01_gpio

How to configure and use general purpose (digital) I/O pins.

File(s):

• arch/avr/tutorials/01_gpio/gpio.c

The LED shines while the push button is being pressed.

Compact C techniques are used to manipulate individual bits of a Peripheral Control Register. It is good programming practice to encapsulate these often used and error prone pieces of code in macros, as has been demonstrated in flashing_led : Microchip AVR Flashing LED example.

The following piece of code:

PORTB = PORTB | 0x01; // Set bit 0 of PORTB register to enable LED
PORTB = PORTB & 0xfe; // Clear bit 0 of PORTB to disable LED

can be compacted to:

PORTB |=  (1 << 0);     // Set bit 0 of PORTB register to enable LED
PORTB &= ~(1 << 0);     // Clear bit 0 of PORTB to disable LED

and better yet, be replaced with macros:

// General purpose bit manipulation macros
#define BIT_SET_HI(var, bit)    var |=  (1 << bit)
#define BIT_SET_LO(var, bit)    var &= ~(1 << bit)
 
// Define LED GPIO pin
#define GPIO_LED_REG_PORT       PORTB
#define GPIO_LED_BIT            0
 
// Define macros to turn LED on and off
#define LED_ON()                BIT_SET_HI(GPIO_LED_REG_PORT, GPIO_LED_BIT)
#define LED_OFF()               BIT_SET_LO(GPIO_LED_REG_PORT, GPIO_LED_BIT)
 
void example_fn(void)
{
    LED_ON();  // Enable LED
    LED_OFF(); // Disable LED
}

or best yet, use px_gpio.h : Microchip AVR GPIO driver. Here is an example:

#include "px_gpio.h"
 
// LED is on PORT B, pin 0, configured as an output, initally off
#define PX_GPIO_LED    PX_GPIO(B, 0, PX_GPIO_DIR_OUT, PX_GPIO_INIT_LO)
// Push Button is on PORT D, pin 7, configured as an input, pull-up enabled
#define PX_GPIO_PB     PX_GPIO(D, 7, PX_GPIO_DIR_IN, PX_GPIO_INIT_PULL_UP)
 
int main(void)
{
    // Initialise pins
    PX_GPIO_INIT(PX_GPIO_LED);
    PX_GPIO_INIT(PX_GPIO_PB);
 
    // Loop forever
    while(true)
    {
        // Is button being pressed?
        if(PX_GPIO_IN_IS_LO(PX_GPIO_PB))
        {
            // Enable LED
            PX_GPIO_OUT_SET_HI(PX_GPIO_LED);
        }
        else
        {
            // Disable LED
            PX_GPIO_OUT_SET_LO(PX_GPIO_LED);
        }
    }
}

Assuming Atmel Studio 7 is installed in it's default location, The peripheral registers and bit names are defined in:

C:\Program Files (x86)\Atmel\Studio\7.0\toolchain\avr8\avr8-gnu-toolchain\avr\include\avr\iom328p.h