examples/Audio_Playback: Update example code.

- Switch to WavReader.
- Fix the handling of multi-channels.
- Simplify the example code.

Signed-off-by: iabdalkader <[email protected]>

Author: iabdalkader

examples/Beginner/Audio_Playback/Audio_Playback.ino

@@ -6,154 +6,84 @@
 */
 
 #include <Arduino_AdvancedAnalog.h>
-
 #include <Arduino_USBHostMbed5.h>
-
 #include <DigitalOut.h>
 #include <FATFileSystem.h>
 
-AdvancedDAC dac1(A12);
-
 USBHostMSD msd;
 mbed::FATFileSystem usb("USB_DRIVE");
 
-FILE * file = nullptr;
-int sample_size = 0;
-int samples_count = 0;
+WavReader wavreader;
+AdvancedDAC dac1(A12);
 
+#define N_SAMPLES   (512)
+int16_t sample_buf[N_SAMPLES];
 
-void setup()
-{
+void setup() {
   Serial.begin(115200);
-  while (!Serial);
+  while (!Serial) {
+  }
 
-  /* Enable power for HOST USB connector. */
+  // Enable power for HOST USB connector.
   pinMode(PA_15, OUTPUT);
   digitalWrite(PA_15, HIGH);
 
-  Serial.println("Please connect a USB stick to the GIGA's USB port ...");
-  while (!msd.connect()) delay(100);
+  Serial.println("Please connect a USB stick to the USB host port ...");
+  while (!msd.connect()) {
+    delay(100);
+  }
 
   Serial.println("Mounting USB device ...");
   int const rc_mount = usb.mount(&msd);
-  if (rc_mount)
-  {
+  if (rc_mount) {
     Serial.print("Error mounting USB device ");
     Serial.println(rc_mount);
-    return;
+    while (1);
   }
 
   Serial.println("Opening audio file ...");
-
-  /* 16-bit PCM Mono 16kHz realigned noise reduction */
-  file = fopen("/USB_DRIVE/AUDIO_SAMPLE.wav", "rb");
-  if (file == nullptr)
-  {
-    Serial.print("Error opening audio file: ");
-    Serial.println(strerror(errno));
-    return;
+  if (!wavreader.open("/USB_DRIVE/AUDIO_SAMPLE.wav")) {
+      Serial.print("Error opening audio file: ");
+      while (1);
   }
 
-  Serial.println("Reading audio header ...");
-  struct wav_header_t
-  {
-    char chunkID[4]; //"RIFF" = 0x46464952
-    unsigned long chunkSize; //28 [+ sizeof(wExtraFormatBytes) + wExtraFormatBytes] + sum(sizeof(chunk.id) + sizeof(chunk.size) + chunk.size)
-    char format[4]; //"WAVE" = 0x45564157
-    char subchunk1ID[4]; //"fmt " = 0x20746D66
-    unsigned long subchunk1Size; //16 [+ sizeof(wExtraFormatBytes) + wExtraFormatBytes]
-    unsigned short audioFormat;
-    unsigned short numChannels;
-    unsigned long sampleRate;
-    unsigned long byteRate;
-    unsigned short blockAlign;
-    unsigned short bitsPerSample;
-  };
-
-  wav_header_t header;
-  fread(&header, sizeof(header), 1, file);
-
-  Serial.println("WAV File Header read:");
   char msg[64] = {0};
-  snprintf(msg, sizeof(msg), "File Type: %s", header.chunkID);
-  Serial.println(msg);
-  snprintf(msg, sizeof(msg), "File Size: %ld", header.chunkSize);
-  Serial.println(msg);
-  snprintf(msg, sizeof(msg), "WAV Marker: %s", header.format);
-  Serial.println(msg);
-  snprintf(msg, sizeof(msg), "Format Name: %s", header.subchunk1ID);
-  Serial.println(msg);
-  snprintf(msg, sizeof(msg), "Format Length: %ld", header.subchunk1Size);
-  Serial.println(msg);
-  snprintf(msg, sizeof(msg), "Format Type: %hd", header.audioFormat);
-  Serial.println(msg);
-  snprintf(msg, sizeof(msg), "Number of Channels: %hd", header.numChannels);
-  Serial.println(msg);
-  snprintf(msg, sizeof(msg), "Sample Rate: %ld", header.sampleRate);
-  Serial.println(msg);
-  snprintf(msg, sizeof(msg), "Sample Rate * Bits/Sample * Channels / 8: %ld", header.byteRate);
-  Serial.println(msg);
-  snprintf(msg, sizeof(msg), "Bits per Sample * Channels / 8: %hd", header.blockAlign);
-  Serial.println(msg);
-  snprintf(msg, sizeof(msg), "Bits per Sample: %hd", header.bitsPerSample);
-  Serial.println(msg);
-
-  /* Find the data section of the WAV file. */
-  struct chunk_t
-  {
-    char ID[4];
-    unsigned long size;
-  };
-
-  chunk_t chunk;
-  snprintf(msg, sizeof(msg), "id\t" "size");
-  Serial.println(msg);
-  /* Find data chunk. */
-  while (true)
-  {
-    fread(&chunk, sizeof(chunk), 1, file);
-    snprintf(msg, sizeof(msg), "%c%c%c%c\t" "%li", chunk.ID[0], chunk.ID[1], chunk.ID[2], chunk.ID[3], chunk.size);
-    Serial.println(msg);
-    if (*(unsigned int *) &chunk.ID == 0x61746164)
-      break;
-    /* Skip chunk data bytes. */
-    fseek(file, chunk.size, SEEK_CUR);
-  }
+  snprintf(msg, sizeof(msg), "Number of Channels: %hd", wavreader.channels()); Serial.println(msg);
+  snprintf(msg, sizeof(msg), "Sample Rate: %ld", wavreader.sample_rate()); Serial.println(msg);
+  snprintf(msg, sizeof(msg), "Bits per Sample: %hd", wavreader.sample_size()); Serial.println(msg);
+  snprintf(msg, sizeof(msg), "Number of Samples = %i", wavreader.sample_count()); Serial.println(msg);
 
-  /* Determine number of samples. */
-  sample_size = header.bitsPerSample / 8;
-  samples_count = chunk.size * 8 / header.bitsPerSample;
-  snprintf(msg, sizeof(msg), "Sample size = %i", sample_size); Serial.println(msg);
-  snprintf(msg, sizeof(msg), "Samples count = %i", samples_count); Serial.println(msg);
+  // Round the total number of samples to a multiple of the DAC's buffer size
+  wavreader.set_max_samples((wavreader.sample_count() / N_SAMPLES) * N_SAMPLES);
 
-  /* Configure the advanced DAC. */
-  if (!dac1.begin(AN_RESOLUTION_12, header.sampleRate, 256, 16))
-  {
+  // Configure and start the DAC. Note that the DAC is single-channel. If the file has two channels,
+  // the buffer size is set to half the number of samples, as the two channels will be averaged.
+  if (!dac1.begin(AN_RESOLUTION_12, wavreader.sample_rate(), N_SAMPLES / wavreader.channels(), 32)) {
     Serial.println("Failed to start DAC1 !");
-    return;
+    while (1);
   }
 }
 
-void loop()
-{
-  if (dac1.available() && !feof(file))
-  {
-    /* Read data from file. */
-    uint16_t sample_data[256] = {0};
-    fread(sample_data, sample_size, 256, file);
-
-    /* Get a free buffer for writing. */
+void loop() {
+  if (dac1.available()) {
+    // Get a free buffer for writing.
     SampleBuffer buf = dac1.dequeue();
 
-    /* Write data to buffer. */
-    for (size_t i = 0; i < buf.size(); i++)
-    {
-      /* Scale down to 12 bit. */
-      uint16_t const dac_val = ((static_cast<unsigned int>(sample_data[i])+32768)>>4) & 0x0fff;
-      buf[i] = dac_val;
+    // Read samples in a loop.
+    wavreader.read(sample_buf, N_SAMPLES, true);
+
+    // Write samples to buffer.
+    for (size_t i=0; i<N_SAMPLES; i+=wavreader.channels()) {
+      // Map the samples to positive range and down scale to 12-bit.
+      if (wavreader.channels() == 1) {
+        buf[i] = ((unsigned int)(sample_buf[i] + 32768)) >> 4;
+      } else {
+        // Average the two channels, if the file has two channels 
+        buf[i / 2] = ((unsigned int)((sample_buf[i] + sample_buf[i+1] / 2) + 32768)) >> 4;
+      }
     }
 
-    /* Write the buffer to DAC. */
+    // Write the buffer to DAC.
     dac1.write(buf);
   }
 }