AP_HAL_Empty: add semaphore to I2CDriver

libraries/AP_HAL_Empty/HAL_Empty_Class.cpp

@@ -10,7 +10,8 @@ using namespace Empty;
 static EmptyUARTDriver uartADriver;
 static EmptyUARTDriver uartBDriver;
 static EmptyUARTDriver uartCDriver;
-static EmptyI2CDriver  i2cDriver;
+static EmptySemaphore  i2cSemaphore;
+static EmptyI2CDriver  i2cDriver(&i2cSemaphore);
 static EmptySPIDeviceManager spiDeviceManager;
 static EmptyAnalogIn analogIn;
 static EmptyStorage storageDriver;

libraries/AP_HAL_Empty/I2CDriver.h

@@ -6,6 +6,7 @@
 
 class Empty::EmptyI2CDriver : public AP_HAL::I2CDriver {
 public:
+    EmptyI2CDriver(AP_HAL::Semaphore* semaphore) : _semaphore(semaphore) {}
     void begin();
     void end();
     void setTimeout(uint16_t ms);
@@ -31,6 +32,10 @@ public:
 
     uint8_t lockup_count();
 
+    AP_HAL::Semaphore* get_semaphore() { return _semaphore; }
+
+private:
+    AP_HAL::Semaphore* _semaphore;
 };
 
 #endif // __AP_HAL_EMPTY_I2CDRIVER_H__