Quadrotor

/*

  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()

{

        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() {

        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()

{

        // 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

}