://mail.gna.org/listinfo/xenomai-help
