Re: [avr-chat] Endless loop in AVR?

[Bob Paddock]

On Sat, 28 Jul 2007 08:24:35 -0400, Wojtek Dabrowski <address@hidden>  
wrote:


> Actually, no, I haven't touched microcontrollers before. I'm just used
> to +5V meaning that there is a signal, and ground meaning there is no
> signal

Many things in the world of Micros are active 'low'.

> Thanks for the help, I'll try those things now - I hope this depleted my
> repertiore of noob-questions for now :)

A tip for you:  Don't think of signals as being +5 or Ground nor
think of them of being high or low.  Think of them as being
Active/Asserted, or Inactive/Deasserted.  In the long run
it makes porting code between different hardware architectures
much less painful.  You can then write code that says
things like "AlarmLED_ASSERTED()" and you know that the LED
is on.  Where if you say "AlarmLED_HIGH()" you don't
really know what that means without intimate knowledge
of the hardware, and goes down hill fast if the next
revision of the hardware inverts something.


Here is a simple example of a button that
lights up a LED, without ever directly using
the concept of +5/High or Ground/Low in the main line code:

File hardware.h, that contains anything to do with the ports,
all such port data is centralized in this one file:

/* Menu Push Button Input: */
#define MenuPB_BIT                 (5)
#define MenuPB                     _BV(MenuPB_BIT)
#define MenuPB_ASSERT()            (BitClr(   PORTE, MenuPB_BIT ))
#define MenuPB_DEASSERT()          (BitSet(   PORTE, MenuPB_BIT ))
#define MenuPB_TOGGLE()            (BitToggle(PORTE, MenuPB_BIT ))
#define MenuPB_ASSERTED()          (!BitTest( PINE,  MenuPB_BIT ))
#define MenuPB_DEASSERTED()        ( BitTest( PINE,  MenuPB_BIT ))

/* LED Output: */
#define AlarmLED_BIT               (7)
#define AlarmLED                   _BV(AlarmLED_BIT)
#define AlarmLED_ASSERT()          (BitSet(   PORTB, AlarmLED_BIT ))
#define AlarmLED_DEASSERT()        (BitClr(   PORTB, AlarmLED_BIT ))
#define AlarmLED_TOGGLE()          (BitToggle(PORTB, AlarmLED_BIT ))
#define AlarmLED_ASSERTED()        ( BitTest( PINB,  AlarmLED_BIT ))
#define AlarmLED_DEASSERTED()      (!BitTest( PINB,  AlarmLED_BIT ))

File main.c:
#include <avr/io.h>
#include "hardware.h"
int main( void )
{
 DDRB = AlarmLED;

 for(;;)
  {
   if( MenuPB_ASSERTED() )
    {
     AlarmLED_ASSERT();
    }
   else
    {
     AlarmLED_DEASSERT();
    }
  }
}
/*
Code like that will be much clear to you if you ever
need to change the code a few years from now.
Consider how bad it would be if it said if( Button_LOW() ){ LED_LOW() }
and the schematic was long since lost...

See "Bit-level operations" in Bitops.How at  
http://c.snippets.org/browser.php
to see what BitSet()/BitClr() et.al do.
*/

There are other ways to do it as there always are, I've just found
that is what works the best for me over the years.