- new method to calculate an Int from Little Endian data (according to the HxM documentation the data is Little Endian)

- new methods to calculate the CRC8 checksum
- in ZephyrMessageParser the CRC8 now is used in isValid() and the cadence and power values are written to the SensorData objects

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

@@ -24,6 +24,7 @@ import com.google.android.maps.mytracks.R;
  * A collection of methods for message parsers.
  *
  * @author Sandor Dornbush
+ * @author Nico Laum
  */
 public class SensorUtils {
 
@@ -41,7 +42,52 @@ public class SensorUtils {
     r |= buffer[index + 1] & 0xFF;
     return r;
   }
-
+  
+  /**
+   * Extract one unsigned short from a little endian byte array.
+   * @param buffer the buffer to extract the short from
+   * @param index the first byte to be interpreted as part of the short
+   * @return The unsigned short at the given index in the buffer
+   */
+	public static int unsignedShortToIntLittleEndian(byte[] buffer, int index) {
+		int r = buffer[index] & 0xFF;
+		r |= (buffer[index + 1] & 0xFF) << 8;
+		return r;
+	}
+	
+	/**
+	 * Returns CRC8 (polynomial 0x8C) from byte array buffer[start] until (including) buffer[end]
+	 * @param buffer the byte array of data (payload)
+	 * @param start the position in the byte array where the payload begins
+	 * @param end the position in the byte array where the payload ends
+	 * @return CRC8 value
+	 */
+	public static int getCrc8(byte[] buffer, int start, int end) {
+		int[] crc = { 0x0 };
+		
+		for (int i = start; i < (end+1); i++) {
+			crc8PushByte(crc, buffer[i]);
+		}
+		return crc[0];
+	}
+	
+	/**
+	 * Updates a CRC8 value by using the next byte passed to this method
+	 * @param crc int of crc value (as an array to pass it as reference)
+	 * @param add the next byte to add to the CRC8 calculation
+	 */
+	private static void crc8PushByte(int[] crc, byte add) {
+		int addInt = (add & 0x000000FF);
+		crc[0] = crc[0] ^ addInt;
+		for (int i = 0; i < 8; i++) {
+			if ((crc[0] & 0x00000001) != 0x00000000) {
+				crc[0] = (crc[0] >> 1) ^ 0x0000008C;
+			} else {
+				crc[0] = (crc[0] >> 1);
+			}
+		}
+	}
+	
   public static String getStateAsString(Sensor.SensorState state, Context c) {
     switch (state) {
       case NONE:

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

@@ -27,7 +27,6 @@ import com.google.android.apps.mytracks.content.Sensor;
  */
 public class ZephyrMessageParser implements MessageParser {
 
-  @Override
   public Sensor.SensorDataSet parseBuffer(byte[] buffer) {
     StringBuilder sb = new StringBuilder();
     for (int i = 0; i < buffer.length; i++) {
@@ -35,36 +34,42 @@ public class ZephyrMessageParser implements MessageParser {
     }
     Log.w(Constants.TAG, "Got zephyr data: " + sb);
     // The provided units are 1/16 strides per minute.
-    // TODO: Fix the cadence calculation.
-    // int cadence = SensorUtils.unsignedShortToInt(buffer, 56);
     // Heart Rate
-    Sensor.SensorData.Builder b = Sensor.SensorData.newBuilder()
-      .setValue(buffer[12] & 0xFF)
-      .setState(Sensor.SensorState.SENDING);
+    Sensor.SensorData.Builder heartrate = Sensor.SensorData.newBuilder()
+    .setValue(buffer[12] & 0xFF)
+    .setState(Sensor.SensorState.SENDING);
+    // Changes Nico Laum (Power and Cadence)
+    Sensor.SensorData.Builder power = Sensor.SensorData.newBuilder()
+	    .setValue(buffer[11] & 0xFF)
+	    .setState(Sensor.SensorState.SENDING);
+    Sensor.SensorData.Builder cadence = Sensor.SensorData.newBuilder()
+	    .setValue(SensorUtils.unsignedShortToIntLittleEndian(buffer, 56)/16)
+	    .setState(Sensor.SensorState.SENDING);
+    
       // Cadence
       //.setCadence(cadence / 16)
       //.build();
     Sensor.SensorDataSet sds =
       Sensor.SensorDataSet.newBuilder()
       .setCreationTime(System.currentTimeMillis())
-      .setHeartRate(b)
+      .setPower(power)
+      .setHeartRate(heartrate)
+      .setCadence(cadence)
       .build();
     
     return sds;
   }
 
-  @Override
   public boolean isValid(byte[] buffer) {
-    // TODO crc etc.
-    return buffer[0] == 0x02 && buffer[59] == 0x03;
+	  // Changes Nico Laum
+	  // Check STX, ETX and CRC Checksum
+    return (buffer[0] == 0x02 && buffer[59] == 0x03 && (SensorUtils.getCrc8(buffer, 3, 57) == (int) (buffer[58] & 0xFF)));
   }
 
-  @Override
   public int getFrameSize() {
     return 60;
   }
 
-  @Override
   public int findNextAlignment(byte[] buffer) {
     // TODO test or understand this code.
     for (int i = 0; i < buffer.length - 1; i++) {