Add isConnected method to encoders

src/main/java/com/team766/hal/EncoderReader.java

@@ -12,6 +12,11 @@ enum Type {
      */
     void reset();
 
+    /**
+     * Return true iff the encoder's readings are up-to-date.
+     */
+    boolean isConnected();
+
     /**
      * Get the distance the robot has driven since the last reset.
      *

src/main/java/com/team766/hal/mock/MockEncoder.java

@@ -7,6 +7,7 @@ public class MockEncoder implements EncoderReader {
     private double distance = 0;
     private double rate = 0;
     private double distancePerPulse = 1;
+    private boolean isConnected = false;
 
     public MockEncoder() {}
 
@@ -15,6 +16,11 @@ public void reset() {
         distance = 0;
     }
 
+    @Override
+    public boolean isConnected() {
+        return isConnected;
+    }
+
     @Override
     public double getDistance() {
         return this.distance;
@@ -27,10 +33,16 @@ public double getRate() {
 
     public void setDistance(final double distance_) {
         this.distance = distance_;
+        this.isConnected = true;
     }
 
     public void setRate(final double rate_) {
         this.rate = rate_;
+        this.isConnected = true;
+    }
+
+    public void disconnect() {
+        isConnected = false;
     }
 
     @Override

src/main/java/com/team766/hal/simulator/Encoder.java

@@ -17,6 +17,11 @@ public void reset() {
         set(0);
     }
 
+    @Override
+    public boolean isConnected() {
+        return true;
+    }
+
     @Override
     public double getDistance() {
         int distance = (int) ProgramInterface.encoderChannels[channel].distance;

src/main/java/com/team766/hal/wpilib/CANcoderEncoder.java

@@ -20,6 +20,11 @@ public CANcoderEncoder(int deviceId, String canBus) {
         cancoder = new CANcoder(deviceId, canBus);
     }
 
+    @Override
+    public boolean isConnected() {
+        return cancoder.getPosition().getStatus().isOK();
+    }
+
     @Override
     public double getDistance() {
         StatusSignal<Double> position = cancoder.getPosition();

src/main/java/com/team766/hal/wpilib/Encoder.java

@@ -6,4 +6,9 @@ public class Encoder extends edu.wpi.first.wpilibj.Encoder implements EncoderRea
     public Encoder(final int channelA, final int channelB) {
         super(channelA, channelB);
     }
+
+    @Override
+    public boolean isConnected() {
+        return true;
+    }
 }