Fix-up Zephyr

- Add cadence
- Add power
- Check crc

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 {
 
@@ -32,6 +33,7 @@ public class SensorUtils {
 
   /**
    * Extract one unsigned short from a big 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
@@ -42,6 +44,56 @@ public class SensorUtils {
     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++) {
+      crc = crc8PushByte(crc, buffer[i]);
+    }
+    return crc;
+  }
+
+  /**
+   * Updates a CRC8 value by using the next byte passed to this method
+   * 
+   * @param crc int of crc value
+   * @param add the next byte to add to the CRC8 calculation
+   */
+  private static int crc8PushByte(int crc, byte add) {
+    int addInt = (add & 0x000000FF);
+    crc = crc ^ addInt;
+    for (int i = 0; i < 8; i++) {
+      if ((crc & 0x00000001) != 0x00000000) {
+        crc = (crc >> 1) ^ 0x0000008C;
+      } else {
+        crc = (crc >> 1);
+      }
+    }
+    return crc;
+  }
+	
   public static String getStateAsString(Sensor.SensorState state, Context c) {
     switch (state) {
       case NONE:

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

@@ -21,7 +21,7 @@ import com.google.android.apps.mytracks.Constants;
 import com.google.android.apps.mytracks.content.Sensor;
 
 /**
- * An implementation of a SensorData parser for Zephyr HRM.
+ * An implementation of a Sensor MessageParser for Zephyr.
  *
  * @author Sandor Dornbush
  */
@@ -34,20 +34,24 @@ public class ZephyrMessageParser implements MessageParser {
       sb.append(String.format("%02X", buffer[i]));
     }
     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);
-      // Cadence
-      //.setCadence(cadence / 16)
-      //.build();
+    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);
+    
     Sensor.SensorDataSet sds =
       Sensor.SensorDataSet.newBuilder()
       .setCreationTime(System.currentTimeMillis())
-      .setHeartRate(b)
+      .setPower(power)
+      .setHeartRate(heartrate)
+      .setCadence(cadence)
       .build();
     
     return sds;
@@ -55,8 +59,10 @@ public class ZephyrMessageParser implements MessageParser {
 
   @Override
   public boolean isValid(byte[] buffer) {
-    // TODO crc etc.
-    return buffer[0] == 0x02 && buffer[59] == 0x03;
+    // Check STX, ETX and CRC Checksum
+    return buffer[0] == 0x02
+        && buffer[59] == 0x03
+        && SensorUtils.getCrc8(buffer, 3, 57) == (int) (buffer[58] & 0xFF);
   }
 
   @Override