[openrisc] Trap exception revisited...

[Chris Ziomkowski<chris@asics.ws>]

Guys,

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.

Thanks,

Chris
chris@asics.ws

P.S.

In order to proceed, I have ignored the definition for
now, and assumed a trap instruction always generates a
breakpoint exception. I have not implemented a new type
of trap exception.




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