Include pico_tone library

src/rp2_common/CMakeLists.txt

@@ -10,4 +10,5 @@ pico_add_subdirectory(pico_sd_card)
 pico_add_subdirectory(pico_scanvideo_dpi)
 pico_add_subdirectory(usb_common)
 pico_add_subdirectory(usb_device)
-pico_add_subdirectory(usb_device_msc)
+pico_add_subdirectory(usb_device_msc)
+pico_add_subdirectory(pico_tone)

src/rp2_common/pico_tone/CMakeLists.txt

@@ -0,0 +1,11 @@
+if (NOT TARGET pico_tone)
+    pico_add_library(pico_tone)
+
+    target_include_directories(pico_tone_headers INTERFACE
+            ${CMAKE_CURRENT_LIST_DIR}/include)
+
+    target_sources(pico_tone INTERFACE
+            ${CMAKE_CURRENT_LIST_DIR}/tone.c)
+
+    target_link_libraries(pico_tone INTERFACE hardware_pwm)
+endif()

src/rp2_common/pico_tone/include/pico/tone.h

@@ -0,0 +1,65 @@
+/*
+ * Copyright (c) 2020 Raspberry Pi (Trading) Ltd.
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+
+#ifndef _PICO_TONE_H
+#define _PICO_TONE_H
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/** \file tone.h
+ *  \defgroup pico_tone pico_tone
+ *
+ *   Adds support for playing tones using PWM.
+ *  
+ *   Every sound humans encounter consists of one or more frequencies, and the
+ *   way the ear interprets those sounds  is called pitch.
+ *
+ *   In order to produce a variety of pitches, a digital signal needs to convey
+ *   the frequency of sound it is trying to reproduce. The simplest approach is
+ *   to generate a 50% duty cycle pulse stream and set the frequency to the
+ *   desired pitch.
+ *
+ *   References:
+ *       - https://www.hackster.io/106958/pwm-sound-synthesis-9596f0#overview
+ */
+
+/*! \brief Initialise the tone generator
+ *  \ingroup pico_tone
+ *
+ *  Initilise PWM on the given GPIO using the default pwm config.
+ *
+ *  \param gpio The GPIO to use for the tone generator
+ */
+void tone_init(uint gpio);
+
+/*! \brief Play a tone for a given duration
+ *  \ingroup pico_tone
+ *
+ *  Play a tone on the given GPIO for the given duration.
+ *
+ *  \param gpio The GPIO to use for the tone generator
+ *  \param freq The frequency of the tone in Hz
+ *  \param duration_ms The duration of the tone in milliseconds
+ */
+void tone(uint gpio, uint freq, uint32_t duration_ms);
+
+/*! \brief Do not play any tone.
+ *  \ingroup pico_tone
+ *
+ *  Stop playing a tone on the given GPIO.
+ *
+ *  \param gpio The GPIO to use for the tone generator
+ */
+void no_tone(uint gpio);
+
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif

src/rp2_common/pico_tone/tone.c

@@ -0,0 +1,34 @@
+/*
+ * Copyright (c) 2020 Raspberry Pi (Trading) Ltd.
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+#include "pico/stdlib.h"
+#include "pico/tone.h"
+#include "hardware/pwm.h"
+
+void tone_init(uint gpio) {
+    // Configure GPIO for PWM output
+    gpio_set_function(gpio, GPIO_FUNC_PWM);
+    // Find out which PWM slice is connected to GPIO
+    uint slice_num = pwm_gpio_to_slice_num(gpio);
+    // Get default configuration for PWM slice and initialise PWM with it
+    pwm_config config = pwm_get_default_config();
+    pwm_init(slice_num, &config, true);
+}
+
+void no_tone(uint gpio) {
+    pwm_set_gpio_level(gpio, 0);
+}
+
+void tone(uint gpio, uint freq, uint32_t duration_ms) {
+    // Calculate and cofigure new clock divider according to the frequency
+    // This formula is assuming we are running at 125MHz.
+    // TODO: Make this work for any frequency
+    float clkdiv = (1.f / freq) * 2000.f;
+    uint slice_num = pwm_gpio_to_slice_num(gpio);
+    pwm_set_clkdiv(slice_num, clkdiv);
+    // Configure duty to 50% ((2**16)-1)/2) to generate a square wave
+    pwm_set_gpio_level(gpio, 32768U);
+    sleep_ms(duration_ms);
+}