Issue with reading WHO AM I Register of ICM20948 over SPI with nRF52832 and Zephyr

[vimok]

I am trying to read the WHO AM I register of an ICM20948 over SPI with nRF52832, but I am getting incorrect values.

I have tried different SPI modes, but none of them work. Later, I tried reading the same register to make sure the module is working with different controllers, and they worked, which means the module is functioning properly.

Instead of expected value 0xEA, I am getting 0xE0 or some other values.

// boards/nrf52dk_nrf52832.overlay

&i2c0 {	status = "disabled";};
&i2c1 {	status = "disabled";};
&spi1 {	status = "disabled";};

my_spi_master: &spi2 {
	compatible = "nordic,nrf-spi";
	status = "okay";
	pinctrl-0 = <&spi_master_default>;
	pinctrl-1 = <&spi_master_sleep>;
	pinctrl-names = "default", "sleep";
	cs-gpios = <&gpio0 28 GPIO_ACTIVE_LOW>;
	reg_my_spi_master: spi-dev-a@0 {
		reg = <0>;
	};
};

&pinctrl {
	spi_master_default: spi_master_default {
		group1 {
			psels = <NRF_PSEL(SPIM_SCK, 0, 25)>,
					<NRF_PSEL(SPIM_MOSI, 0, 23)>,
					<NRF_PSEL(SPIM_MISO, 0, 24)>;
		};
	};

	spi_master_sleep: spi_master_sleep {
		group1 {
			psels = <NRF_PSEL(SPIM_SCK, 0, 25)>,
					<NRF_PSEL(SPIM_MOSI, 0, 23)>,
					<NRF_PSEL(SPIM_MISO, 0, 24)>;
			low-power-enable;
		};
	};
};

#define MY_SPI_MASTER DT_NODELABEL(my_spi_master)
#define MY_SPI_MASTER_CS_DT_SPEC SPI_CS_GPIOS_DT_SPEC_GET(DT_NODELABEL(reg_my_spi_master))
const struct device *spi_dev;

static struct spi_config spi_cfg = {
    // .operation = SPI_TRANSFER_MSB | SPI_WORD_SET(8), // spi mode 0
    // .operation = SPI_TRANSFER_MSB | SPI_WORD_SET(8) | SPI_MODE_CPHA, // spi mode 1
    // .operation = SPI_TRANSFER_MSB | SPI_WORD_SET(8) | SPI_MODE_CPOL, // spi mode 2
    .operation = SPI_TRANSFER_MSB | SPI_WORD_SET(8) | SPI_MODE_CPOL | SPI_MODE_CPHA, // spi mode 3
    .frequency = 4000000,
    .slave = 0,
    .cs = {.gpio = MY_SPI_MASTER_CS_DT_SPEC, .delay = 0},
};

void read_register(uint8_t reg, uint8_t *data, uint32_t size)
{
    uint8_t tx_buffer[1];
    uint8_t rx_buffer[size];
    struct spi_buf tx_buf, rx_buf;

    tx_buffer[0] = reg;

    tx_buf.buf = tx_buffer;
    tx_buf.len = 1;
    rx_buf.buf = rx_buffer;
    rx_buf.len = size;

    struct spi_buf_set tx = { .buffers = &tx_buf, .count = 1 };
    struct spi_buf_set rx = { .buffers = &rx_buf, .count = 1 };

    int ret = spi_transceive(spi_dev, &spi_cfg, &tx, &rx);
    if (ret) {
        printk("SPI read failed with error code %d\n", ret);
        return;
    }

    memcpy(data, rx_buffer, size);
}

void spi_init(void)
{
    spi_dev = DEVICE_DT_GET(MY_SPI_MASTER);

    if (!device_is_ready(spi_dev))
    {
        printk("SPI master device not ready!\n");
    }

    struct gpio_dt_spec spim_cs_gpio = MY_SPI_MASTER_CS_DT_SPEC;

    if (!device_is_ready(spim_cs_gpio.port))
    {
        printk("SPI master chip select device not ready!\n");
    }
}

int main(void)
{
    int err;

    spi_init();

    uint8_t reg;
    uint8_t data[2] = {0};

    reg = 0x00 | 0x80;

    read_register(reg, data, 2);
}

Also I am getting the following problem in overlay file but I am able to compile and run the code. I restarted the VS Code but the problem persists.

nRF Connect SDK v2.6.1. 

[Håkon Alseth]

Hi,

 

Have you scoped the SPI signals to see how the pins behave, and if they behave as expected?

If yes, can you share the result here?

 

Kind regards,

Håkon

[vimok]

I removed the sensor and connected the pins on logic analyser and am finding issues.

1. There is no clock signal

2. CS pin is getting high too soon

Will try to probe more and see what is going on.

[Håkon Alseth]

Hi,

 

Don't take away the sensor. Scope the pins with the sensor connected, and trace from reboot.

PS: What is your sampling rate in your logic analyzer? It looks to be 800 Hz, which is way to low of a sampling rate. You should have atleast 8 MHz (preferably 4*Fs, ie. 16 MHz)

Kind regards,

Håkon

[vimok]

I made the following change and the code is working now.

Thank you for the suggestions.

void read_register(uint8_t reg, uint8_t *data, uint32_t size)
{
    int ret;

    struct spi_buf tx_buf = {
        .buf = &reg,
        .len = 1,
    };

    struct spi_buf rx_buf[] = {
        {.buf = NULL, .len = 1},
        {.buf = data, .len = size},
    };

    struct spi_buf_set tx = {.buffers = &tx_buf, .count = 1};
    struct spi_buf_set rx = {.buffers = &rx_buf, .count = ARRAY_SIZE(rx_buf)};

    ret = spi_transceive(spi_dev, &spi_cfg, &tx, &rx);
    if (ret) {
        printk("SPI read failed with error code %d\n", ret);
        return;
    }
}

[Håkon Alseth]

Hi,

 

I'm glad to hear that you got the communication up and running!

 

Kind regards,

Håkon