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+// MPU-6050 Accelerometer + Gyro
+// -----------------------------
+//
+// By arduino.cc user "Krodal".
+// June 2012
+// Open Source / Public Domain
+//
+// Using Arduino 1.0.1
+// It will not work with an older version,
+// since Wire.endTransmission() uses a parameter
+// to hold or release the I2C bus.
+//
+// Documentation:
+// - The InvenSense documents:
+//   - "MPU-6000 and MPU-6050 Product Specification",
+//     PS-MPU-6000A.pdf
+//   - "MPU-6000 and MPU-6050 Register Map and Descriptions",
+//     RM-MPU-6000A.pdf or RS-MPU-6000A.pdf
+//   - "MPU-6000/MPU-6050 9-Axis Evaluation Board User Guide"
+//     AN-MPU-6000EVB.pdf
+//
+// The accuracy is 16-bits.
+//
+// Temperature sensor from -40 to +85 degrees Celsius
+//   340 per degrees, -512 at 35 degrees.
+//
+// At power-up, all registers are zero, except these two:
+//      Register 0x6B (PWR_MGMT_2) = 0x40  (I read zero).
+//      Register 0x75 (WHO_AM_I)   = 0x68.
+//
+
+#include "MPU6050.h"
+
+// --------------------------------------------------------
+// MPU6050_read
+//
+// This is a common function to read multiple bytes
+// from an I2C device.
+//
+// It uses the boolean parameter for Wire.endTransMission()
+// to be able to hold or release the I2C-bus.
+// This is implemented in Arduino 1.0.1.
+//
+// Only this function is used to read.
+// There is no function for a single byte.
+//
+int MPU6050_read(int start, uint8_t *buffer, int size)
+{
+  int i, n, error;
+
+  Wire.beginTransmission(MPU6050_I2C_ADDRESS);
+  n = Wire.write(start);
+  if (n != 1)
+    return (-10);
+
+  n = Wire.endTransmission(false);    // hold the I2C-bus
+  if (n != 0)
+    return (n);
+
+  // Third parameter is true: relase I2C-bus after data is read.
+  Wire.requestFrom(MPU6050_I2C_ADDRESS, size, true);
+  i = 0;
+  while(Wire.available() && i<size)
+  {
+    buffer[i++]=Wire.read();
+  }
+  if ( i != size)
+    return (-11);
+
+  return (0);  // return : no error
+}
+
+
+// --------------------------------------------------------
+// MPU6050_write
+//
+// This is a common function to write multiple bytes to an I2C device.
+//
+// If only a single register is written,
+// use the function MPU_6050_write_reg().
+//
+// Parameters:
+//   start : Start address, use a define for the register
+//   pData : A pointer to the data to write.
+//   size  : The number of bytes to write.
+//
+// If only a single register is written, a pointer
+// to the data has to be used, and the size is
+// a single byte:
+//   int data = 0;        // the data to write
+//   MPU6050_write (MPU6050_PWR_MGMT_1, &c, 1);
+//
+int MPU6050_write(int start, const uint8_t *pData, int size)
+{
+  int n, error;
+
+  Wire.beginTransmission(MPU6050_I2C_ADDRESS);
+  n = Wire.write(start);        // write the start address
+  if (n != 1)
+    return (-20);
+
+  n = Wire.write(pData, size);  // write data bytes
+  if (n != size)
+    return (-21);
+
+  error = Wire.endTransmission(true); // release the I2C-bus
+  if (error != 0)
+    return (error);
+
+  return (0);         // return : no error
+}
+
+// --------------------------------------------------------
+// MPU6050_write_reg
+//
+// An extra function to write a single register.
+// It is just a wrapper around the MPU_6050_write()
+// function, and it is only a convenient function
+// to make it easier to write a single register.
+//
+int MPU6050_write_reg(int reg, uint8_t data)
+{
+  int error;
+
+  error = MPU6050_write(reg, &data, 1);
+
+  return (error);
+}
+
+// --------------------------------------------------------
+// MPU6050_init
+//
+// Initialization
+//
+int MPU6050_init()
+{
+        // default at power-up:
+    //    Gyro at 250 degrees second
+    //    Acceleration at 2g
+    //    Clock source at internal 8MHz
+    //    The device is in sleep mode.
+    //
+    uint8_t c;
+    int error;
+    error = MPU6050_read (MPU6050_WHO_AM_I, &c, 1);
+    if (error) return error;
+
+    // According to the datasheet, the 'sleep' bit
+    // should read a '1'. But I read a '0'.
+    // That bit has to be cleared, since the sensor
+    // is in sleep mode at power-up. Even if the
+    // bit reads '0'.
+    error = MPU6050_read (MPU6050_PWR_MGMT_2, &c, 1);
+    if (error) return error;
+
+    // Clear the 'sleep' bit to start the sensor.
+    MPU6050_write_reg (MPU6050_PWR_MGMT_1, 0);
+    return 0;
+}
+
+// --------------------------------------------------------
+// MPU6050_readout
+//
+// Perform an complete read-out
+//
+
+int MPU6050_readout(accel_t_gyro_union* accel_t_gyro)
+{
+  int error;
+
+  // Read the raw values.
+  // Read 14 bytes at once,
+  // containing acceleration, temperature and gyro.
+  // With the default settings of the MPU-6050,
+  // there is no filter enabled, and the values
+  // are not very stable.
+  error = MPU6050_read (MPU6050_ACCEL_XOUT_H, (uint8_t *)accel_t_gyro, sizeof(accel_t_gyro_union));
+  if (error) return error;
+
+  // Swap all high and low bytes.
+  // After this, the registers values are swapped,
+  // so the structure name like x_accel_l does no
+  // longer contain the lower byte.
+  uint8_t swap;
+  #define SWAP(x,y) swap = x; x = y; y = swap
+
+  SWAP (accel_t_gyro->reg.x_accel_h, accel_t_gyro->reg.x_accel_l);
+  SWAP (accel_t_gyro->reg.y_accel_h, accel_t_gyro->reg.y_accel_l);
+  SWAP (accel_t_gyro->reg.z_accel_h, accel_t_gyro->reg.z_accel_l);
+  SWAP (accel_t_gyro->reg.t_h, accel_t_gyro->reg.t_l);
+  SWAP (accel_t_gyro->reg.x_gyro_h, accel_t_gyro->reg.x_gyro_l);
+  SWAP (accel_t_gyro->reg.y_gyro_h, accel_t_gyro->reg.y_gyro_l);
+  SWAP (accel_t_gyro->reg.z_gyro_h, accel_t_gyro->reg.z_gyro_l);
+}