At 05:03 AM 27/09/2009, you wrote:
>William "Chops" Westfield wrote:
> > On Sep 26, 2009, at 12:39 PM, Quintin Beukes wrote:
> >
> >> The problem can be reproduced, however, by finish reading from the
> >> serial interface, then later one doing an exit(0). After doing that a
> >> few times all serial comms in the future are messed up.
> >
> > So you are undoubtably running into the differences between doing a
> > "real" reset and the partial re-start that happens (perhaps) when you
> > do exit(0).   A "real" reset will return most of the peripherals to a
> > default state, as well as restarting the program. A "software reset"
> > might ONLY return the program to its start address,
>
>Now, I do not remember what device this is, but executing the RESET
>instruction on a PIC18 (or one of the later PIC16 that has that
>instruction) is doing all register initializations that a hard
>reset does. What we do not know is if the exit(0) realy executes
>a real RESET instruction. If it could, depending on the device...
>--

MPSIM is a really good (and free) tool for figuring out what the compiler
and (in this case) the start-up code are up to.

MCC18 sets up the stack pointer, does the usual C initialization
such as clearing static variables, and then has a flow like this:

                         // initialization is complete at this point
loop:
__init();               // despite the name, by default this calls a 
null function.
   main();               // call the user main function
   goto loop;


As you can see, it behaves nothing like a RESET when you execute an
exit(0)-- nothing at all is re-initialized. To the extent exit() is
defined on a freestanding system (without a "host" or operating system),
it is supposed to call atexit-registered functions, flush buffers and close
streams, then return from main();

Calling exit() more than once is specifically indicated to cause undefined
behavior in the ANSI/ISO C99 standard.

I don't see any obvious and appropriate applications for exit() in a program
that runs on this kind of system.

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com



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