BMI088 Accelerometer read "feature"

[dl1uj]

Hello,

I started to write a very small driver for the BMI088. While the gyroscope is working like expected, The accelerometer has a stange “feature”. Writing to it works fine, but reading any register gives the value of the previous read request. To read the xyz values I have to write twice to the register 0x12 to get the proper axis values like this:

ACC_ENABLE();

spi_transfer(ACC_X_LSB_12 | 0x80); // Start register read

spi_transfer(ACC_X_LSB_12 | 0x80); // Again start register read (why ever!)

ax = spi_transfer(0xFF);   ax += spi_transfer(0xFF) << 8;

ay = spi_transfer(0xFF);   ay += spi_transfer(0xFF) << 8;

az = spi_transfer(0xFF);   az += spi_transfer(0xFF) << 8;

ACC_DISABLE();

With this workaround the raw values for the IMU are fine. Does anyone know why the reading result is shifted by one operation? Looks like it´s caused by the FIFO, but I don´t write anything to it. Any help is welcome. Doing almost the same with the BMI055 worked without any problems.

Greetings from Germany

Udo

[Vincent · Accepted solution]

For BMI088 accel,  the default interface is configged as I2C,  you need a dummy read of SPI to switch to SPI bus first. 

Also you need a dummy byte during SPI read from the accel part.

You can refer to our BMI088 API on Github from following link:

https://github.com/BoschSensortec/BMI08x-Sensor-API

[gigamonte]

When selecting SPI for BMI088 accelerometer, does the datasheet indicate that the user has an option between toggling the PS pin and sending a dummy read or do both need to be done? It's not clear.

[Minhwan]

Hello gigamonte, 

SPI CS pin and dummy data for BMI088 are necessary. 

Thanks,