Re: [avr-gcc-list] stumped by my ATmega48 (again)

[David Kelly]

On Oct 4, 2007, at 11:25 PM, address@hidden wrote:

> Hi all,
>
> I thought I was getting the hang of this Atmel programming, but after
> dusting things off a bit, I'm stumped again.  I have a demo program
> from Matthew MacClary at Oregon State that toggles all output pins
> every three seconds.  Pin 15 is hooked up to an LED on my breadboard,
> and when I install his prebuilt .hex file, the LED lights right up and
> does its thing.
>
> But when I build the same source and then install my hex file, the LED
> never lights up.
>
> To try to isolate the problem, I reduced the main program to just  
> this:
>
>         DDRB = 0xff;
>         DDRC = 0x7f; /* PORTC has only 7 pins */
>         DDRD = 0xff;
>
>         PORTB = 0xff;
>         PORTC = 0x7f;
>         PORTD = 0xff;
>         return 0;               /* PATCH for testing!  */
>
> I believe this should set all output pins high.  But again, when I
> build and install this, nothing; the LED doesn't light up.  Then I
> tried setting all ports to 0x00, but that didn't work either.

When you return the CPU goes thru a crash reset, or something like  
that, I haven't traced the code.

Do something like this:

        ...
        PORTB = 0xff;
        PORTC = 0x7f;
        PORTD = 0xff;
        for( ;; )
                ;
        return 0

Then again we've discussed the removal of empty loops to death. Make  
sure the compiler doesn't optimize out that empty loop. Possibly it  
recognizes it as infinite and leaves it alone.


--
David Kelly N4HHE, address@hidden
========================================================================
Whom computers would destroy, they must first drive mad.