The cs pin of the spi is not working

[emmovo]

I'm having problems with the spi api for zephyr, maybe my spi peripherals are not configured correctly, I can see normal signal outputs from the clock and mosi signal lines, but the cs line stays pulled up and doesn't use any other outputs;

I am using the nrf52840dk and trying to drive the st7789v display via spi;

The sdk version I'm using is 2.5.0; the dts used is nrf52840dk_nrf52840;.

Here is the contents of my .overlay file:

&spi1 {
	status = "disabled";
};

&spi3 {
	status = "disabled";
};

&i2c0 {
	status = "disabled";
};

&qspi {
	status = "disabled";
};

&adc {
	status = "disabled";
};

&spi0 {
	status = "okay";
	cs-gpios = <&gpio0 30 GPIO_ACTIVE_LOW>;
};

&spi0_default {
	group1 {
		psels = <NRF_PSEL(SPIM_SCK, 0, 3)>, <NRF_PSEL(SPIM_MOSI, 0, 4)>;
	};
};

Here are the contents of my prj.conf:

CONFIG_NRFX_SPIM3=y 
CONFIG_SPI=y

My spi does it like this:

const struct device *spi= DEVICE_DT_GET(DT_NODELABEL(spi0));

struct spi_config spi_cfg = {
    .operation = SPI_OP_MODE_MASTER | SPI_TRANSFER_MSB | SPI_WORD_SET(8) | SPI_LINES_SINGLE ,
    .frequency = 8000000,
    .slave = 1,
    .cs = {
        .gpio = SPI_CS_GPIOS_DT_SPEC_GET(spi),
        .delay = 2,
    }
};

int SPI_init(void)
{
    if(!device_is_ready(spi))
    {
        printk("SPI device is not ready\n");
        return -1;
    }

    printk("is gpio %s\r\n", spi_cs_is_gpio(&spi_cfg.cs) ? "GPIO" : "Hardware CS");


    return 0;

}

void SPI_write(uint8_t *data, uint16_t len)
{
    struct spi_buf tx_buf = {
        .buf = data,
        .len = len
    };

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

    int ret = spi_write(spi, &spi_cfg, &tx);
}

Here is the git link to my code:

github.com/.../lcd_zephyr_spi

Any help I can get would be appreciated and very much appreciated!

[Vidar Berg]

Hello,

If you search for 'st7789v' in the SDK, you should find multiple references to how the device can be defined in the devicetree. There's also the Generic ST7789V Display Shield you can use. 

Best regards,

Vidar

[emmovo]

Thank you very much for your reminder, I already know that I can directly add the st7789v node through the device tree in order to achieve the driver display, and successfully complete the display function; however, I still want to know the reason why I used the spi way cs signal line above did not work properly; I worry that if I face other zephyr device tree later when there is no preset device, I don't know how to deal with it; I hope to get your support. I hope I can get your support, thanks!

[Vidar Berg]

I believe the problem in your case is that you have not specified any devices on your SPI bus, so the CS pin is not assigned to any device. 

Here is an example which use the SPI API directly:

https://github.com/too1/ncs-spi-master-slave-example/tree/master 

Notice that it defines a bus device in the overlay here: https://github.com/too1/ncs-spi-master-slave-example/blob/629db4cf8000605ddf46a5ac18936552bae3f52f/boards/nrf52840dk_nrf52840.overlay#L46 

[emmovo]

Thanks for the reminder, what you mean is that I need to mount a specific device under the spi node of the device tree for the cs to be assigned and thus have the appropriate slice selection action; if I simply configure the spi without a specific device, the cs won't have an action; am I understanding this correctly?

[Vidar Berg]

Yes, correct. That is what I would expect, at least. I've never tried to use the SPI node without specifying a bus device in the DT.

[emmovo]

My problem has been solved. As you said, after I mounted the spi with a special device in the device tree, the cs works fine. Thank you for your patient, professional and efficient technical support!