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Re: Arm user mode


Andrew Lunn wrote:
> 
> On Fri, Apr 04, 2003 at 01:41:03PM +0200, Pierre Habraken wrote:
> > I discovered yesterday that Arm user mode has not been considered in
> > exception processing in hal/arm/arch/current/src/vectors.S.
> > Can someone tell me what has been the reason for that (apart the
> > fact that most of embedded applications do not need to run user mode
> > tasks) ?
> 
> That is the reason. Why make things more complex than they need to
> be. Why do you need user mode tasks?

I use the Evaluator7t board and the Gnu Arm tool chain for teaching
hardware and software architectures (at 1st level) to undergraduate
students. At some time in the cursus, students learn the basis of
context switching. They have to fill in a program which simulates a very
simple Unix-like (round robin preemptive) multi-tasking kernel. The
tasks managed by this small kernel run as user mode programs.


> > I added a few lines to vectors.S (see patch below) in order to take
> > in account the case where an exception occured while the processor
> > was running in user mode (this patch does not deal with either FIQ
> > or IRQ for the time being).
> 
> Minor point: You did the diff the wrong way around. Your patch takes
> code out, not putting it in. Its a simple mistake i commonly make!

I was aware of that (had to patch -R) but did not fix it as I didn't
know whether this patch makes sense (for people other than me).
Do you think I should send it to ecos-patches at once for getting more
advices before applying changes to FIQ and IRQ handling ?

Pierre
-- 
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Pierre HABRAKEN - mailto:Pierre dot Habraken at imag dot fr
Tél: 04 76 82 72 83 - Fax: 04 76 82 72 87
IMAG-LSR BP72 38402 SAINT MARTIN D'HERES Cedex
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