Re: [avr-gcc-list] Using PORTB with variables, PORTB = var

[Ned Konz]

On Apr 22, 2006, at 9:20 AM, Matthew MacClary wrote:

>     Here is how I would implement your program. I apologize in advance
> since I don't have a board available to try the code on. I hope that
> the main ideas are apparent, even if I didn't squash all the bugs.

Here's a version of Matthew's code that will compile correctly (had  
to change the names of sleep() etc.);
using avr-gcc 4.1.0 it compiles to 142 bytes with the compilation  
options given below.

/*
avr-gcc -g -mmcu=atmega8 -fwhole-program -Os -o xx2c.elf xx2.c
avr-objdump -S xx2c.elf > xx2c.lst
*/

/* default 1MHz internal oscillator */
#define F_CPU 1000000

#include <avr/io.h>
#include <util/delay.h>

inline void
blink(volatile uint8_t * const port, uint8_t mask)
{
    *port = ~mask;              // LEDs on
    _delay_ms(500);             // milliseconds
    *port = 255;                // LEDs off
    _delay_ms(500);             // milliseconds
}

inline void
change(uint8_t * const var)
{
    *var <<= 1;
    if (! *var)
        *var = 1;
}

int
main()
{
    uint8_t led_mask = 1;

    DDRB = 255;                 // PORTB as outputs
    PORTB = 255;                // LEDs off

    while (1)
    {
        blink(&PORTB, led_mask);
        change(&led_mask);
    }
    return 0;
}

--
Ned Konz
MetaMagix embedded consulting
address@hidden