pwm audio poc

firmware/.gitignore

@@ -4,4 +4,6 @@
 .vscode/launch.json
 .vscode/ipch
 src/gfx_png.h
+src/audio_sample.h
 gfx/
+audio/

firmware/README.md

@@ -11,3 +11,15 @@ move to `gfx` folder, then:
 ```
 python3 scripts/gfx_convert.py
 ```
+
+convert audio
+
+```
+ffmpeg -i badapple.webm -t 30 -ar 11000 output.wav
+```
+
+move to `audio` folder, then:
+
+```
+python3 scripts/audio_convert.py
+```

firmware/scripts/audio_convert.py

@@ -0,0 +1,57 @@
+import os
+import sys
+import soundfile as sf
+import samplerate
+
+# Adapted from https://github.com/rgrosset/pico-pwm-audio
+
+print("loading file...")
+
+soundfile = 'audio/output.wav'
+data_in, datasamplerate = sf.read(soundfile)
+# This means stereo so extract one channel 0
+if len(data_in.shape)>1:
+    data_in = data_in[:,0]
+
+print("resampling...")
+
+converter = 'sinc_best'  # or 'sinc_fastest', ...
+desired_sample_rate = 11000.0
+ratio = desired_sample_rate/datasamplerate
+data_out = samplerate.resample(data_in, ratio, converter)
+
+print("analyzing...")
+
+maxValue = max(data_out)
+minValue = min(data_out)
+print("length", len(data_out))
+print("max value", max(data_out))
+print("min value", min(data_out))
+vrange = (maxValue - minValue)
+print("value range", vrange)
+
+print("normalizing...")
+
+# normalize to 0-1
+normalized = [int((v-minValue)/vrange*255) for v in data_out]
+
+print("generating header...")
+
+m68code = "/*    File "+soundfile+ "\r\n *    Sample rate "+str(int(desired_sample_rate)) +" Hz\r\n */\r\n"
+m68code += "#define WAV_DATA_LENGTH "+str(len(data_out))+" \r\n\r\n"
+m68code += "static const uint8_t WAV_DATA[] = {\r\n    "
+
+m68code += ','.join(str(v) for v in normalized)
+
+# keep track of first and last values to avoid
+# blip when the loop restarts.. make the end value
+# the average of the first and last.
+end_value = int( (normalized[0] + normalized[len(normalized) - 1]) / 2)
+m68code+=","+str(end_value)+'\n};\n'
+
+print("writing output...")
+
+with open("src/audio_sample.h", "w") as f:
+    f.write(m68code)
+
+print("done!")

firmware/src/audio.cpp

@@ -0,0 +1,62 @@
+#include <Arduino.h>
+#include "hardware/irq.h"  // interrupts
+#include "hardware/pwm.h"  // pwm
+#include "hardware/sync.h" // wait for interrupt
+#include "hardware/gpio.h"
+
+#include "audio_sample.h"
+
+// Adapted from https://github.com/rgrosset/pico-pwm-audio
+
+#define AUDIO_PIN 23
+int wav_position = 0;
+
+/*
+ * PWM Interrupt Handler which outputs PWM level and advances the
+ * current sample.
+ *
+ * We repeat the same value for 8 cycles this means sample rate etc
+ * adjust by factor of 8   (this is what bitshifting <<3 is doing)
+ *
+ */
+void pwm_interrupt_handler() {
+    pwm_clear_irq(pwm_gpio_to_slice_num(AUDIO_PIN));
+    if (wav_position < (WAV_DATA_LENGTH<<3) - 1) {
+        // set pwm level
+        // allow the pwm value to repeat for 8 cycles this is >>3
+        pwm_set_gpio_level(AUDIO_PIN, WAV_DATA[wav_position>>3]);
+        wav_position++;
+    } else {
+        // reset to start
+        wav_position = 0;
+    }
+}
+
+// 11 KHz is fine for speech. Phone lines generally sample at 8 KHz
+#define SYS_CLOCK 125000000.0f
+#define AUDIO_WRAP 250.0f
+#define AUDIO_RATE 11000.0f
+#define AUDIO_CLK_DIV (SYS_CLOCK / AUDIO_WRAP / 8 / AUDIO_RATE)
+
+void init_audio() {
+    gpio_set_function(AUDIO_PIN, GPIO_FUNC_PWM);
+
+    int audio_pin_slice = pwm_gpio_to_slice_num(AUDIO_PIN);
+
+    // Setup PWM interrupt to fire when PWM cycle is complete
+    pwm_clear_irq(audio_pin_slice);
+    pwm_set_irq_enabled(audio_pin_slice, true);
+
+    // set the handle function above
+    irq_set_exclusive_handler(PWM_IRQ_WRAP, pwm_interrupt_handler);
+    irq_set_enabled(PWM_IRQ_WRAP, true);
+
+    // Setup PWM for audio output
+    pwm_config config = pwm_get_default_config();
+
+    pwm_config_set_clkdiv(&config, AUDIO_CLK_DIV);
+    pwm_config_set_wrap(&config, 250);
+    pwm_init(audio_pin_slice, 0, &config, true);
+
+    pwm_set_gpio_level(AUDIO_PIN, 0);
+}

firmware/src/audio.h

@@ -0,0 +1 @@
+void init_audio();

firmware/src/main.cpp

@@ -4,6 +4,7 @@
 #include "pico/multicore.h"
 #include "hardware/gpio.h"
 #include "mbed_wait_api.h"
+#include "audio.h"
 
 #define Serial Serial1
 
@@ -60,6 +61,8 @@ void setup() {
   Serial.begin(115200);
   Serial.println("Hello worldd!");
 
+
+  init_audio();
   memset(framebuffer, 0, sizeof(framebuffer));
 
   // disable output