Hi Ceranthor,
1.hardware For BMI270 part, it is recommended to use 100 nf decoupling capacitors at pin 5(VDDIO) and pin 8(VDD). For BMM150 part, CSB and SDO pin should be connected to GND or VDDIO, refer BMM150 data sheet:
2. software You can refer github https://github.com/boschsensortec/BMI270-Sensor-API/blob/master/bmi270_examples/read_aux_data_mode/read_aux_data_mode.c example code
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