BLE - Add CordioHCIDriver::on_host_stack_inactivity

This callback should be called by the host stack when it has no pending activities. It allows a driver to put its controller to sleep.

features/FEATURE_BLE/targets/TARGET_CORDIO/driver/CordioHCIDriver.cpp

@@ -283,6 +283,10 @@ uint16_t CordioHCIDriver::write(uint8_t type, uint16_t len, uint8_t *pData)
     return _transport_driver.write(type, len, pData);
 }
 
+void CordioHCIDriver::on_host_stack_inactivity()
+{
+}
+
 } // namespace cordio
 } // namespace vendor
 } // namespace ble

features/FEATURE_BLE/targets/TARGET_CORDIO/driver/CordioHCIDriver.h

@@ -134,6 +134,16 @@ public:
      */
     uint16_t write(uint8_t type, uint16_t len, uint8_t *pData);
 
+    /**
+     * React to host stack inactivity.
+     *
+     * The host stack invoke this function when it is inactive. It allows a
+     * driver to put its controller to sleep if all the conditions are met.
+     *
+     * Any call to write signals to the driver that the host stack is active.
+     */
+     virtual void on_host_stack_inactivity();
+
 protected:
     /**
      * Return a default set of memory pool that the Cordio stack can use.