Add pwm sound sample code

Code/picocalc_helloworld/pwm_sound/CMakeLists.txt

@@ -0,0 +1,19 @@
+
+cmake_minimum_required(VERSION 3.13)
+
+set(CMAKE_C_STANDARD 11)
+
+project(pwm_sound
+        VERSION 0.0.1
+        DESCRIPTION "pwm_sound for rp2040."
+        )
+
+add_library(pwm_sound INTERFACE)
+
+target_sources(pwm_sound INTERFACE
+        pwm_sound.c
+        )
+
+target_link_libraries(pwm_sound INTERFACE  pico_stdlib hardware_pwm)
+
+target_include_directories(pwm_sound INTERFACE ${CMAKE_CURRENT_LIST_DIR})

Code/picocalc_helloworld/pwm_sound/pwm_sound.c

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+
+#include "pwm_sound.h"
+
+
+void init_pwm(irq_handler_t my_handler) {
+
+    gpio_set_function(AUDIO_PIN_L, GPIO_FUNC_PWM);
+    gpio_set_function(AUDIO_PIN_R, GPIO_FUNC_PWM);
+
+    int slice_l = pwm_gpio_to_slice_num(AUDIO_PIN_L);
+    int slice_r = pwm_gpio_to_slice_num(AUDIO_PIN_R);
+
+
+    pwm_clear_irq(slice_l);
+    pwm_clear_irq(slice_r);
+    pwm_set_irq_enabled(slice_l, true);
+    pwm_set_irq_enabled(slice_r, true);
+
+    irq_set_exclusive_handler(PWM_IRQ_WRAP, my_handler);
+    irq_set_enabled(PWM_IRQ_WRAP, true);
+
+
+    pwm_config config = pwm_get_default_config();
+    pwm_config_set_clkdiv(&config, 6.05f); // 133MHz
+    pwm_config_set_wrap(&config, 250);
+
+
+    pwm_init(slice_l, &config, true);
+    pwm_init(slice_r, &config, true);
+
+    pwm_set_chan_level(slice_l, PWM_CHAN_A, 0);
+    pwm_set_chan_level(slice_r, PWM_CHAN_B, 0);
+}

Code/picocalc_helloworld/pwm_sound/pwm_sound.h

@@ -0,0 +1,15 @@
+
+#ifndef PWM_SOUND_H
+#define PWM_SOUND_H
+
+#include "pico/stdlib.h"
+#include "hardware/pwm.h"
+#include <stdio.h>
+
+#define PWM_CLOCK_KHZ 133000
+#define AUDIO_PIN_L 26
+#define AUDIO_PIN_R 27
+
+void init_pwm(irq_handler_t);
+
+#endif //PWM_SOUND_H