mirror of
https://github.com/arduino/Arduino.git
synced 2024-12-12 23:08:52 +01:00
192 lines
5.5 KiB
C
Executable File
192 lines
5.5 KiB
C
Executable File
/*
|
|
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 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;
|
|
|
|
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)
|
|
{
|
|
uint8_t oldSREG;
|
|
|
|
// 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
|
|
|
|
// disable interrupts, otherwise the timer 0 overflow interrupt that
|
|
// tracks milliseconds will make us delay longer than we want.
|
|
oldSREG = SREG;
|
|
cli();
|
|
|
|
// busy wait
|
|
__asm__ __volatile__ (
|
|
"1: sbiw %0,1" "\n\t" // 2 cycles
|
|
"brne 1b" : "=w" (us) : "0" (us) // 2 cycles
|
|
);
|
|
|
|
// reenable interrupts.
|
|
SREG = oldSREG;
|
|
}
|
|
|
|
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 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
|
|
} |