Arduino/targets/arduino/wiring.c

/*
  wiring.c - Partial implementation of the Wiring API for the ATmega8.
  Part of Arduino - http://www.arduino.cc/

  Copyright (c) 2005-2006 David A. Mellis

  This library is free software; you can redistribute it and/or
  modify it under the terms of the GNU Lesser General Public
  License as published by the Free Software Foundation; either
  version 2.1 of the License, or (at your option) any later version.

  This library is distributed in the hope that it will be useful,
  but WITHOUT ANY WARRANTY; without even the implied warranty of
  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  Lesser General Public License for more details.

  You should have received a copy of the GNU Lesser General
  Public License along with this library; if not, write to the
  Free Software Foundation, Inc., 59 Temple Place, Suite 330,
  Boston, MA  02111-1307  USA

  $Id$
*/

#include <avr/io.h>
#include <avr/interrupt.h>
#include <avr/signal.h>
#include <avr/delay.h>
#include <stdio.h>
#include <stdarg.h>

#ifndef cbi
#define cbi(sfr, bit) (_SFR_BYTE(sfr) &= ~_BV(bit))
#endif
#ifndef sbi
#define sbi(sfr, bit) (_SFR_BYTE(sfr) |= _BV(bit))
#endif

#include "wiring.h"

// Define constants and variables for buffering incoming serial data.  We're
// using a ring buffer (I think), in which rx_buffer_head is the index of the
// location to which to write the next incoming character and rx_buffer_tail
// is the index of the location from which to read.
#define RX_BUFFER_SIZE 128

unsigned char rx_buffer[RX_BUFFER_SIZE];

int rx_buffer_head = 0;
int rx_buffer_tail = 0;

// The number of times timer 0 has overflowed since the program started.
// Must be volatile or gcc will optimize away some uses of it.
volatile unsigned long timer0_overflow_count;

// Get the hardware port of the given virtual pin number.  This comes from
// the pins_*.c file for the active board configuration.
int digitalPinToPort(int pin)
{
	return digital_pin_to_port[pin].port;
}

// Get the bit location within the hardware port of the given virtual pin.
// This comes from the pins_*.c file for the active board configuration.
int digitalPinToBit(int pin)
{
	return digital_pin_to_port[pin].bit;
}

int analogOutPinToTimer(int pin)
{
	return analog_out_pin_to_timer[pin];
}

int analogInPinToBit(int pin)
{
	return analog_in_pin_to_port[pin].bit;
}

void pinMode(int pin, int mode)
{
	if (digitalPinToPort(pin) != NOT_A_PIN) {
		if (mode == INPUT)
			cbi(_SFR_IO8(port_to_mode[digitalPinToPort(pin)]),
				digitalPinToBit(pin));
		else
			sbi(_SFR_IO8(port_to_mode[digitalPinToPort(pin)]),
				digitalPinToBit(pin));
	}
}

void digitalWrite(int pin, int val)
{
	if (digitalPinToPort(pin) != NOT_A_PIN) {
		// If the pin that support PWM output, we need to turn it off
		// before doing a digital write.

		if (analogOutPinToTimer(pin) == TIMER1A)
			cbi(TCCR1A, COM1A1);

		if (analogOutPinToTimer(pin) == TIMER1B)
			cbi(TCCR1A, COM1B1);
			
#if defined(__AVR_ATmega168__)
		if (analogOutPinToTimer(pin) == TIMER0A)
			cbi(TCCR0A, COM0A1);
			
		if (analogOutPinToTimer(pin) == TIMER0B)
			cbi(TCCR0A, COM0B1);

		if (analogOutPinToTimer(pin) == TIMER2A)
			cbi(TCCR2A, COM2A1);
			
		if (analogOutPinToTimer(pin) == TIMER2B)
			cbi(TCCR2A, COM2B1);
#else
		if (analogOutPinToTimer(pin) == TIMER2)
			cbi(TCCR2, COM21);
#endif

		if (val == LOW)
			cbi(_SFR_IO8(port_to_output[digitalPinToPort(pin)]),
				digitalPinToBit(pin));
		else
			sbi(_SFR_IO8(port_to_output[digitalPinToPort(pin)]),
				digitalPinToBit(pin));
	}
}

int digitalRead(int pin)
{
	if (digitalPinToPort(pin) != NOT_A_PIN) {
		// If the pin that support PWM output, we need to turn it off
		// before getting a digital reading.

		if (analogOutPinToTimer(pin) == TIMER1A)
			cbi(TCCR1A, COM1A1);

		if (analogOutPinToTimer(pin) == TIMER1B)
			cbi(TCCR1A, COM1B1);
			
#if defined(__AVR_ATmega168__)
		if (analogOutPinToTimer(pin) == TIMER0A)
			cbi(TCCR0A, COM0A1);
			
		if (analogOutPinToTimer(pin) == TIMER0B)
			cbi(TCCR0A, COM0B1);

		if (analogOutPinToTimer(pin) == TIMER2A)
			cbi(TCCR2A, COM2A1);
			
		if (analogOutPinToTimer(pin) == TIMER2B)
			cbi(TCCR2A, COM2B1);
#else
		if (analogOutPinToTimer(pin) == TIMER2)
			cbi(TCCR2, COM21);
#endif

		return (_SFR_IO8(port_to_input[digitalPinToPort(pin)]) >>
			digitalPinToBit(pin)) & 0x01;
	}
	
	return LOW;
}

int analogRead(int pin)
{
	unsigned int low, high, ch = analogInPinToBit(pin);

	// the low 4 bits of ADMUX select the ADC channel
	ADMUX = (ADMUX & (unsigned int) 0xf0) | (ch & (unsigned int) 0x0f);

	// without a delay, we seem to read from the wrong channel
	delay(1);

	// start the conversion
	sbi(ADCSRA, ADSC);

	// ADSC is cleared when the conversion finishes
	while (bit_is_set(ADCSRA, ADSC));

	// we have to read ADCL first; doing so locks both ADCL
	// and ADCH until ADCH is read.  reading ADCL second would
	// cause the results of each conversion to be discarded,
	// as ADCL and ADCH would be locked when it completed.
	low = ADCL;
	high = ADCH;

	// combine the two bytes
	return (high << 8) | low;
}

// Right now, PWM output only works on the pins with
// hardware support.  These are defined in the appropriate
// pins_*.c file.  For the rest of the pins, we default
// to digital output.
void analogWrite(int pin, int val)
{
	// We need to make sure the PWM output is enabled for those pins
	// that support it, as we turn it off when digitally reading or
	// writing with them.  Also, make sure the pin is in output mode
	// for consistenty with Wiring, which doesn't require a pinMode
	// call for the analog output pins.
	pinMode(pin, OUTPUT);
	
	if (analogOutPinToTimer(pin) == TIMER1A) {
		// connect pwm to pin on timer 1, channel A
		sbi(TCCR1A, COM1A1);
		// set pwm duty
		OCR1A = val;
	} else if (analogOutPinToTimer(pin) == TIMER1B) {
		// connect pwm to pin on timer 1, channel B
		sbi(TCCR1A, COM1B1);
		// set pwm duty
		OCR1B = val;
#if defined(__AVR_ATmega168__)
	} else if (analogOutPinToTimer(pin) == TIMER0A) {
		// connect pwm to pin on timer 0, channel A
		sbi(TCCR0A, COM0A1);
		// set pwm duty
		OCR0A = val;	
	} else if (analogOutPinToTimer(pin) == TIMER0B) {
		// connect pwm to pin on timer 0, channel B
		sbi(TCCR0A, COM0B1);
		// set pwm duty
		OCR0B = val;
	} else if (analogOutPinToTimer(pin) == TIMER2A) {
		// connect pwm to pin on timer 2, channel A
		sbi(TCCR2A, COM2A1);
		// set pwm duty
		OCR2A = val;	
	} else if (analogOutPinToTimer(pin) == TIMER2B) {
		// connect pwm to pin on timer 2, channel B
		sbi(TCCR2A, COM2B1);
		// set pwm duty
		OCR2B = val;
#else
	} else if (analogOutPinToTimer(pin) == TIMER2) {
		// connect pwm to pin on timer 2, channel B
		sbi(TCCR2, COM21);
		// set pwm duty
		OCR2 = val;
#endif
	} else if (val < 128)
		digitalWrite(pin, LOW);
	else
		digitalWrite(pin, HIGH);
}

void beginSerial(long baud)
{
#if defined(__AVR_ATmega168__)
	UBRR0H = ((F_CPU / 16 + baud / 2) / baud - 1) >> 8;
	UBRR0L = ((F_CPU / 16 + baud / 2) / baud - 1);
	
	// enable rx and tx
	sbi(UCSR0B, RXEN0);
	sbi(UCSR0B, TXEN0);
	
	// enable interrupt on complete reception of a byte
	sbi(UCSR0B, RXCIE0);
#else
	UBRRH = ((F_CPU / 16 + baud / 2) / baud - 1) >> 8;
	UBRRL = ((F_CPU / 16 + baud / 2) / baud - 1);
	
	// enable rx and tx
	sbi(UCSRB, RXEN);
	sbi(UCSRB, TXEN);
	
	// enable interrupt on complete reception of a byte
	sbi(UCSRB, RXCIE);
#endif
	
	// defaults to 8-bit, no parity, 1 stop bit
}

void serialWrite(unsigned char c)
{
#if defined(__AVR_ATmega168__)
	while (!(UCSR0A & (1 << UDRE0)))
		;

	UDR0 = c;
#else
	while (!(UCSRA & (1 << UDRE)))
		;

	UDR = c;
#endif
}

int serialAvailable()
{
	return (rx_buffer_head - rx_buffer_tail) % RX_BUFFER_SIZE;
}

int serialRead()
{
	// if the head isn't ahead of the tail, we don't have any characters
	if (rx_buffer_head == rx_buffer_tail) {
		return -1;
	} else {
		unsigned char c = rx_buffer[rx_buffer_tail];
		rx_buffer_tail = (rx_buffer_tail + 1) % RX_BUFFER_SIZE;
		return c;
	}
}

void serialFlush()
{
	// don't reverse this or there may be problems if the RX interrupt
	// occurs after reading the value of rx_buffer_head but before writing
	// the value to rx_buffer_tail; the previous value of rx_buffer_head
	// may be written to rx_buffer_tail, making it appear as if the buffer
	// were full, not empty.
	rx_buffer_head = rx_buffer_tail;
}

#if defined(__AVR_ATmega168__)
SIGNAL(SIG_USART_RECV)
#else
SIGNAL(SIG_UART_RECV)
#endif
{
#if defined(__AVR_ATmega168__)
	unsigned char c = UDR0;
#else
	unsigned char c = UDR;
#endif

	int i = (rx_buffer_head + 1) % RX_BUFFER_SIZE;

	// if we should be storing the received character into the location
	// just before the tail (meaning that the head would advance to the
	// current location of the tail), we're about to overflow the buffer
	// and so we don't write the character or advance the head.
	if (i != rx_buffer_tail) {
		rx_buffer[rx_buffer_head] = c;
		rx_buffer_head = i;
	}
}

void printMode(int mode)
{
	// do nothing, we only support serial printing, not lcd.
}

void printByte(unsigned char c)
{
	serialWrite(c);
}

void printNewline()
{
	printByte('\n');
}

void printString(char *s)
{
	while (*s)
		printByte(*s++);
}

void printIntegerInBase(unsigned long n, unsigned long base)
{ 
	unsigned char buf[8 * sizeof(long)]; // Assumes 8-bit chars. 
	unsigned long i = 0;

	if (n == 0) {
		printByte('0');
		return;
	} 

	while (n > 0) {
		buf[i++] = n % base;
		n /= base;
	}

	for (; i > 0; i--)
		printByte(buf[i - 1] < 10 ?
			'0' + buf[i - 1] :
			'A' + buf[i - 1] - 10);
}

void printInteger(long n)
{
	if (n < 0) {
		printByte('-');
		n = -n;
	}

	printIntegerInBase(n, 10);
}

void printHex(unsigned long n)
{
	printIntegerInBase(n, 16);
}

void printOctal(unsigned long n)
{
	printIntegerInBase(n, 8);
}

void printBinary(unsigned long n)
{
	printIntegerInBase(n, 2);
}

/* Including print() adds approximately 1500 bytes to the binary size,
 * so we replace it with the smaller and less-confusing printString(),
 * printInteger(), etc.
void print(const char *format, ...)
{
	char buf[256];
	va_list ap;
	
	va_start(ap, format);
	vsnprintf(buf, 256, format, ap);
	va_end(ap);
	
	printString(buf);
}
*/

SIGNAL(SIG_OVERFLOW0)
{
	timer0_overflow_count++;
}

unsigned long millis()
{
	// timer 0 increments every 64 cycles, and overflows when it reaches
	// 256.  we would calculate the total number of clock cycles, then
	// divide by the number of clock cycles per millisecond, but this
	// overflows too often.
	//return timer0_overflow_count * 64UL * 256UL / (F_CPU / 1000UL);
	
	// instead find 1/128th the number of clock cycles and divide by
	// 1/128th the number of clock cycles per millisecond
	return timer0_overflow_count * 64UL * 2UL / (F_CPU / 128000UL);
}

void delay(unsigned long ms)
{
	unsigned long start = millis();
	
	while (millis() - start < ms)
		;
}

/* Delay for the given number of microseconds.  Assumes a 16 MHz clock. 
 * Disables interrupts, which will disrupt the millis() function if used
 * too frequently. */
void delayMicroseconds(unsigned int us)
{
	// calling avrlib's delay_us() function with low values (e.g. 1 or
	// 2 microseconds) gives delays longer than desired.
	//delay_us(us);

	// for a one-microsecond delay, simply return.  the overhead
	// of the function call yields a delay of approximately 1 1/8 us.
	if (--us == 0)
		return;

	// the following loop takes a quarter of a microsecond (4 cycles)
	// per iteration, so execute it four times for each microsecond of
	// delay requested.
	us <<= 2;

	// account for the time taken in the preceeding commands.
	us -= 2;

	// disable interrupts, otherwise the timer 0 overflow interrupt that
	// tracks milliseconds will make us delay longer than we want.
	cli();

	// busy wait
	__asm__ __volatile__ (
		"1: sbiw %0,1" "\n\t" // 2 cycles
		"brne 1b" : "=w" (us) : "0" (us) // 2 cycles
	);

	// reenable interrupts.
	sei();
}

/*
unsigned long pulseIn(int pin, int state)
{
	unsigned long width = 0;

	while (digitalRead(pin) == !state)
		;
		
	while (digitalRead(pin) != !state)
		width++;
		
	return width * 17 / 2; // convert to microseconds
}
*/

/* Measures the length (in microseconds) of a pulse on the pin; state is HIGH
 * or LOW, the type of pulse to measure.  Works on pulses from 10 microseconds
 * to 3 minutes in length, but must be called at least N microseconds before
 * the start of the pulse. */
unsigned long pulseIn(int pin, int state)
{
	// cache the port and bit of the pin in order to speed up the
	// pulse width measuring loop and achieve finer resolution.  calling
	// digitalRead() instead yields much coarser resolution.
	int r = port_to_input[digitalPinToPort(pin)];
	int bit = digitalPinToBit(pin);
	int mask = 1 << bit;
	unsigned long width = 0;

	// compute the desired bit pattern for the port reading (e.g. set or
	// clear the bit corresponding to the pin being read).  the !!state
	// ensures that the function treats any non-zero value of state as HIGH.
	state = (!!state) << bit;

	// wait for the pulse to start
	while ((_SFR_IO8(r) & mask) != state)
		;
	
	// wait for the pulse to stop
	while ((_SFR_IO8(r) & mask) == state)
		width++;
	
	// convert the reading to microseconds.  the slower the CPU speed, the
	// proportionally fewer iterations of the loop will occur (e.g. a 
	// 4 MHz clock will yield a width that is one-fourth of that read with
	// a 16 MHz clock).  each loop was empirically determined to take
	// approximately 23/20 of a microsecond with a 16 MHz clock.
	return width * (16000000UL / F_CPU) * 20 / 23;
}

void shiftOut(int dataPin, int clockPin, int bitOrder, byte val) {
	int i;

	for (i = 0; i < 8; i++)  {
		if (bitOrder == LSBFIRST)
			digitalWrite(dataPin, !!(val & (1 << i)));
		else	
			digitalWrite(dataPin, !!(val & (1 << (7 - i))));
			
		digitalWrite(clockPin, HIGH);
		digitalWrite(clockPin, LOW);		
	}
}

void init()
{
	// this needs to be called before setup() or some functions won't
	// work there
	sei();
	
	// timer 0 is used for millis() and delay()
	timer0_overflow_count = 0;
	// on the ATmega168, timer 0 is also used for fast hardware pwm
	// (using phase-correct PWM would mean that timer 0 overflowed half as often
	// resulting in different millis() behavior on the ATmega8 and ATmega168)
#if defined(__AVR_ATmega168__)
	sbi(TCCR0A, WGM01);
	sbi(TCCR0A, WGM00);
#endif  
	// set timer 0 prescale factor to 64
#if defined(__AVR_ATmega168__)
	sbi(TCCR0B, CS01);
	sbi(TCCR0B, CS00);
#else
	sbi(TCCR0, CS01);
	sbi(TCCR0, CS00);
#endif
	// enable timer 0 overflow interrupt
#if defined(__AVR_ATmega168__)
	sbi(TIMSK0, TOIE0);
#else
	sbi(TIMSK, TOIE0);
#endif

	// timers 1 and 2 are used for phase-correct hardware pwm
	// this is better for motors as it ensures an even waveform
	// note, however, that fast pwm mode can achieve a frequency of up
	// 8 MHz (with a 16 MHz clock) at 50% duty cycle

	// set timer 1 prescale factor to 64
	sbi(TCCR1B, CS11);
	sbi(TCCR1B, CS10);
	// put timer 1 in 8-bit phase correct pwm mode
	sbi(TCCR1A, WGM10);

	// set timer 2 prescale factor to 64
#if defined(__AVR_ATmega168__)
	sbi(TCCR2B, CS22);
#else
	sbi(TCCR2, CS22);
#endif
	// configure timer 2 for phase correct pwm (8-bit)
#if defined(__AVR_ATmega168__)
	sbi(TCCR2A, WGM20);
#else
	sbi(TCCR2, WGM20);
#endif

	// set a2d reference to AVCC (5 volts)
	cbi(ADMUX, REFS1);
	sbi(ADMUX, REFS0);

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

	// enable a2d conversions
	sbi(ADCSRA, ADEN);

	// the bootloader connects pins 0 and 1 to the USART; disconnect them
	// here so they can be used as normal digital i/o; they will be
	// reconnected in Serial.begin()
#if defined(__AVR_ATmega168__)
	UCSR0B = 0;
#else
	UCSRB = 0;
#endif
}