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