PDM: use SAMD I2S style double buffer, without nrfx, add plotter example (#1)

* PDM: use SAMD I2S style double buffer, without nrfx, add plotter example

Co-Authored-By: per1234 <accounts@perglass.com>

Author: 2 people

libraries/PDM/examples/PDMSerialPlotter/PDMSerialPlotter.ino

@@ -0,0 +1,62 @@
+/*
+  This example reads audio data from the on-board PDM microphones, and prints
+  out the samples to the Serial console. The Serial Plotter built into the
+  Arduino IDE can be used to plot the audio data (Tools -> Serial Plotter)
+
+  Circuit:
+  - Arduino Nano 33 BLE board
+
+  This example code is in the public domain.
+*/
+
+#include <PDM.h>
+
+// buffer to read samples into, each sample is 16-bits
+short sampleBuffer[256];
+
+// number of samples read
+volatile int samplesRead;
+
+void setup() {
+  Serial.begin(9600);
+  while (!Serial);
+
+  // configure the data receive callback
+  PDM.onReceive(onPDMdata);
+
+  // optionally set the gain, defaults to 20
+  // PDM.setGain(30);
+
+  // initialize PDM with:
+  // - one channel (mono mode)
+  // - a 16 kHz sample rate
+  if (!PDM.begin(1, 16000)) {
+    Serial.println("Failed to start PDM!");
+    while (1);
+  }
+}
+
+void loop() {
+  // wait for samples to be read
+  if (samplesRead) {
+
+    // print samples to the serial monitor or plotter
+    for (int i = 0; i < samplesRead; i++) {
+      Serial.println(sampleBuffer[i]);
+    }
+
+    // clear the read count
+    samplesRead = 0;
+  }
+}
+
+void onPDMdata() {
+  // query the number of bytes available
+  int bytesAvailable = PDM.available();
+
+  // read into the sample buffer
+  PDM.read(sampleBuffer, bytesAvailable);
+
+  // 16-bit, 2 bytes per sample
+  samplesRead = bytesAvailable / 2;
+}

libraries/PDM/examples/RecordAndDumpOnSerial/RecordAndDumpOnSerial.ino

@@ -14,8 +14,12 @@ PDM	KEYWORD1
 begin	KEYWORD2
 end	KEYWORD2
 
+available	KEYWORD2
+read	KEYWORD2
+
 onReceive	KEYWORD2
 
+setGain	KEYWORD2
 setBufferSize	KEYWORD2
 
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