uart: add function mraa_uart_get_dev_path

Used for getting the path to the character device under linux for uart
device. i.e. "/dev/ttyS0"

Adds paths to existing platforms.
Closes #84

Signed-off-by: Thomas Ingleby <thomas.c.ingleby@intel.com>

api/mraa/common.h

@@ -149,6 +149,7 @@ typedef struct {
     unsigned int index; /**< ID as exposed in the system */
     int rx; /**< uart rx */
     int tx; /**< uart tx */
+    char* device_path; /**< To store "/dev/ttyS1" for example */
     /*@}*/
 } mraa_uart_dev_t;
 

api/mraa/uart.h

@@ -54,6 +54,15 @@ typedef struct _uart* mraa_uart_context;
  */
 mraa_uart_context mraa_uart_init(int uart);
 
+/**
+ * Get Char pointer with tty device path within Linux
+ * For example. Could point to "/dev/ttyS0"
+ *
+ * @param dev uart context
+ * @return char pointer of device path
+ */
+char* mraa_uart_get_dev_path(mraa_uart_context dev);
+
 #ifdef __cplusplus
 }
 #endif

api/mraa/uart.hpp

@@ -55,6 +55,17 @@ class Uart {
         ~Uart() {
             return;
         }
+
+        /**
+         * Get string with tty device path within Linux
+         * For example. Could point to "/dev/ttyS0"
+         *
+         * @return char pointer of device path
+         */
+        std::string getDevicePath() {
+            std::string ret_val(mraa_uart_get_dev_path(m_uart));
+            return ret_val;
+        }
     private:
         mraa_uart_context m_uart;
 };