feature(PWM): PWM Fix

Fixed PWM with a helper function to calculate clock divider and wrap value.

Added Comments

lab_4/lab_4.c

@@ -16,27 +16,16 @@
 
 #define PWM_PIN 2
 #define PWM_FREQ 20
-#define PWM_DUTY 0.5
+#define PWM_DUTY 50
 
 #define ADC_PIN 26
 #define ADC_FREQ 25
 
-void setup () {
-    gpio_set_function(PWM_PIN, GPIO_FUNC_PWM);
-    uint slice_num = pwm_gpio_to_slice_num(PWM_PIN);
-
-    pwm_set_wrap(slice_num, 100);
-    // Setup PWM with 20 Hz frequency and 50% duty cycle
-    pwm_set_chan_level(slice_num, PWM_CHAN_A, PWM_DUTY * 100);
-    pwm_set_enabled(slice_num, true);
-    pwm_set_clkdiv(slice_num, 1);
-
-    // Set up ADC
-    adc_init();
-    adc_gpio_init(ADC_PIN);
-    adc_select_input(0);
-}
-
+/**
+ * Callback function for repeating timer to read ADC value
+ * @param t The timer that triggered the callback
+ * @return  True to keep the timer running, false to stop it
+ */
 bool repeating_timer_callback (struct repeating_timer *t) {
     // Read ADC value
     uint16_t result = adc_read();
@@ -52,18 +41,77 @@ bool repeating_timer_callback (struct repeating_timer *t) {
     return true;
 }
 
-int main () {
-    stdio_init_all();
-    setup();
+/**
+ * Helper function to calculate the clock divider and wrap value for PWM
+ * Based on: https://www.i-programmer.info/programming/hardware/14849-the-pico-in-c-basic-pwm.html
+ *
+ * RP2040 clock is 125 MHz, PWM Counter is 16-bit
+ * Clock divider is 16-bit, with 12-bit integer and 4-bit fraction
+ * @param slice_num     PWM slice number
+ * @param channel       PWM channel
+ * @param frequency     PWM frequency
+ * @param duty_cycle    PWM duty cycle
+ * @return              PWM wrap value
+ */
+uint32_t pwm_set_freq_duty (uint slice_num,
+                            uint channel, uint32_t frequency, int duty_cycle) {
+    uint32_t clock = 125000000;
 
-    struct repeating_timer timer;
+    // divider = Ceil(16 * clock / 65536 * frequency) + remainder
+    //         = Ceil(clock / frequency / 4096) + remainder
+    uint32_t divider16 = clock / frequency / 4096 +
+                         (clock % (frequency * 4096) !=
+                          0); // Round up if less than 1
+
+    // If divider is less than 16, set it to 16 (16-bit counter)
+    if (divider16 / 16 == 0)
+    {
+        divider16 = 16;
+    }
+
+    // Wrap value is 16 bits, so max value is 65535 (2^16 - 1)
+    uint32_t wrap = clock * 16 / divider16 / frequency - 1;
+
+    // Set clock divider and wrap value
+    pwm_set_clkdiv_int_frac(slice_num, divider16 / 16,
+                            divider16 & 0xF);
+    pwm_set_wrap(slice_num, wrap);
+
+    // Level = wrap * duty_cycle(as fraction)
+    //       = wrap * duty_cycle / 100
+    pwm_set_chan_level(slice_num, channel, wrap * duty_cycle / 100);
+    return wrap;
+}
+
+/**
+ * Setup Function for PWM and ADC
+ * @param timer   Repeating timer for ADC
+ */
+void setup (struct repeating_timer *timer) {
+    // PWM setup
+    gpio_set_function(PWM_PIN, GPIO_FUNC_PWM);
+    uint slice_num = pwm_gpio_to_slice_num(PWM_PIN);
+    uint channel = pwm_gpio_to_channel(PWM_PIN);
+    pwm_set_freq_duty(slice_num, channel, PWM_FREQ, PWM_DUTY);
+    pwm_set_enabled(slice_num, true);
+
+    // ADC setup
+    adc_init();
+    adc_gpio_init(ADC_PIN);
+    adc_select_input(0);
 
     // Setup timer interrupt
     add_repeating_timer_ms(ADC_FREQ,
                            repeating_timer_callback,
                            NULL,
-                           &timer
+                           timer
     );
+}
+
+int main () {
+    stdio_init_all();
+    struct repeating_timer timer;
+    setup(&timer);
 
     while (true)
     {