Polar parser

MyTracks/src/com/google/android/apps/mytracks/services/sensors/PolarMessageParser.java

@@ -0,0 +1,130 @@
+/*
+ * Copyright 2011 Google Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License"); you may not
+ * use this file except in compliance with the License. You may obtain a copy of
+ * the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+ * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+ * License for the specific language governing permissions and limitations under
+ * the License.
+ */
+package com.google.android.apps.mytracks.services.sensors;
+
+import android.util.Log;
+
+import com.google.android.apps.mytracks.Constants;
+import com.google.android.apps.mytracks.content.Sensor;
+
+/**
+ * An implementation of a SensorData parser for Polar Wearlink Bluetooth HRM.
+ *
+ * @author John R. Gerthoffer
+ */
+public class PolarMessageParser implements MessageParser {
+  // Last Heart Rate value storage (in case of corrupt buffer)
+  private int lastHeartRate = 0;                   
+  
+  @Override
+  public Sensor.SensorDataSet parseBuffer(byte[] buffer) {
+    StringBuilder sb = new StringBuilder();
+    int heartRate = 0;
+    
+    // Due to a memory inconsistency issue, the packet does not always start at buffer[0].
+    // While it works stepping thru in debug mode, it is not consistent when running real-time.
+    // Note: After changing the BluetoothConnectionManager to pass a copy of 'buffer', 
+    //       the problem was resolved!  Passing a buffer copy in threaded comm's is typical in my experience.  
+
+    // Minimum length Polar packets is 8, so stop search 8 bytes before buffer ends.
+    heartRate = lastHeartRate;                          // Default to use last value. (If our buffer is corrupted).
+    for (int i = 0; i < buffer.length - 8; i++) {
+      boolean bHdrOK = ((buffer[i] & 0xFF) == 0xFE); 
+      boolean bChkOK = ((buffer[i+2] & 0xFF) == (0xFF - (buffer[i+1] & 0xFF))); 
+      boolean bSeqOK = ((buffer[i+3] & 0xFF) < 16); 
+      boolean bStatusOK = ((buffer[i+4] & 0xFF) > 128); // I've seen 0xF1 or 0xE1. 
+
+      if (bHdrOK && bChkOK && bSeqOK && bStatusOK) {
+        heartRate = buffer[i + 5] & 0xFF;
+        lastHeartRate = heartRate;                      // Remember good value for next time.
+        break;						                    // Let's go store our data.  
+      }
+    }
+
+    // Heart Rate
+    Sensor.SensorData.Builder b = Sensor.SensorData.newBuilder()
+      .setValue(heartRate)
+      .setState(Sensor.SensorState.SENDING);
+
+    Sensor.SensorDataSet sds =
+      Sensor.SensorDataSet.newBuilder()
+      .setCreationTime(System.currentTimeMillis())
+      .setHeartRate(b)
+      .build();
+    
+    return sds;
+  }
+
+  /**
+   * Applies packet validation rule to buffer
+   * Parsing rule for a good Polar HRM packet;
+   *   boolean goodHdr = ((buffer[0] & 0xFF) == 0xFE);
+   *   boolean goodChk = ((buffer[2] & 0xFF) == (0xFF - (buffer[1] & 0xFF)));
+   *   goodPacket = goodHdr && goodChk;
+   *     
+   * @param an array of bytes to parse
+   * @return whether buffer has a valid packet starting at index zero
+   */
+  @Override
+  public boolean isValid(byte[] buffer) {
+	/**
+	 *  Polar Bluetooth Wearlink packet example;
+	 *   Hdr Len Chk Seq Status HeartRate RRInterval_16-bits
+     *    FE  08  F7  06   F1      48          03 64
+     *   where Hdr always = 0xFE, Chk = 0xFF - Len
+     *               
+     *  Additional packet examples;
+     *    FE 08 F7 06 F1 48 03 64           
+     *    FE 0A F5 06 F1 48 03 64 03 70
+	 */
+    boolean goodHdr = ((buffer[0] & 0xFF) == 0xFE);
+    boolean goodChk = ((buffer[2] & 0xFF) == (0xFF - (buffer[1] & 0xFF)));
+    return goodHdr && goodChk;    
+  }
+
+  /**
+   * Polar uses variable packet sizes; 8, 10, 12, 14 and rarely 16.
+   * The most frequent are 8 and 10.
+   * We will wait for 16 bytes.
+   * This way, we are assured of getting one good one.
+   * 
+   * @return the size of buffer needed to parse a good packet
+   */
+  @Override
+  public int getFrameSize() {
+	return 16;									
+  }
+
+  /**
+   * Searches buffer for the beginning of a valid packet.
+   * Parsing rule for a good Polar HRM packet;
+   *   boolean goodHdr = ((buffer[0] & 0xFF) == 0xFE);
+   *   boolean goodChk = ((buffer[2] & 0xFF) == (0xFF - (buffer[1] & 0xFF)));
+   *   goodPacket = goodHdr && goodChk;
+   *     
+   * @param an array of bytes to parse
+   */
+  @Override
+  public int findNextAlignment(byte[] buffer) {
+    // Minimum length Polar packets is 8, so stop search 8 bytes before buffer ends.
+    for (int i = 0; i < buffer.length - 8; i++) {
+      if (((buffer[i] & 0xFF) == 0xFE) && ((buffer[i+2] & 0xFF) == (0xFF - (buffer[i+1] & 0xFF)))) {
+	    return i;
+      }
+    }
+    return -1;
+  }
+}