1 files changed, 86 insertions, 0 deletions
diff --git a/picl-firmware/fan_control.c b/picl-firmware/fan_control.c
new file mode 100644
index 0000000..9e87963
--- /dev/null
+++ b/picl-firmware/fan_control.c
@@ -0,0 +1,86 @@
+#include <avr/io.h>
+#include <avr/interrupt.h>
+#include <avr/sleep.h>
+
+void setup_adc() {
+    //enable interrupts
+    sei();
+    // setup external reference voltage.
+    ADMUX &= ~(3UL << REFS0);
+    ADMUX |= (1UL << REFS0);
+    // set left adjusted ADC result so we can easily only use the upper 8 bits of the result
+    ADCSRB |= (1UL << ADLAR);
+    // enable ADC interrupt
+    ADCSRA |= (1UL << ADIE);
+}
+
+void setup_timers() {
+    //use system clock for timers, no prescaler.
+    TCCR0B &= ~(7UL << CS00);
+    TCCR0B |= (1UL << CS00);
+
+    //set mode 5 (PWM, phase correct, top defined by OCRA)
+    TCCR0A &= ~(3UL << WGM00);
+    TCCR0B &- ~(1UL << WGM02);
+    TCCR0A |= (1UL << WGM00);
+    TCCR0B |= (1UL << WGM02);
+}
+
+void enable_ADC() {
+    PRR &= ~(1UL << PRADC);
+    ADCSRA |= (1UL << ADEN);
+}
+
+void disable_ADC() {
+    ADCSRA &= ~(1UL << ADEN);
+    PRR |= (1UL << PRADC);
+}
+
+void select_ADC_channel(int channel) {
+    ADMUX &= ~(7UL << MUX0);
+    ADMUX |= (channel << MUX0);
+}
+
+uint8_t get_ADC_result() {
+    uint8_t result = ADCL;
+    //conversion would be blocked if we don't also read ADCH although we won't use the upper 2 bits.
+    uint8_t unblock = ADCH; 
+    return result;
+}
+
+void start_ADC() {
+    ADCSRA |= (1UL << ADSC);
+}
+
+volatile uint8_t fan1;
+volatile uint8_t fan2;
+
+void start_polling_fans() {
+    PRR &= ~(1UL << PRADC);
+    enable_ADC();
+    select_ADC_channel(ADC1D);
+    start_ADC();
+}
+
+ISR(ADC_vect) {
+    if(ADMUX & (7UL << MUX0) == ADC1D) {
+        fan1 = get_ADC_result();
+        select_ADC_channel(ADC2D);
+        start_ADC();
+        return;
+    }
+
+    if(ADMUX & (7UL << MUX0) == ADC2D) {
+        fan2 = get_ADC_result();
+        disable_ADC();
+        return;
+    }
+}
+
+int main() {
+    set_sleep_mode(0);
+    setup_adc();
+    setup_timers();
+
+    while(1);
+}