Make I2c polling on the MCP23017 IO expander dynamic

I've experienced that polling the MCP23017 IO expander on a 50ms base is
not really needed.  Therefore, I propose to make the polling time
dynamic, with a default of 50ms.  This way, people who don't want to
change this, can use the SW the way they used it before.  Others can put
the polling time to a value of their preference.

pi4j-gpio-extension/src/main/java/com/pi4j/gpio/extension/mcp/MCP23017GpioProvider.java

@@ -61,6 +61,7 @@ public class MCP23017GpioProvider extends GpioProviderBase implements GpioProvid
  public static final String NAME = "com.pi4j.gpio.extension.mcp.MCP23017GpioProvider";
  public static final String DESCRIPTION = "MCP23017 GPIO Provider";
  public static final int DEFAULT_ADDRESS = 0x20;
+ public static final int DEFAULT_POLLING_TIME = 50;
 
  private static final int REGISTER_IODIR_A = 0x00;
  private static final int REGISTER_IODIR_B = 0x01;
@@ -89,18 +90,28 @@ public class MCP23017GpioProvider extends GpioProviderBase implements GpioProvid
  private int currentPullupA = 0;
  private int currentPullupB = 0;
 
+ private int pollingTime = DEFAULT_POLLING_TIME;
+
  private boolean i2cBusOwner = false;
  private final I2CBus bus;
  private final I2CDevice device;
  private GpioStateMonitor monitor = null;
 
  public MCP23017GpioProvider(int busNumber, int address) throws IOException {
  // create I2C communications bus instance
- this(I2CFactory.getInstance(busNumber), address);
- i2cBusOwner = true;
+ this(busNumber, address, DEFAULT_POLLING_TIME);
+ }
+
+ public MCP23017GpioProvider(int busNumber, int address, int pollingTime) throws IOException {
+ // create I2C communications bus instance
+ this(I2CFactory.getInstance(busNumber), address, pollingTime);
  }
 
  public MCP23017GpioProvider(I2CBus bus, int address) throws IOException {
+ this(bus, address, DEFAULT_POLLING_TIME);
+ }
+
+ public MCP23017GpioProvider(I2CBus bus, int address, int pollingTime) throws IOException {
 
  // set reference to I2C communications bus instance
  this.bus = bus;
@@ -135,6 +146,11 @@ public MCP23017GpioProvider(I2CBus bus, int address) throws IOException {
  // set all default pin pull up resistors
  device.write(REGISTER_GPPU_A, (byte) currentPullupA);
  device.write(REGISTER_GPPU_B, (byte) currentPullupB);
+
+ // set pollingtime
+ this.pollingTime = pollingTime;
+
+ i2cBusOwner = true;
  }
 
  @Override
@@ -408,6 +424,9 @@ public void shutdown() {
  }
  }
 
+ public void setPollingTime(int pollingTime) {
+ this.pollingTime = pollingTime;
+ }
 
  /**
  * This class/thread is used to to actively monitor for GPIO interrupts
@@ -481,7 +500,7 @@ public void run() {
 
  // ... lets take a short breather ...
  Thread.currentThread();
- Thread.sleep(50);
+ Thread.sleep(pollingTime);
  } catch (Exception ex) {
  ex.printStackTrace();
  }