Hi Larry,
If you don't use BMI270 sensor API, you need to perform the read ID action in the red box below to activate the SPI before you do reset or read chip ID.
The normal SPI waveform of reading chip ID and reset are like this:
If you use BMI270 sensor API, I uploaed example code on STM32 for your reference. Hope it is useful for you.
To use SPI, change the code in int8_t Init_BMI270(struct bmi2_dev *dev).
from rslt = bmi2_interface_init(dev, BMI2_I2C_INTF);
to rslt = bmi2_interface_init(dev, BMI2_SPI_INTF);
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