Add PDM library for Arduino Nano RP2040 Connect (#213)

* Add PDM library for Arduino Nano RP2040 Connect

* No PDM test in CI, only works on Arduino Nano RP2040

libraries/PDM/examples/PDMSerialPlotter/PDMSerialPlotter.ino

@@ -0,0 +1,83 @@
+/*
+  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, or
+  - Arduino Nano RP2040 Connect, or
+  - Arduino Portenta H7 board plus Portenta Vision Shield
+
+  This example code is in the public domain.
+*/
+
+#include <PDM.h>
+
+// default number of output channels
+static const char channels = 1;
+
+// default PCM output frequency
+static const int frequency = 16000;
+
+// Buffer to read samples into, each sample is 16-bits
+short sampleBuffer[512];
+
+// Number of audio 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 on the BLE Sense and -10 on the Portenta Vision Shield
+  // PDM.setGain(30);
+
+  // Initialize PDM with:
+  // - one channel (mono mode)
+  // - a 16 kHz sample rate for the Arduino Nano 33 BLE Sense
+  // - a 32 kHz or 64 kHz sample rate for the Arduino Portenta Vision Shield
+  if (!PDM.begin(channels, frequency)) {
+    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++) {
+      if(channels == 2) {
+        Serial.print("L:");
+        Serial.print(sampleBuffer[i]);
+        Serial.print(" R:");
+        i++;
+      }
+      Serial.println(sampleBuffer[i]);
+    }
+
+    // Clear the read count
+    samplesRead = 0;
+  }
+}
+
+/**
+ * Callback function to process the data from the PDM microphone.
+ * NOTE: This callback is executed as part of an ISR.
+ * Therefore using `Serial` to print messages inside this function isn't supported.
+ * */
+void onPDMdata() {
+  // Query the number of available bytes
+  int bytesAvailable = PDM.available();
+
+  // Read into the sample buffer
+  PDM.read(sampleBuffer, bytesAvailable);
+
+  // 16-bit, 2 bytes per sample
+  samplesRead = bytesAvailable / 2;
+}

libraries/PDM/keywords.txt

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+#######################################
+# Syntax Coloring Map PDM
+#######################################
+
+#######################################
+# Datatypes (KEYWORD1)
+#######################################
+
+PDM	KEYWORD1
+
+#######################################
+# Methods and Functions (KEYWORD2)
+#######################################
+begin	KEYWORD2
+end	KEYWORD2
+
+available	KEYWORD2
+read	KEYWORD2
+
+onReceive	KEYWORD2
+
+setGain	KEYWORD2
+setBufferSize	KEYWORD2
+
+#######################################
+# Constants (LITERAL1)
+#######################################

libraries/PDM/library.properties

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+name=PDM
+version=1.0
+author=Arduino
+maintainer=Arduino <[email protected]>
+sentence=Enables the communication with devices that use the PDM Bus. Specific implementation for nRF52.
+paragraph=
+category=Communication
+url=
+architectures=rp2040

libraries/PDM/src/PDM.h

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+/*
+  Copyright (c) 2019 Arduino LLC.  All right reserved.
+
+  This library is free software; you can redistribute it and/or
+  modify it under the terms of the GNU Lesser General Public
+  License as published by the Free Software Foundation; either
+  version 2.1 of the License, or (at your option) any later version.
+
+  This library is distributed in the hope that it will be useful,
+  but WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+  See the GNU Lesser General Public License for more details.
+
+  You should have received a copy of the GNU Lesser General Public
+  License along with this library; if not, write to the Free Software
+  Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
+*/
+
+#ifndef _PDM_H_INCLUDED
+#define _PDM_H_INCLUDED
+
+#include <Arduino.h>
+//#include <pinDefinitions.h>
+
+#include "utility/PDMDoubleBuffer.h"
+
+class PDMClass
+{
+public:
+  PDMClass(int dinPin, int clkPin, int pwrPin);
+  virtual ~PDMClass();
+
+  int begin(int channels, int sampleRate);
+  void end();
+
+  virtual int available();
+  virtual int read(void* buffer, size_t size);
+
+  void onReceive(void(*)(void));
+
+  //PORTENTA_H7 min -12 max 51
+  //NANO 33 BLE SENSe min 0 max 80
+  void setGain(int gain);
+  void setBufferSize(int bufferSize);
+  size_t getBufferSize();
+
+// private:
+  void IrqHandler(bool halftranfer);
+
+private:
+  int _dinPin;
+  int _clkPin;
+  int _pwrPin;
+
+  int _channels;
+  int _samplerate;
+
+  int _gain;
+  int _init;
+
+  PDMDoubleBuffer _doubleBuffer;
+
+  void (*_onReceive)(void);
+};
+#ifdef PIN_PDM_DIN
+extern PDMClass PDM;
+#endif
+#endif