The SPI protocol for magnetic unit inside BMX055 is same as Accel and gyro part of BMX055.  So the code works for accel and gyro should also work for magnetic part. One thing need to care about, for magnetic part, CSB3 are also used for i2c address selection.  so if you use it under i2c mode before, this pin is pull down or pull high by external register or directly tie to VDDIO / GND.  For working under SPI mode, you should release the pin to make host controllable.  One more hint:  in your sample code, you read lsb and msb data from sensor in two SPI read action.  it is not recommend to do so.  In order to get correct data from sensor, you need to do burst read for both sensor from the register.  ... View more

These two API itself are only do some register read / write then trigger some action inside sensor.  So they should not use so much memory if the implemetation of API is correct.  Suggest you to check how you call the API in your code ... View more

Can you provide some detail information as following: 1. which ODR you are current using 2. which power mode you are current using (normal or low power mode) 3.  when you turn off the GPIO of host MCU for VDD and VDDIO of sensor, is the I2C bus still powered?  4.  when you mean turn on / off a set of sensors, do you mean BMI160 or other sensor on the same bus which cause BMI160 data spike?  ... View more

Why not directly use "Quaternion" from BNO055 for your calculation?  we are output querternion vector with "w,x,y,z" then you can use matlab to convert to your expected coordination directly ... View more

The overall procedue looks OK.  it should be as following: 1. Enable acceleration sensor (by default enabled after power up the sensor) 2. Set to 8G range 3. enable self test for x-axis with 21 4. wait 50 ms to read data 5. enable self test for x-axis with 17 6. wait 50 ms to read data Then calculate the difference between two read. Back to your case,  i have two comments: 1. please make sure the accel is in normal mode before self test (Accel 0x11 register with 0x00) 2. the read back value from 0x32 should be same as you write.  if you always read as 0 means sensor is in deep suspend mode ... View more