Re: [Fwd: Modes, stack setup for "no-OS" ARM app]

[Toralf Lund <toralf at procaptura dot com>]

Nick Clifton wrote:

> Hi Toralf,
>
> > Another question is how choose the stack size for each mode. For 
> > maximum flexibility, I guess I should allow the user to control each 
> > of the stacks via symbols defined in the linker script or similar, 
> > but that way the start code perhaps get a bit too dependent on 
> > external symbols.
>
>
> The size and location of the stacks is going to be highly dependent 
> upon the memory layout anyway, and since this layout is going to 
> affect the linker script used you cannot really avoid this 
> inter-dependence.

Yes, that's a good point...

> As a general rule of thumb you should be able to have very small 
> stacks for the interrupt handlers and a small stack for the supervisor 
> mode.  The user stack is normally arranged to grow into free memory 
> from the opposite end of the allocation heap, but you knew that 
> already :-)

But of course...

> > I'm actually trying to write a crt0.S that is sufficiently general to 
> > be included in the newlib sources, so I don't want to make 
> > assumptions about the memory layout, or even require the code to be 
> > loaded in writeable memory. (And if I can assume at least ARMv4, I 
> > proably won't have to.)
>
>
>
> Have you seen the libgloss sources ?  These are part of the newlib 
> module in the sourceware CVS repository and they represent another 
> attempt at organising and standardising the creating of startup 
> files.  There is even an ARM sub-directory present with a crt0 source 
> file suitable for use with RedBoot.

Yeah, I know.

There is none that assumes a plain system, though - i.e. one that 
doesn't even have anything like RedBoot - which is what I want. Or 
*maybe* I should port RedBoot after all (I decided not to earlier on), 
but that's a different discussion entirely. newlib/libc/sys/arm/crt0.S 
is mostly fine, though, except for the stack issues discussed here ;-)

I also looked for startup files that would set up for multiple modes on 
other platforms, but didn't find anything good.

> Cheers
>  Nick