Re: Simultaneous reading from two channels?

From: Tim Beamish <tbeamish_at_cs.ubc.ca> · Date: Mon, 15 Jul 2002 08:17:17 -0700 (PDT)

How about using a semaphore (or mutex...what's the difference anyway)?

Tim

On Sun, 14 Jul 2002, Nicolas Cottaris wrote:

> Hello comedi-list,
>
> Does anyone know if it possible to read data simultaneously (via a
> single non-interruptible command)
> from two analog channels, instead of sequentially reading from one then
> the other?
>
> In my implementation a low priority RTAI task does the reading (among
> other things)
> while a higher priority RTAI task is controlling a different device (not
> related to comedi).
> The situation is that sometimes the higher priority task will be
> scheduled right between the
> two successive reading operations and therefore the two samples are not
> simultaneous but
> can differ by as much as 500 microseconds (of course this depends on the
> computational load of
> the higher priority RTAI task).
>
> Is there any comedi command that can do two successive reads as an
> atomic operation, i.e. non-interruptible, operation?
> Making the reading task having the highest priority is not the solution,
> as the other task must be
> scheduled always on time.  Like I said before, I only need to make sure
> that I read from the two
> channels as simultaneously as possible.
>
> Any ideas would be appreciated.
>
> Thanks,
>
> Nicolas
>
>
>
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