Re: [openrisc] Trap exception revisited...

[Marko Mlinar <markom@opencores.org>]

> Question about trap exceptions. I'm confused about what
> they actually are. Is this a real exception, or is it
> simply an instruction? The l.trap definition says:
> 
>         l.trap  K
> 
>                 if SR[K]==1 then breakpoint-exception(K)
> 
> This would seem to indicate that trap isn't a real
> exception, and that the TE description should be
> removed from the documentation.
> 
> Gdb indicates a breakpoint like this:
> 
>         l.trap  0
> 
> But if this is correct, then what gdb is saying is that
> a breakpoint can only be executed in supervisor mode???
> (i.e. SR[0] = SR[SUPV]) That doesn't seem right to me.
> Most debugging will be done in user mode...
> 
> Also, the documentation in the 32/64 bit implementation
> section says a breakpoint exception will be thrown, but
> in the description it says trap exception.
> 
> Are a breakpoint exception and a trap exception the same
> thing?
> 
> Can someone describe to me the logic behind the trap
> instruction, and why we are using it for debugging?
> 
> The documentation seems internally inconsistent.
Huh, I was surpised too, when I saw this changed from previous
version. In previous version K was just breakpoint identifier.
Like you said gdb assumed K=0, since it has internal breakpoint
numbering. Damjan?

Marko
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