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