59 lines
2.7 KiB
C
59 lines
2.7 KiB
C
#include "header.h"
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// 14.3.1 : alternate functions for led2 PB1
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// - OC1A (Timer/Counter1 Output Compare Match A Output)
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// - 16.11.1 controlled by COM1A1:0 in TCCR1A
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// - Table 16-2 : Compare Output Mode, Fast PWM
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// (1 << COM1A1) | (0 << COM1A0) -> non-inverting mode
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// - Table 16-4 : set timer 1 in fast PWM mode, with top as ICR1 or OCR1A
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// - ICR1 : Input Capture Register ((1 << WGM13) | (1 << WGM12) | (1 << WGM11) | (0 << WGM10))
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// - OCR1A : Output Compare Register ((1 << WGM13) | (1 << WGM12) | (1 << WGM11) | (1 << WGM10))
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// -> if OCR1A is top, it's also duty cycle, so changing duty cycle will also change frequency
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// -> if ICR1 is top, OCR1A is duty cycle, so it can be changed independantly
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// - PCINT1 (Pin Change Interrupt 1) : to interrupt when pin change, in input mode only
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// calulations
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// - frequency is 16Mhz -> it means that the clock runs 16 000 000 times per seconds
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// - and the timer1 can store 16 bits value of cycle -> which is 2^16 = 65536
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// - so it will only last 65536/16000000 = 0,004096 second
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// - if i want my cycle to be 0.001 second, prescaler 1 is enough
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// - if i want my cycle to be 0.01 second, which prescaler ?
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// - 8 * 0,004096 = 0.032768 -> it is enough
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// - 64 * 0,004096 = 0.262144 -> it is largely enough
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// - if i choose prescaler 1 for a duration of 0.001 seconds, i need to restart the clock after how many cycles :
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// - (16000000 / 1) * 0.001 = 16000 ticks -> set ICR1 = 16000
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// - if i choose prescaler 8 for a duration of 0.01 seconds, i need to restart the clock after how many cycles :
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// - (16000000 / 8) * 0.01 = 20000 ticks -> set ICR1 = 20000
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// - if i choose prescaler 64 for a duration of 0.01 seconds, i need to restart the clock after how many cycles :
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// - (16000000 / 64) * 0.01 = 2500 ticks -> set ICR1 = 2500
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// 16.9.3 : timer1 fast PWM
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#define LED1_PWM_PRESCALER 8 // can be 1, 8, 64, 256, 1024
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#define DUTY_CYCLE_PERCENT 9
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#define FRQUENCY_MS 1
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// use timers interruptions to varie led1 intensity using duty cycle, from 0% to 100% to 0% in 1 second
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// timer1 sets the led duty cycle, timer0 change the duty cycle percentage
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int main() {
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MODE_OUTPUT(LED1);
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CLEAR_ELEM(LED1);
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MODE_OUTPUT(LED2);
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CLEAR_ELEM(LED2);
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SREG |= ENABLE_GLOBAL_INTERRUPT;
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TCCR1A = (1 << WGM11); // Table 16-4 : set fast PWM mode with TOP ICR1, so we can use OCR1A for duty cycle and keep ICR1 for frequency
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TCCR1B = (1 << WGM13) | (1 << WGM12);
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TCCR1A |= (1 << COM1A1); // Table 16-2 : set non-inverting mode to trigger OC1A on fast PWM
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TCCR1B |= PRESCALE_SET(LED1_PWM_PRESCALER); // Table 16-5 : set the appropriate prescale values
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ICR1 = TIME_MS(FRQUENCY_MS, LED1_PWM_PRESCALER); // top value for Xms
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OCR1A = PERCENT(DUTY_CYCLE_PERCENT, ICR1); // duty cycle frequence
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while (1);
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}
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