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238 lines
6.4 KiB
C
238 lines
6.4 KiB
C
/*
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wiring.c - Partial implementation of the Wiring API for the ATmega8.
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Part of Arduino - http://www.arduino.cc/
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Copyright (c) 2005-2006 David A. Mellis
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This library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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This library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General
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Public License along with this library; if not, write to the
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Free Software Foundation, Inc., 59 Temple Place, Suite 330,
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Boston, MA 02111-1307 USA
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$Id: wiring.c 808 2009-12-18 17:44:08Z dmellis $
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*/
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#include "wiring_private.h"
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// the prescaler is set so that timer0 ticks every 64 clock cycles, and the
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// the overflow handler is called every 256 ticks.
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#define MICROSECONDS_PER_TIMER0_OVERFLOW (clockCyclesToMicroseconds(64 * 256))
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// the whole number of milliseconds per timer0 overflow
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#define MILLIS_INC (MICROSECONDS_PER_TIMER0_OVERFLOW / 1000)
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// the fractional number of milliseconds per timer0 overflow. we shift right
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// by three to fit these numbers into a byte. (for the clock speeds we care
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// about - 8 and 16 MHz - this doesn't lose precision.)
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#define FRACT_INC ((MICROSECONDS_PER_TIMER0_OVERFLOW % 1000) >> 3)
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#define FRACT_MAX (1000 >> 3)
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volatile unsigned long timer0_overflow_count = 0;
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volatile unsigned long timer0_millis = 0;
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static unsigned char timer0_fract = 0;
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SIGNAL(TIMER0_OVF_vect)
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{
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// copy these to local variables so they can be stored in registers
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// (volatile variables must be read from memory on every access)
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unsigned long m = timer0_millis;
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unsigned char f = timer0_fract;
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m += MILLIS_INC;
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f += FRACT_INC;
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if (f >= FRACT_MAX) {
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f -= FRACT_MAX;
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m += 1;
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}
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timer0_fract = f;
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timer0_millis = m;
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timer0_overflow_count++;
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}
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unsigned long millis()
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{
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unsigned long m;
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uint8_t oldSREG = SREG;
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// disable interrupts while we read timer0_millis or we might get an
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// inconsistent value (e.g. in the middle of a write to timer0_millis)
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cli();
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m = timer0_millis;
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SREG = oldSREG;
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return m;
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}
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unsigned long micros() {
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unsigned long m;
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uint8_t oldSREG = SREG, t;
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cli();
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m = timer0_overflow_count;
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t = TCNT0;
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#ifdef TIFR0
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if ((TIFR0 & _BV(TOV0)) && (t < 255))
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m++;
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#else
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if ((TIFR & _BV(TOV0)) && (t < 255))
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m++;
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#endif
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SREG = oldSREG;
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return ((m << 8) + t) * (64 / clockCyclesPerMicrosecond());
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}
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void delay(unsigned long ms)
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{
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unsigned long start = millis();
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while (millis() - start <= ms)
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;
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}
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/* Delay for the given number of microseconds. Assumes a 8 or 16 MHz clock. */
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void delayMicroseconds(unsigned int us)
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{
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// calling avrlib's delay_us() function with low values (e.g. 1 or
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// 2 microseconds) gives delays longer than desired.
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//delay_us(us);
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#if F_CPU >= 16000000L
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// for the 16 MHz clock on most Arduino boards
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// for a one-microsecond delay, simply return. the overhead
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// of the function call yields a delay of approximately 1 1/8 us.
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if (--us == 0)
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return;
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// the following loop takes a quarter of a microsecond (4 cycles)
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// per iteration, so execute it four times for each microsecond of
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// delay requested.
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us <<= 2;
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// account for the time taken in the preceeding commands.
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us -= 2;
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#else
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// for the 8 MHz internal clock on the ATmega168
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// for a one- or two-microsecond delay, simply return. the overhead of
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// the function calls takes more than two microseconds. can't just
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// subtract two, since us is unsigned; we'd overflow.
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if (--us == 0)
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return;
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if (--us == 0)
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return;
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// the following loop takes half of a microsecond (4 cycles)
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// per iteration, so execute it twice for each microsecond of
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// delay requested.
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us <<= 1;
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// partially compensate for the time taken by the preceeding commands.
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// we can't subtract any more than this or we'd overflow w/ small delays.
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us--;
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#endif
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// busy wait
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__asm__ __volatile__ (
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"1: sbiw %0,1" "\n\t" // 2 cycles
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"brne 1b" : "=w" (us) : "0" (us) // 2 cycles
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);
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}
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void init()
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{
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// this needs to be called before setup() or some functions won't
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// work there
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sei();
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// on the ATmega168, timer 0 is also used for fast hardware pwm
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// (using phase-correct PWM would mean that timer 0 overflowed half as often
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// resulting in different millis() behavior on the ATmega8 and ATmega168)
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#if !defined(__AVR_ATmega8__)
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sbi(TCCR0A, WGM01);
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sbi(TCCR0A, WGM00);
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#endif
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// set timer 0 prescale factor to 64
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#if defined(__AVR_ATmega8__)
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sbi(TCCR0, CS01);
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sbi(TCCR0, CS00);
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#else
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sbi(TCCR0B, CS01);
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sbi(TCCR0B, CS00);
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#endif
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// enable timer 0 overflow interrupt
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#if defined(__AVR_ATmega8__)
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sbi(TIMSK, TOIE0);
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#else
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sbi(TIMSK0, TOIE0);
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#endif
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// timers 1 and 2 are used for phase-correct hardware pwm
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// this is better for motors as it ensures an even waveform
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// note, however, that fast pwm mode can achieve a frequency of up
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// 8 MHz (with a 16 MHz clock) at 50% duty cycle
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// set timer 1 prescale factor to 64
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sbi(TCCR1B, CS11);
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sbi(TCCR1B, CS10);
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// put timer 1 in 8-bit phase correct pwm mode
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sbi(TCCR1A, WGM10);
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// set timer 2 prescale factor to 64
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#if defined(__AVR_ATmega8__)
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sbi(TCCR2, CS22);
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#else
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sbi(TCCR2B, CS22);
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#endif
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// configure timer 2 for phase correct pwm (8-bit)
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#if defined(__AVR_ATmega8__)
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sbi(TCCR2, WGM20);
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#else
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sbi(TCCR2A, WGM20);
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#endif
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#if defined(__AVR_ATmega1280__)
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// set timer 3, 4, 5 prescale factor to 64
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sbi(TCCR3B, CS31); sbi(TCCR3B, CS30);
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sbi(TCCR4B, CS41); sbi(TCCR4B, CS40);
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sbi(TCCR5B, CS51); sbi(TCCR5B, CS50);
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// put timer 3, 4, 5 in 8-bit phase correct pwm mode
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sbi(TCCR3A, WGM30);
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sbi(TCCR4A, WGM40);
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sbi(TCCR5A, WGM50);
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#endif
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// set a2d prescale factor to 128
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// 16 MHz / 128 = 125 KHz, inside the desired 50-200 KHz range.
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// XXX: this will not work properly for other clock speeds, and
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// this code should use F_CPU to determine the prescale factor.
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sbi(ADCSRA, ADPS2);
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sbi(ADCSRA, ADPS1);
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sbi(ADCSRA, ADPS0);
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// enable a2d conversions
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sbi(ADCSRA, ADEN);
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// the bootloader connects pins 0 and 1 to the USART; disconnect them
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// here so they can be used as normal digital i/o; they will be
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// reconnected in Serial.begin()
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#if defined(__AVR_ATmega8__)
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UCSRB = 0;
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#else
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UCSR0B = 0;
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#endif
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} |