On Sat, 2005-03-05 at 23:51 -0500, Jason Graham wrote:
> To Roy,
> 
> I'm not sure I understand what you are trying to do. Your interrupt can
> >occur
> >while your program is doing anything, anywhere in the code.  You want to
> >respond to the interrupt and rather than return to where the interrupt
> >occurred
> >you want to jump to some other specific location in the program.  Yes?  
> >Why?
> 
> 
> You got it...something wrong with that? It's just the way it has ta be.

First off, with an attitude and response like that you're giving people
VERY little reason to give up there time for free to help you.

Second, to answer your question, yes, it's possible there IS something
wrong with that. If that's the sort of behaviour you want it SOUNDS like
either you are approaching the problem in a non conventional way (not
always a bad idea) or you shouldn't be using an interrupt to begin with.

Can you at least elaborate as you WHY this behaviour is "just the way it
has ta be"?

Now, to get back to things, you say you want the interrupt to "return"
to a specific point. That makes it sound to me that you DON'T want
normal "interrupt" behaviour, you want more like a vectored jump. This
is certainly possible, and even useful in some circumstances, but to
call it an "interrupt" will confuse people.

Are you using assembler? If so the solution is easy: simply don't do a
RETFIE, instead do a GOTO (or BRA depending on your MCU of choice) to
your label. Be aware that this sort of structure will do BAD stuff with
your stack, so you must be VERY careful about ANY returns in your code
(i.e. disabling interrupts completely when doing a call). I'd actually
recommend avoiding returns completely if possible, just to much of a
recipe for disaster.

If you are using a compiled language I'd say you're stuck: I can't think
of a way to get most compilers I've see to do what you want. About the
only thing I can think of is to have the ISR set a flag that the main
routine samples and branches if set. This sort of behaviour is "common",
but I don't know if it'll do what you want.

In the future in might be a good idea to be a little nicer to the people
you are asking help from.
 

-----------------------------
Herbert's PIC Stuff:
http://repatch.dyndns.org:8383/pic_stuff/

-- 
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist