wip mod04 ex01

module04/ex01/main.c

@@ -0,0 +1,58 @@
+#include "header.h"
+
+// 14.3.1 : alternate functions for led2 PB1
+// - OC1A (Timer/Counter1 Output Compare Match A Output)
+//   - 16.11.1 controlled by COM1A1:0 in TCCR1A
+//   - Table 16-2 : Compare Output Mode, Fast PWM
+//     (1 << COM1A1) | (0 << COM1A0) -> non-inverting mode
+//   - Table 16-4 : set timer 1 in fast PWM mode, with top as ICR1 or OCR1A
+//   - ICR1 : Input Capture Register ((1 << WGM13) | (1 << WGM12) | (1 << WGM11) | (0 << WGM10))
+//   - OCR1A : Output Compare Register ((1 << WGM13) | (1 << WGM12) | (1 << WGM11) | (1 << WGM10))
+//     -> if OCR1A is top, it's also duty cycle, so changing duty cycle will also change frequency
+//     -> if ICR1 is top, OCR1A is duty cycle, so it can be changed independantly
+// - PCINT1 (Pin Change Interrupt 1) : to interrupt when pin change, in input mode only
+
+// calulations
+// - frequency is 16Mhz -> it means that the clock runs 16 000 000 times per seconds
+// - and the timer1 can store 16 bits value of cycle -> which is 2^16 = 65536
+// - so it will only last 65536/16000000 = 0,004096 second
+// - if i want my cycle to be 0.001 second, prescaler 1 is enough
+// - if i want my cycle to be 0.01 second, which prescaler ?
+//   - 8 * 0,004096 = 0.032768 -> it is enough
+//   - 64 * 0,004096 = 0.262144 -> it is largely enough
+// - if i choose prescaler 1 for a duration of 0.001 seconds, i need to restart the clock after how many cycles :
+//   - (16000000 / 1) * 0.001 = 16000 ticks -> set ICR1 = 16000
+// - if i choose prescaler 8 for a duration of 0.01 seconds, i need to restart the clock after how many cycles :
+//   - (16000000 / 8) * 0.01 = 20000 ticks -> set ICR1 = 20000
+// - if i choose prescaler 64 for a duration of 0.01 seconds, i need to restart the clock after how many cycles :
+//   - (16000000 / 64) * 0.01 = 2500 ticks -> set ICR1 = 2500
+
+// 16.9.3 : timer1 fast PWM
+
+#define LED1_PWM_PRESCALER	8	// can be 1, 8, 64, 256, 1024
+#define DUTY_CYCLE_PERCENT	9
+#define FRQUENCY_MS			1
+
+// use timers interruptions to varie led1 intensity using duty cycle, from 0% to 100% to 0% in 1 second
+// timer1 sets the led duty cycle, timer0 change the duty cycle percentage
+int main() {
+	MODE_OUTPUT(LED1);
+	CLEAR_ELEM(LED1);
+	MODE_OUTPUT(LED2);
+	CLEAR_ELEM(LED2);
+
+	SREG |= ENABLE_GLOBAL_INTERRUPT;
+
+	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
+	TCCR1B = (1 << WGM13) | (1 << WGM12);
+
+	TCCR1A |= (1 << COM1A1);							// Table 16-2 : set non-inverting mode to trigger OC1A on fast PWM
+
+	TCCR1B |= PRESCALE_SET(LED1_PWM_PRESCALER);			// Table 16-5 : set the appropriate prescale values
+
+	ICR1 = TIME_MS(FRQUENCY_MS, LED1_PWM_PRESCALER);	// top value for Xms
+
+	OCR1A = PERCENT(DUTY_CYCLE_PERCENT, ICR1);			// duty cycle frequence
+
+    while (1);
+}