RE: [ECOS] changing the stack ptr

[Gary Thomas <gthomas at redhat dot com>]

Chainging the stack with interrupts enabled is just asking for trouble.

How long of a routine is this?  Can you justify leaving interrupts off
for the time it runs?

Can't you get by with one fewer registers?

[questions asked just to play advocate]

On 26-Jul-2001 Dan Conti wrote:
> I'm working on the cirrus part.
> 
> I have a piece of code that needs to use all available registers. As
> such, i'm storing the sp off to a seperate location and reusing it as a
> normal data register. I have actually done this in the past with
> moderate success (on older kernels), but i'm having some problems now.
> 
> In the past, i used the sp to point into the middle of a data structure,
> the "upper" (as in >= sp) part of the structure being state data for the
> routine, and the "lower" (as in < sp) part of the structure was a small
> 1k stack, completely unrelated to the main thread stack. So basically i
> was able to use the sp register for my own purposes, but there was still
> a psuedo-stack that, if my routine was interrupted, could be used to
> store data on.
> 
> Using this same code on current cvs kernels i get the following
> exception:
> 
> ASSERT FAIL: <3>sched.cxx           [ 170] static void
> Cyg_Scheduler::unlock_inner()
>                 Bad next thread
> 
> I set a break in cyg_assert_fail(), and it appears that the entire stack
> is hosed.
> 
> Any thoughts?
> 
> -Dan
> 
> --
> Dan Conti             e danc@iobjects.com
> Software Engineer     p    (425) 289 0326