Re: Re: [Rtlinuxgpl] Interrupt Prioritization

On Sun, Jan 01, 2006 at 05:22:22PM -0500, Calin A. Culianu wrote:
> 
> 
> On Sat, 31 Dec 2005, Der Herr Hofrat wrote:
> 
> >>
> >>I forget: Is this actually implemented in RTLinux/Free or RTLinux GPL
> >>Free?
> >>
> >no - the interrupt interception does not prioritize interrupts - I played
> >with it as it is fairly simple to implement but it really has close to 0
> >advantage as the you simply can run the hig priority ISR with disabled
> >interrupts, as it will preempt any other running ISR this de-facto has the
> >same effect as if you would prioritize interrupts. The overhead of
> >introducing interrupt priorities does not pay off if you keep your ISRs
> >short and shedule a "bottom-half" as a regular RT-thread.
> >
> >In what situation would you need it ?
> 
> Well, I am running a periodic task that I want to always run when it is 
> supposed to, and to never run late or be preempted in anyway -- but I also 
> have a realtime sound driver that feeds sounds to a soundcard to play them 
> (by writing to DMA buffers).  Anyway, I want the periodic task to always 
> preempt the sound driver ISR.  I suppose it is simple enough -- just run 
> the periodic task with interrupts disabled while making sure hard realtime 
> interrupts are always enabled when the sound driver ISR is running, right?

The design I recommend in RTLinux is to make the ISR very short and have it
pass the time consuming part to a thread. For example, the ISR can post
to a semphore and a thread can fill the sound driver buffer. 
Does that work for your application?

The problem with hardware priorities is that they are very machine dependent
and don't seem to add anything that this design does not give better.

What are you doing with the soundcard?
> 
> I see what you are saying about interrupt prioritization has 0 advantage 
> though -- I suppose what I want can be accomplished by the above, right?
> 
> -Calin
> 
> 
> _______________________________________________
> Rtl mailing list
> [email protected]
> http://hq.fsmlabs.com/mailman/listinfo/rtl
> http:/www.rtlinux-gpl.org/

-- 
---------------------------------------------------------
Victor Yodaiken 
Finite State Machine Labs: The RTLinux Company.
www.fsmlabs.com  www.rtlinux.com
1+ 505 838 9109

_______________________________________________
Rtl mailing list
[email protected]
http://hq.fsmlabs.com/mailman/listinfo/rtl
http:/www.rtlinux-gpl.org/