Initial Release

pwm/led_fade/pwm_led_fade.c

@@ -0,0 +1,65 @@
+/**
+ * Copyright (c) 2020 Raspberry Pi (Trading) Ltd.
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+
+// Fade an LED between low and high brightness. An interrupt handler updates
+// the PWM slice's output level each time the counter wraps.
+
+#include "pico/stdlib.h"
+#include <stdio.h>
+#include "pico/time.h"
+#include "hardware/irq.h"
+#include "hardware/pwm.h"
+
+void on_pwm_wrap() {
+    static int fade = 0;
+    static bool going_up = true;
+    // Clear the interrupt flag that brought us here
+    pwm_clear_irq(pwm_gpio_to_slice_num(PICO_DEFAULT_LED_PIN));
+
+    if (going_up) {
+        ++fade;
+        if (fade > 255) {
+            fade = 255;
+            going_up = false;
+        }
+    } else {
+        --fade;
+        if (fade < 0) {
+            fade = 0;
+            going_up = true;
+        }
+    }
+    // Square the fade value to make the LED's brightness appear more linear
+    // Note this range matches with the wrap value
+    pwm_set_gpio_level(PICO_DEFAULT_LED_PIN, fade * fade);
+}
+
+int main() {
+    // Tell the LED pin that the PWM is in charge of its value.
+    gpio_set_function(PICO_DEFAULT_LED_PIN, GPIO_FUNC_PWM);
+    // Figure out which slice we just connected to the LED pin
+    uint slice_num = pwm_gpio_to_slice_num(PICO_DEFAULT_LED_PIN);
+
+    // Mask our slice's IRQ output into the PWM block's single interrupt line,
+    // and register our interrupt handler
+    pwm_clear_irq(slice_num);
+    pwm_set_irq_enabled(slice_num, true);
+    irq_set_exclusive_handler(PWM_IRQ_WRAP, on_pwm_wrap);
+    irq_set_enabled(PWM_IRQ_WRAP, true);
+
+    // Get some sensible defaults for the slice configuration. By default, the
+    // counter is allowed to wrap over its maximum range (0 to 2**16-1)
+    pwm_config config = pwm_get_default_config();
+    // Set divider, reduces counter clock to sysclock/this value
+    pwm_config_set_clkdiv(&config, 4.f);
+    // Load the configuration into our PWM slice, and set it running.
+    pwm_init(slice_num, &config, true);
+
+    // Everything after this point happens in the PWM interrupt handler, so we
+    // can twiddle our thumbs
+    while (1)
+        tight_loop_contents();
+}