| /* |
| 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; |
| |
| SIGNAL(TIMER0_OVF_vect) |
| { |
| // 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 |
| |
| TCCR1B = 0; |
| |
| // set timer 1 prescale factor to 64 |
| #if defined(TCCR1B) && defined(CS11) && defined(CS10) |
| sbi(TCCR1B, CS11); |
| sbi(TCCR1B, CS10); |
| #elif defined(TCCR1) && defined(CS11) && defined(CS10) |
| sbi(TCCR1, CS11); |
| sbi(TCCR1, CS10); |
| #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 |
| } |