104 lines
2.6 KiB
C
104 lines
2.6 KiB
C
//timer02.c
|
|
// use atmega timer2 as main system timer instead of timer0
|
|
// timer0 is used for fast pwm (OC0B output)
|
|
// original OVF handler is disabled
|
|
#include <avr/io.h>
|
|
#include <avr/interrupt.h>
|
|
#include <Arduino.h>
|
|
|
|
|
|
uint8_t timer02_pwm0 = 0;
|
|
|
|
void timer02_set_pwm0(uint8_t pwm0)
|
|
{
|
|
if (timer02_pwm0 == pwm0) return;
|
|
if (pwm0)
|
|
{
|
|
TCCR0A |= (2 << COM0B0);
|
|
OCR0B = pwm0 - 1;
|
|
}
|
|
else
|
|
{
|
|
TCCR0A &= ~(2 << COM0B0);
|
|
OCR0B = 0;
|
|
}
|
|
}
|
|
|
|
void timer02_init(void)
|
|
{
|
|
//save sreg
|
|
uint8_t _sreg = SREG;
|
|
//disable interrupts for sure
|
|
cli();
|
|
//mask timer0 interrupts - disable all
|
|
TIMSK0 &= ~(1<<TOIE0);
|
|
TIMSK0 &= ~(1<<OCIE0A);
|
|
TIMSK0 &= ~(1<<OCIE0B);
|
|
//setup timer0
|
|
TCCR0A = 0x00; //COM_A-B=00, WGM_0-1=00
|
|
TCCR0B = (1 << CS00); //WGM_2=0, CS_0-2=011
|
|
//switch timer0 to fast pwm mode
|
|
TCCR0A |= (3 << WGM00); //WGM_0-1=11
|
|
//set OCR0B register to zero
|
|
OCR0B = 0;
|
|
//disable OCR0B output (will be enabled in timer02_set_pwm0)
|
|
TCCR0A &= ~(2 << COM0B0);
|
|
//setup timer2
|
|
TCCR2A = 0x00; //COM_A-B=00, WGM_0-1=00
|
|
TCCR2B = (3 << CS20); //WGM_2=0, CS_0-2=011
|
|
//mask timer2 interrupts - enable OVF, disable others
|
|
TIMSK2 |= (1<<TOIE2);
|
|
TIMSK2 &= ~(1<<OCIE2A);
|
|
TIMSK2 &= ~(1<<OCIE2B);
|
|
//set timer2 OCR registers (OCRB interrupt generated 0.5ms after OVF interrupt)
|
|
OCR2A = 0;
|
|
OCR2B = 128;
|
|
//restore sreg (enable interrupts)
|
|
SREG = _sreg;
|
|
}
|
|
|
|
|
|
//following code is OVF handler for timer 2
|
|
//it is copy-paste from wiring.c and modified for timer2
|
|
//variables timer0_overflow_count and timer0_millis are declared in wiring.c
|
|
|
|
|
|
|
|
// 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)
|
|
|
|
extern volatile unsigned long timer0_overflow_count;
|
|
extern volatile unsigned long timer0_millis;
|
|
unsigned char timer0_fract = 0;
|
|
|
|
ISR(TIMER2_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++;
|
|
}
|
|
|