Arduino -> AVR HOWTO

This is an (incomplete) guide to how to map from Arduino source code to avr-gcc source code. It's been written to map this this direction, but can be used to understand how to go the other direction as well.

Step 1: Setup project

Copy Makefile from some other project
- NB! Make sure DEVICE and SERIAL are correctly set
Copy the <MyProject.pde> file to main.cpp

Step 2: Edit main.cpp

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <avr/interrupt.h>
#include <avr/io.h>
#include <util/delay.h>

<insert .pde code here>

int main(void)
{
  cli();

  // set a2d reference to AVCC (5 volts)
  ADMUX &= ~(1<<REFS1);
	ADMUX |= (1<<REFS0);

	// set a2d prescale factor to 128
	// 16 MHz / 128 = 125 KHz, inside the desired 50-200 KHz range.
	// FIXME: this will not work properly for other clock speeds, and
	// this code should use F_CPU to determine the prescale factor.
  ADCSRA |= (1<<ADPS2)|(1<<ADPS1)|(1<<ADPS0)|
  // enable a2d conversions
  (1<<ADEN);

  setup();
  sei();

  while (1) {
    loop();
  }
		
  return 0;
}

Step 3: Port code away from Arduino

Arduino	AVR	Notes
byte	uint8_t
Serial.begin(<baud>)	uart_init(<baud>)
Serial.print*()	printf()
Serial.available()	getchar()	NB! blocking
pinMode(pin, INPUT)	DDRx &= ~_BV(bit);	// For I/O pins, convert pin to port+bit
pinMode(pin, OUTPUT)	DDRx \|= _BV(bit);
digitalWrite(pin, LOW)	PORTx &= ~_BV(bit);
digitalWrite(pin, HIGH)	PORTx \|= _BV(bit);
digitalRead(pin)	(PINx & _BV(bit)) >> bit;
delay(ms)	_delay_ms(ms)	max delay is 262.14 ms / F_CPU in MHz. (16Mhz -> 16 ms)
delayMicroseconds(us)	_delay_us(us)	max delay is 768 us / F_CPU in MHz. (16Mhz -> 48 us)
millis()		Must be rewritten or implemented using a timer

Misc. Notes

Address of I/O register: _SFR_IO_ADDR(PORTB)

(e.g. #define _SFR_IO_ADDR(sfr) (sfr - 0x20))

Read contents of I/O register: _SFR_IO8(register) // register = 00-3f

(e.g. #define PORTB _SFR_IO8(0x18))
      #define _SFR_IO8(io_addr) (io_addr + 0x20)

Arduino pins to AVR port+bit

digital
0	PORTD,0
1	PORTD,1
2	PORTD,2
3	PORTD,3
4	PORTD,4
5	PORTD,5
6	PORTD,6
7	PORTD,7
8	PORTB,0
9	PORTB,1
10	PORTB,2
11	PORTB,3
12	PORTB,4
13	PORTB,5
analog
0	PORTC,0
1	PORTC,1
2	PORTC,2
3	PORTC,3
4	PORTC,4
5	PORTC,5