Cannot retrieve data from BMI270 using SPI on nRF52840

Question

Hi,

I have the following problem.

I have a custom board where I have BMI270 connected with SPI.

I use the nrfx_spim library.

I get error codes as a success when I try to write and read to SPI, however, I always get 0x00.

So I assume the problem has to be with the configuration of the hardware. The board is professionally made by a manufacturer, so the problem is not here, but rather in my configuration.

Here is my dts file part with the configuration for SPI, I tried using BMI270 predefined profile, and also manually, but none of them worked for me.

On my board connections are:

BMI270 SDO/MISO -> P0.20

BMI270 SDI/MOSI -> P0.22

BMI270 SCK -> P0.24

BMI270 CS -> P1.00

&gpio0 {
	status = "okay";
};

&gpio1 {
	status = "okay";
};

&spi1 {
	status = "okay";
	bmi270@0 {
		compatible = "bosch,bmi270";
		reg = <0>;
		spi-max-frequency = <DT_FREQ_M(10)>;
	};

	pinctrl-0 = <&spi1_default>;
	pinctrl-names = "default";
	cs-gpios = <&gpio1 0 (GPIO_ACTIVE_LOW)>; // P1.00 as CS, active low
};

&pinctrl {
	spi1_default: spi1_default {
		group1 {
			psels = <NRF_PSEL(SPIM_SCK, 0, 24)>,
		   <NRF_PSEL(SPIM_MOSI, 0, 22)>,
		   <NRF_PSEL(SPIM_MISO, 0, 20)>;
		};
	};
};

I also tried enabling and disabling those CONFIG flags

CONFIG_SPI=y
CONFIG_BMI270=y

and finally my main.c looks like this

#include <zephyr/kernel.h>
#include "SEGGER_RTT.h"
#include "SEGGER_RTT_printf.c"
#include "nrfx_spim.h"

// SPI instance index. You can have multiple instances for different peripherals.
#define SPI_INSTANCE_ID 0

#define SPI_CS_PIN 32

// Create an SPI configuration structure
nrfx_spim_config_t spi_config = NRFX_SPIM_DEFAULT_CONFIG(
    NRF_GPIO_PIN_MAP(0, 24),  // SCK pin
    NRF_GPIO_PIN_MAP(0, 22),  // MOSI pin
    NRF_GPIO_PIN_MAP(0, 20),  // MISO pin
    NRF_GPIO_PIN_MAP(1, 0)    // CS pin
);

nrfx_spim_t spi_instance = NRFX_SPIM_INSTANCE(SPI_INSTANCE_ID);

void spi_write(uint8_t *data, size_t length) {
    nrfx_spim_xfer_desc_t xfer_desc = NRFX_SPIM_XFER_TX(data, length);
    nrfx_spim_xfer(&spi_instance, &xfer_desc, 0);
}

void spi_read(uint8_t *command, size_t command_length, uint8_t *response, size_t response_length) {
    nrfx_spim_xfer_desc_t xfer_desc = NRFX_SPIM_XFER_TRX(command, command_length, response, response_length);
    nrfx_spim_xfer(&spi_instance, &xfer_desc, 0);
}

static uint8_t bmi270_read_register(uint8_t reg_addr) {
    // Assuming the sensor uses single-byte addresses
    uint8_t tx_buf[] = {0x80 | 0x00, 0x00}; // 0x80 for read, followed by dummy byte
    uint8_t rx_buf[2] = {0};

    // Prepare transfer
    nrfx_spim_xfer_desc_t xfer_desc_tx = NRFX_SPIM_XFER_TX(tx_buf, sizeof(tx_buf));
    nrfx_spim_xfer_desc_t xfer_desc_rx = NRFX_SPIM_XFER_RX(rx_buf, sizeof(rx_buf));

    // Transfer
    nrfx_err_t err_code = nrfx_spim_xfer(&spi_instance, &xfer_desc_tx, 0);

    if (err_code != NRFX_SUCCESS) 
    {
        // Initialization failed
        SEGGER_RTT_WriteString(0, "Sending failed!\n");
        return -1;
    }
    else
    {
        SEGGER_RTT_WriteString(0, "Sending has been done successfully!\n");

    }

    k_sleep(K_MSEC(2000));

    err_code = nrfx_spim_xfer(&spi_instance, &xfer_desc_rx, 0);


    if (err_code != NRFX_SUCCESS) 
    {
        // Initialization failed
        SEGGER_RTT_WriteString(0, "Reading failed!\n");
        return -1;
    }
    else
    {
        SEGGER_RTT_WriteString(0, "Reading has been done successfully!\n");

    }

    // The received data is in rx_buf[1]
    return rx_buf[1];
}

int main(void)
{
        nrfx_err_t err_code = nrfx_spim_init(&spi_instance, &spi_config, NULL, NULL);
        if (err_code != NRFX_SUCCESS) 
        {
            // Initialization failed
            SEGGER_RTT_WriteString(0, "SPI init failed!\n");
            return -1;
        }
        else
        {
            SEGGER_RTT_WriteString(0, "SPI init performed successfully!\n");

        }
        
        uint8_t data_buffer_from_SPI = bmi270_read_register(0x00);
        //for(int i = 0; i < sizeof(data_buffer_from_SPI); i++)
        //{
            SEGGER_RTT_printf(0, "BMI270 data0: 0x%02X\n", data_buffer_from_SPI);
        //}
        
}

Everything looks good when checking error codes.