Added reset recovery for I2C

Hardware Reset API should do the recovery of I2C bus,
but in absence of reset pin connected to slave device we need
software recovery of I2C bus.

drivers/I2C.cpp

@@ -13,7 +13,10 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
+
 #include "drivers/I2C.h"
+#include "drivers/DigitalInOut.h"
+#include "platform/mbed_wait_api.h"
 
 #if DEVICE_I2C
 
@@ -32,13 +35,15 @@ I2C::I2C(PinName sda, PinName scl) :
 #endif
     _i2c(), _hz(100000)
 {
-    // No lock needed in the constructor
-
+    lock();
     // The init function also set the frequency to 100000
-    i2c_init(&_i2c, sda, scl);
-
+    _sda = sda;
+    _scl = scl;
+    recover(sda, scl);
+    i2c_init(&_i2c, _sda, _scl);
     // Used to avoid unnecessary frequency updates
     _owner = this;
+    unlock();
 }
 
 void I2C::frequency(int hz)
@@ -135,6 +140,53 @@ void I2C::unlock()
     _mutex->unlock();
 }
 
+int I2C::recover(PinName sda, PinName scl)
+{
+    DigitalInOut pin_sda(sda, PIN_INPUT, PullNone, 1);
+    DigitalInOut pin_scl(scl, PIN_INPUT, PullNone, 1);
+
+    // Read and verify if recovery is required
+    if (pin_scl == 1) {
+        if (pin_sda == 1) {
+            // Return successfuly as SDA and SCL is high
+            return 0;
+        }
+    } else {
+        // Return as SCL is low and no access to become master.
+        return I2C_ERROR_BUS_BUSY;
+    }
+
+    // Send clock pulses, for device to recover 9
+    pin_scl.mode(PullNone);
+    pin_scl.output();
+    int count = 9;
+    while (count--) {
+        pin_scl.mode(PullNone);
+        pin_scl = 0;
+        wait_us(5);
+        pin_scl.mode(PullUp);
+        pin_scl = 1;
+        wait_us(5);
+    }
+
+    // Send Stop
+    pin_sda.output();
+    pin_sda = 0;
+    wait_us(5);
+    pin_scl = 1;
+    wait_us(5);
+    pin_sda = 1;
+    wait_us(5);
+
+    pin_sda.input();
+    pin_scl.input();
+    if ((pin_scl == 0) || (pin_sda == 0)) {
+        // Return as SCL is low and no access to become master.
+        return I2C_ERROR_BUS_BUSY;
+    }
+    return 0;
+}
+
 #if DEVICE_I2C_ASYNCH
 
 int I2C::transfer(int address, const char *tx_buffer, int tx_length, char *rx_buffer, int rx_length, const event_callback_t &callback, int event, bool repeated)
@@ -169,10 +221,10 @@ void I2C::irq_handler_asynch(void)
     if (_callback && event) {
         _callback.call(event);
     }
+
     if (event) {
         unlock_deep_sleep();
     }
-
 }
 
 void I2C::lock_deep_sleep()

drivers/I2C.h

@@ -17,6 +17,7 @@
 #define MBED_I2C_H
 
 #include "platform/platform.h"
+#include "hal/gpio_api.h"
 
 #if defined (DEVICE_I2C) || defined(DOXYGEN_ONLY)
 
@@ -197,8 +198,24 @@ protected:
 
     i2c_t _i2c;
     static I2C  *_owner;
-    int         _hz;
+    int    _hz;
     static SingletonPtr<PlatformMutex> _mutex;
+    PinName _sda;
+    PinName _scl;
+
+private:
+    /** Recover I2C bus, when stuck with SDA low
+     *  @note : Initialization of I2C bus is required after this API.
+     *
+     *  @param sda I2C data line pin
+     *  @param scl I2C clock line pin
+     *
+     * @returns:
+     *    '0' - Successfully recovered
+     *    'I2C_ERROR_BUS_BUSY' - In case of failure
+     *
+     */
+    int recover(PinName sda, PinName scl);
 };
 
 } // namespace mbed