/elec/audio-switcher

/*

  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 "wiring_private.h"

// the prescaler is set so that timer0 ticks every 64 clock cycles, and the

// the overflow handler is called every 256 ticks.

#define MICROSECONDS_PER_TIMER0_OVERFLOW (clockCyclesToMicroseconds(64 * 256))

// the whole number of milliseconds per timer0 overflow

#define MILLIS_INC (MICROSECONDS_PER_TIMER0_OVERFLOW / 1000)

// the fractional number of milliseconds per timer0 overflow. we shift right

// by three to fit these numbers into a byte. (for the clock speeds we care

// about - 8 and 16 MHz - this doesn't lose precision.)

#define FRACT_INC ((MICROSECONDS_PER_TIMER0_OVERFLOW % 1000) >> 3)

#define FRACT_MAX (1000 >> 3)

volatile unsigned long timer0_overflow_count = 0;

volatile unsigned long timer0_millis = 0;

static unsigned char timer0_fract = 0;

#if defined(__AVR_ATtiny24__) || defined(__AVR_ATtiny44__) || defined(__AVR_ATtiny84__)

SIGNAL(TIM0_OVF_vect)

#else

SIGNAL(TIMER0_OVF_vect)

#endif

{

	// copy these to local variables so they can be stored in registers

	// (volatile variables must be read from memory on every access)

	unsigned long m = timer0_millis;

	unsigned char f = timer0_fract;

	m += MILLIS_INC;

	f += FRACT_INC;

	if (f >= FRACT_MAX) {

		f -= FRACT_MAX;

		m += 1;

	}

	timer0_fract = f;

	timer0_millis = m;

	timer0_overflow_count++;

}

unsigned long millis(void)

{

	unsigned long m;

	uint8_t oldSREG = SREG;

	// disable interrupts while we read timer0_millis or we might get an

	// inconsistent value (e.g. in the middle of a write to timer0_millis)

	cli();

	m = timer0_millis;

	SREG = oldSREG;

	return m;

}

unsigned long micros(void) {

	unsigned long m;

	uint8_t oldSREG = SREG, t;

	cli();

	m = timer0_overflow_count;

#if defined(TCNT0)

	t = TCNT0;

#elif defined(TCNT0L)

	t = TCNT0L;

#else

	#error TIMER 0 not defined

#endif

#ifdef TIFR0

	if ((TIFR0 & _BV(TOV0)) && (t < 255))

		m++;

#else

	if ((TIFR & _BV(TOV0)) && (t < 255))

		m++;

#endif

	SREG = oldSREG;

	return ((m << 8) + t) * (64 / clockCyclesPerMicrosecond());

}

void delay(unsigned long ms)

{

	uint16_t start = (uint16_t)micros();

	while (ms > 0) {

		if (((uint16_t)micros() - start) >= 1000) {

			ms--;

			start += 1000;

		}

	}

}

/* Delay for the given number of microseconds.  Assumes a 8 or 16 MHz clock. */

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);

#if F_CPU >= 16000000L

	// for the 16 MHz clock on most Arduino boards

	// 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;

#else

	// for the 8 MHz internal clock on the ATmega168

	// for a one- or two-microsecond delay, simply return.  the overhead of

	// the function calls takes more than two microseconds.  can't just

	// subtract two, since us is unsigned; we'd overflow.

	if (--us == 0)

		return;

	if (--us == 0)

		return;

	// the following loop takes half of a microsecond (4 cycles)

	// per iteration, so execute it twice for each microsecond of

	// delay requested.

	us <<= 1;

	// partially compensate for the time taken by the preceeding commands.

	// we can't subtract any more than this or we'd overflow w/ small delays.

	us--;

#endif

	// busy wait

	__asm__ __volatile__ (

		"1: sbiw %0,1" "\n\t" // 2 cycles

		"brne 1b" : "=w" (us) : "0" (us) // 2 cycles

	);

}

void init_wiring_c(void)

{

	// this needs to be called before setup() or some functions won't

	// work there

	sei();

	// 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(TCCR0A) && defined(WGM01)

	sbi(TCCR0A, WGM01);

	sbi(TCCR0A, WGM00);

#endif  

	// set timer 0 prescale factor to 64

#if defined(__AVR_ATmega128__)

	// CPU specific: different values for the ATmega128

	sbi(TCCR0, CS02);

#elif defined(TCCR0) && defined(CS01) && defined(CS00)

	// this combination is for the standard atmega8

	sbi(TCCR0, CS01);

	sbi(TCCR0, CS00);

#elif defined(TCCR0B) && defined(CS01) && defined(CS00)

	// this combination is for the standard 168/328/1280/2560

	sbi(TCCR0B, CS01);

	sbi(TCCR0B, CS00);

#elif defined(TCCR0A) && defined(CS01) && defined(CS00)

	// this combination is for the __AVR_ATmega645__ series

	sbi(TCCR0A, CS01);

	sbi(TCCR0A, CS00);

#else

	#error Timer 0 prescale factor 64 not set correctly

#endif

	// enable timer 0 overflow interrupt

#if defined(TIMSK) && defined(TOIE0)

	sbi(TIMSK, TOIE0);

#elif defined(TIMSK0) && defined(TOIE0)

	sbi(TIMSK0, TOIE0);

#else

	#error	Timer 0 overflow interrupt not set correctly

#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

#if defined(TCCR1B) && defined(CS11) && defined(CS10)

	TCCR1B = 0;

	// set timer 1 prescale factor to 64

	sbi(TCCR1B, CS11);

#if F_CPU >= 8000000L

	sbi(TCCR1B, CS10);

#endif

#elif defined(TCCR1) && defined(CS11) && defined(CS10)

	sbi(TCCR1, CS11);

#if F_CPU >= 8000000L

	sbi(TCCR1, CS10);

#endif

#endif

	// put timer 1 in 8-bit phase correct pwm mode

#if defined(TCCR1A) && defined(WGM10)

	sbi(TCCR1A, WGM10);

#elif defined(TCCR1)

	#warning this needs to be finished

#endif

	// set timer 2 prescale factor to 64

#if defined(TCCR2) && defined(CS22)

	sbi(TCCR2, CS22);

#elif defined(TCCR2B) && defined(CS22)

	sbi(TCCR2B, CS22);

#else

	#warning Timer 2 not finished (may not be present on this CPU)

#endif

	// configure timer 2 for phase correct pwm (8-bit)

#if defined(TCCR2) && defined(WGM20)

	sbi(TCCR2, WGM20);

#elif defined(TCCR2A) && defined(WGM20)

	sbi(TCCR2A, WGM20);

#else

	#warning Timer 2 not finished (may not be present on this CPU)

#endif

#if defined(TCCR3B) && defined(CS31) && defined(WGM30)

	sbi(TCCR3B, CS31);		// set timer 3 prescale factor to 64

	sbi(TCCR3B, CS30);

	sbi(TCCR3A, WGM30);		// put timer 3 in 8-bit phase correct pwm mode

#endif

#if defined(TCCR4B) && defined(CS41) && defined(WGM40)

	sbi(TCCR4B, CS41);		// set timer 4 prescale factor to 64

	sbi(TCCR4B, CS40);

	sbi(TCCR4A, WGM40);		// put timer 4 in 8-bit phase correct pwm mode

#endif

#if defined(TCCR5B) && defined(CS51) && defined(WGM50)

	sbi(TCCR5B, CS51);		// set timer 5 prescale factor to 64

	sbi(TCCR5B, CS50);

	sbi(TCCR5A, WGM50);		// put timer 5 in 8-bit phase correct pwm mode

#endif

#if defined(ADCSRA)

	// 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);

#endif

	// 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(UCSRB)

	UCSRB = 0;

#elif defined(UCSR0B)

	UCSR0B = 0;

#endif

}