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/*
Copyright 2009 Adam Sampson <ats@offog.org>
Based on wiring.c/wiring.h from the Arduino project, which are:
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
*/
#include "tvm-arduino.h"
#define clockCyclesPerMicrosecond() ( F_CPU / 1000000L )
#define clockCyclesToMicroseconds(a) ( (a) / clockCyclesPerMicrosecond() )
/* 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 time_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 time_micros ()
{
unsigned long m, t;
uint8_t oldSREG = SREG;
cli();
t = TCNT0;
if ((TIFR0 & _BV(TOV0)) && (t == 0))
t = 256;
m = timer0_overflow_count;
SREG = oldSREG;
return ((m << 8) + t) * (64 / clockCyclesPerMicrosecond());
}
void time_init ()
{
/* set timer 0 prescale factor to 64 */
TCCR0B |= 3 << CS00;
/* enable timer 0 overflow interrupt */
TIMSK0 |= _BV (TOIE0);
}
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