How do I specify my register address for SPI driver interface?

[ndarkness]

Hello,

I am using SPI interface to communicate with a sensor BMI160, looking into the driver for BMI160 I can see how the low level functions for reading/writting are used like this

read(dev->id, reg_addr, data, len);

However, for nrf52 I see that spi transfer are defined as this

(nrf_drv_spi_transfer(&spi_BMI160, NULL, 0, rxData, bytesNumberRx)

where I have difined

static const nrf_drv_spi_t spi_BMI160 = NRF_DRV_SPI_INSTANCE(SPI_INSTANCE_1)

My question is pretty straightforward, how does know the SPI instance/driver what register reg_addr to write? Or where should I specifythat argurment ?

Thanks in advance,

[Jørgen Holmefjord]

Hi,

This should be documented in the datasheet of your device. Typically, the first byte transferred is the register address. You have not defined any TX buffer in the call to nrf_drv_spi_transfer, so you will not be able to write anything to the device.

Best regards,

Jørgen

[ndarkness]

Hi Jorgen thanks for replying, if the use the call like this. THen first I have to write which register I want to read? I think that it is that you address the register to read and perform a reading from it, am I wrong? Thus I would have to make a call to nrf_driver_spi_transfer specifying the register to be written, like this APP_ERROR_CHECK(nrf_drv_spi_transfer(&spi_BMI160, &reg_addr, 1, rxData, bytesNumberRx)); right?

[Jørgen Holmefjord]

Yes, something like that should work. Have you tested it?

[ndarkness]

My sensor hasn't arrived yet, so it is hard to test :S In case of the write function, I should set the read buffer as well?

[ndarkness]

So for writting something like this APP_ERROR_CHECK(nrf_drv_spi_transfer(&spi_BMI160, slaveDeviceId,sizeof(slaveDeviceId), NULL, 0)); Or I should do two writings? `