i2c: Add functions for bulk read from register

Functions issue a write command for the register to read from and then a read
command without a stop signal in between

Signed-off-by: Gabriel Smith <ga29smith@gmail.com>
Signed-off-by: Brendan Le Foll <brendan.le.foll@intel.com>

api/mraa/i2c.h

@@ -115,6 +115,17 @@ uint8_t mraa_i2c_read_byte_data(mraa_i2c_context dev, const uint8_t command);
  */
 uint16_t mraa_i2c_read_word_data(mraa_i2c_context dev, const uint8_t command);
 
+/**
+ * Bulk read from i2c context, starting from designated register
+ *
+ * @param dev The i2c context
+ * @param command The register
+ * @param data pointer to the byte array to read data in to
+ * @param length max number of bytes to read
+ * @return The length in bytes passed to the function or 0
+ */
+int mraa_i2c_read_bytes_data(mraa_i2c_context dev, uint8_t command, uint8_t* data, int length);
+
 /**
  * Write length bytes to the bus, the first byte in the array is the
  * command/register to write

api/mraa/i2c.hpp

@@ -132,6 +132,19 @@ class I2c {
             return mraa_i2c_read_word_data(m_i2c, reg);
         }
 
+        /**
+         * Read length bytes from the bus into *data pointer starting from
+         * an i2c register
+         *
+         * @param reg Register to read from
+         * @param data pointer to the byte array to read data in to
+         * @param length max number of bytes to read
+         * @return length passed to the function or 0
+         */
+        int readBytesReg(uint8_t reg, uint8_t* data, int length) {
+            return mraa_i2c_read_bytes_data(m_i2c, reg, data, length);
+        }
+
         /**
          * Write a byte on the bus
          *