text: # mpu9250.py MicroPython driver for the InvenSense MPU9250 inertial measurement unit
  # Authors Peter Hinch, Sebastian Plamauer
  # V0.5 17th June 2015
  
  '''
  mpu9250 is a micropython module for the InvenSense MPU9250 sensor.
  It measures acceleration, turn rate and the magnetic field in three axis.
  
  The MIT License (MIT)
  Copyright (c) 2014 Sebastian Plamauer, oeplse@gmail.com, Peter Hinch
  Permission is hereby granted, free of charge, to any person obtaining a copy
  of this software and associated documentation files (the "Software"), to deal
  in the Software without restriction, including without limitation the rights
  to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
  copies of the Software, and to permit persons to whom the Software is
  furnished to do so, subject to the following conditions:
  The above copyright notice and this permission notice shall be included in
  all copies or substantial portions of the Software.
  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
  AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
  OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
  THE SOFTWARE.
  '''
  
  from imu import MPU6050, bytes_toint, MPUException
  from vector3d import Vector3d
  
  
  class MPU9250(MPU6050):
      '''
      MPU9250 constructor arguments
      1. side_str 'X' or 'Y' depending on the Pyboard I2C interface being used
      2. optional device_addr 0, 1 depending on the voltage applied to pin AD0 (Drotek default is 1)
         if None driver will scan for a device (if one device only is on bus)
      3, 4. transposition, scaling optional 3-tuples allowing for outputs to be based on vehicle
            coordinates rather than those of the sensor itself. See readme.
      '''
  
      _mag_addr = 12          # Magnetometer address
      _chip_id = 113
  
      def __init__(self, side_str, device_addr=None, transposition=(0, 1, 2), scaling=(1, 1, 1)):
  
          super().__init__(side_str, device_addr, transposition, scaling)
          self._mag = Vector3d(transposition, scaling, self._mag_callback)
          self.accel_filter_range = 0             # fast filtered response
          self.gyro_filter_range = 0
          self._mag_stale_count = 0               # MPU9250 count of consecutive reads where old data was returned
          self.mag_correction = self._magsetup()  # 16 bit, 100Hz update.Return correction factors.
          self._mag_callback()  # Seems neccessary to kick the mag off else 1st reading is zero (?)
  
      @property
      def sensors(self):
          '''
          returns sensor objects accel, gyro and mag
          '''
          return self._accel, self._gyro, self._mag
  
      # get temperature
      @property
      def temperature(self):
          '''
          Returns the temperature in degree C.
          '''
          try:
              self._read(self.buf2, 0x41, self.mpu_addr)
          except OSError:
              raise MPUException(self._I2Cerror)
          return bytes_toint(self.buf2[0], self.buf2[1])/333.87 + 21  # I think
  
      # Low pass filters
      @property
      def gyro_filter_range(self):
          '''
          Returns the gyro and temperature sensor low pass filter cutoff frequency
          Pass:               0   1   2   3   4   5   6   7
          Cutoff (Hz):        250 184 92  41  20  10  5   3600
          Sample rate (KHz):  8   1   1   1   1   1   1   8
          '''
          try:
              self._read(self.buf1, 0x1A, self.mpu_addr)
              res = self.buf1[0] & 7
          except OSError:
              raise MPUException(self._I2Cerror)
          return res
  
      @gyro_filter_range.setter
      def gyro_filter_range(self, filt):
          '''
          Sets the gyro and temperature sensor low pass filter cutoff frequency
          Pass:               0   1   2   3   4   5   6   7
          Cutoff (Hz):        250 184 92  41  20  10  5   3600
          Sample rate (KHz):  8   1   1   1   1   1   1   8
          '''
          if filt in range(8):
              try:
                  self._write(filt, 0x1A, self.mpu_addr)
              except OSError:
                  raise MPUException(self._I2Cerror)
          else:
              raise ValueError('Filter coefficient must be between 0 and 7')
  
      @property
      def accel_filter_range(self):
          '''
          Returns the accel low pass filter cutoff frequency
          Pass:               0   1   2   3   4   5   6   7 BEWARE 7 doesn't work on device I tried.
          Cutoff (Hz):        460 184 92  41  20  10  5   460
          Sample rate (KHz):  1   1   1   1   1   1   1   1
          '''
          try:
              self._read(self.buf1, 0x1D, self.mpu_addr)
              res = self.buf1[0] & 7
          except OSError:
              raise MPUException(self._I2Cerror)
          return res
  
      @accel_filter_range.setter
      def accel_filter_range(self, filt):
          '''
          Sets the accel low pass filter cutoff frequency
          Pass:               0   1   2   3   4   5   6   7 BEWARE 7 doesn't work on device I tried.
          Cutoff (Hz):        460 184 92  41  20  10  5   460
          Sample rate (KHz):  1   1   1   1   1   1   1   1
          '''
          if filt in range(8):
              try:
                  self._write(filt, 0x1D, self.mpu_addr)
              except OSError:
                  raise MPUException(self._I2Cerror)
          else:
              raise ValueError('Filter coefficient must be between 0 and 7')
  
      def _magsetup(self):                        # mode 2 100Hz continuous reads, 16 bit
          '''
          Magnetometer initialisation: use 16 bit continuous mode.
          Mode 1 is 8Hz mode 2 is 100Hz repetition
          returns correction values
          '''
          try:
              self._write(0x0F, 0x0A, self._mag_addr)      # fuse ROM access mode
              self._read(self.buf3, 0x10, self._mag_addr)  # Correction values
              self._write(0, 0x0A, self._mag_addr)         # Power down mode (AK8963 manual 6.4.6)
              self._write(0x16, 0x0A, self._mag_addr)      # 16 bit (0.15uT/LSB not 0.015), mode 2
          except OSError:
              raise MPUException(self._I2Cerror)
          mag_x = (0.5*(self.buf3[0] - 128))/128 + 1
          mag_y = (0.5*(self.buf3[1] - 128))/128 + 1
          mag_z = (0.5*(self.buf3[2] - 128))/128 + 1
          return (mag_x, mag_y, mag_z)
  
      @property
      def mag(self):
          '''
          Magnetomerte object
          '''
          return self._mag
  
      def _mag_callback(self):
          '''
          Update magnetometer Vector3d object (if data available)
          '''
          try:                                    # If read fails, returns last valid data and
              self._read(self.buf1, 0x02, self._mag_addr)  # increments mag_stale_count
              if self.buf1[0] & 1 == 0:
                  return self._mag                # Data not ready: return last value
              self._read(self.buf6, 0x03, self._mag_addr)
              self._read(self.buf1, 0x09, self._mag_addr)
          except OSError:
              raise MPUException(self._I2Cerror)
          if self.buf1[0] & 0x08 > 0:             # An overflow has occurred
              self._mag_stale_count += 1          # Error conditions retain last good value
              return                              # user should check for ever increasing stale_counts
          self._mag._ivector[1] = bytes_toint(self.buf6[1], self.buf6[0])  # Note axis twiddling and little endian
          self._mag._ivector[0] = bytes_toint(self.buf6[3], self.buf6[2])
          self._mag._ivector[2] = -bytes_toint(self.buf6[5], self.buf6[4])
          scale = 0.15                            # scale is 0.15uT/LSB
          self._mag._vector[0] = self._mag._ivector[0]*self.mag_correction[0]*scale
          self._mag._vector[1] = self._mag._ivector[1]*self.mag_correction[1]*scale
          self._mag._vector[2] = self._mag._ivector[2]*self.mag_correction[2]*scale
          self._mag_stale_count = 0
  
      @property
      def mag_stale_count(self):
          '''
          Number of consecutive times where old data was returned
          '''
          return self._mag_stale_count
  
      def get_mag_irq(self):
          '''
          Uncorrected values because floating point uses heap
          '''
          self._read(self.buf1, 0x02, self._mag_addr)
          if self.buf1[0] == 1:                   # Data is ready
              self._read(self.buf6, 0x03, self._mag_addr)
              self._read(self.buf1, 0x09, self._mag_addr)    # Mandatory status2 read
              self._mag._ivector[1] = 0
              if self.buf1[0] & 0x08 == 0:        # No overflow has occurred
                  self._mag._ivector[1] = bytes_toint(self.buf6[1], self.buf6[0])
                  self._mag._ivector[0] = bytes_toint(self.buf6[3], self.buf6[2])
                  self._mag._ivector[2] = -bytes_toint(self.buf6[5], self.buf6[4])
  