> -----Original Message-----
> From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] On
Behalf
> Of piclist@xargs.com
> Sent: Thursday, February 23, 2006 6:58 PM
> To: Microcontroller discussion list - Public.
> Subject: RE: [PIC] 2 questions about 18f4550.
> 
> On Thu, 23 Feb 2006, William Killian wrote:
> 
> > There is no
> > compiler that can take a function and not generate the return or the
'as
> > if' version of return without guidance.
> 
> I've been using one for years that does it.  I've never had a function
> that mysteriously failed to return.  And I'm sure this compiler is not
> unique.

There is nothing mysterious.

Obviously I am not getting my point across.  I guess I'll have to
explain things more simply.

When a processor starts it always jumps to some address.  Jump not call.
Some are direct, some are indirect but a jump is made to that address.
It is not a call.  Branch on some processors is a jump and on others is
a call so I'll stick with the simplest jump and call terms.

Now there are two approaches we can use for the first executed code, one
is have a C function at that address, while the other is an assembly
language mainline code as opposed to a subroutine.

The C language is defined to only have subroutines called functions.  It
does not have non returning 'function' types.  Too bad; it is indeed a
weakness for embedded work and in some cases even for non-embedded.  

> 
> > Such a compiler would have to
> > be pretty good to identify a function that will never return but
know it
> > is not a mistake.
> 
> I don't see it as such a difficult problem.  If the last statement of
> the function branches to the beginning of the function, and there are
> no breaks/gotos in between that branch beyond the end of the outer
> loop, why would the function need a return?

There is no coding problem; the problem lies elsewhere possibly in
comprehension.  Since I intend to assume the best about you, it seems
you obviously are not getting the point.  It does not need a return.
You are indeed correct.  That is my entire point.

But, how does the compiler know that?  How does it know that it can
appropriately not generate any entrance and exit code?  Because you
wrote the function like that?  What if that is an error and you would
have wanted a warning about 'non reachable code' or 'function does not
exit'. Sure in a non multitasking word that is sometimes 'just one
function'.  In a multi-tasking world it is not.  Quite a few times I've
stumbled across applications - such as the slot machine I am working on
now - that has quite a few layers of functions called before you even
get into the one that has the endless loop.  This is a PIC list but the
issue is relevant more to non PIC chips in this case.







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