nRF Connect SDK: SPI communication is not working on nRF52840 dev kit

[Kalyan Agepati]

Hi nRF support team,

By using the nRF Connect SDK, I am trying to implement an SPI communication with the display module from my nRF52840 dev kit and nRF52840 as a master.
I have tried below test code. But I m not receiving invalid data on MOSI pin and also not receiving a proper clock signal.

Can you please share the working sample code of SPI as a master of nRFconnect SDK?

This is my .overlay configuration:
&spi3 {
    status = "okay";
    cs-gpios = <&gpio0 12 0>;

    stxxxx@0 {
        compatible = "sitronix,stxxxx";
        label = "STxxxx";
        spi-max-frequency = <2000000>;
        reg = <0>;
        };
};

nRFsdk Pin configuration:
CS  <-> P0.12
CLK <-> P1.15
MISO <-> P1.14
MOSI <-> P1.13

Test Code:
struct device *spi_dev;
struct spi_cs_control spi_cs;
        
const struct spi_config spi_cfg = {
    .operation = SPI_OP_MODE_MASTER | SPI_WORD_SET(8) | SPI_TRANSFER_MSB |
             SPI_MODE_CPOL | SPI_MODE_CPHA,
    .frequency = 2000000,
    //.slave = 0,
};

static void spi_init(void)
{

    spi_cs.gpio_dev = device_get_binding("STxxxx");
           spi_cs.gpio_pin = DT_INST_SPI_DEV_CS_GPIOS_PIN(0);
    spi_cs.delay = 0;
        spi_cs.gpio_dt_flags = GPIO_ACTIVE_LOW;
       
    //spi_cfg.cs = &spi_cs;

        printk("SPI Initiating...");
    spi_dev = device_get_binding("STxxxx");
    if (spi_dev == NULL) {
        printk("\n******* Display device not found.  Aborting test. *******\n");
        return;
    }
}

void spi_send(struct device *spi_dev)
{
    int err;
    static uint8_t tx_buffer[1];
    static uint8_t rx_buffer[1];

    const struct spi_buf tx_buf = {
        .buf = tx_buffer,
        .len = sizeof(tx_buffer)
    };
    const struct spi_buf_set tx = {
        .buffers = &tx_buf,
        .count = 1
    };

    struct spi_buf rx_buf = {
        .buf = rx_buffer,
        .len = sizeof(rx_buffer),
    };
    const struct spi_buf_set rx = {
        .buffers = &rx_buf,
        .count = 1
    };
    err = spi_transceive(spi_dev, &spi_cfg, &tx, &rx);
    if (err) {
        printk("SPI write error: %d\n", err);
    } else {
        /* Connect MISO to MOSI for loopback */
        printk("MISO TX sent: %x\n", tx_buffer[0]);
        printk("MOSI RX recv: %x\n", rx_buffer[0]);
    }    
            
}

void main(void)
{  
        printk("\n**** main() start... ****\n");
        //Initlize the SPI module
        spi_init();
    
        while (1)
    {
              spi_send(spi_dev);
              k_sleep(K_SECONDS(2));
    }
}

Thanks in advance.
Regards,
Kalyan

[Edvin]

Hello,

Your screenshot says you are sampling at 500kHz, but your SPI is running at 2MHz. Can you please try to sample using a higher sample rate on the logic analyzer?

[Kalyan Agepati]

Hi Edvin,

Thanks for the suggestion. Now I am able to see the proper clock coming on SCK pin but not seeing valid data received on the MOSI pin.

For your information, I have tried to transmit one byte '?' (x3f) data and expected to receive MOSI data signal should be 00111111 but I have received 00101000 which is not correct. Can you please let me know if anything I have missed in the SPI configuration and test code?

Thanks in advance.

Regards,

Kalyan

[Edvin]

Are you sure you didn't change the SPI config?

What happens if you try the following main.c file:

/*
* Copyright (c) 2012-2014 Wind River Systems, Inc.
*
* SPDX-License-Identifier: Apache-2.0
*/

#include <zephyr.h>
#include <sys/printk.h>
#include <drivers/spi.h>
#include <drivers/gpio.h>

#define LED_PIN 16
#define SS_PIN 31

#define TEST_STRING "Southic"

static const struct spi_config spi_cfg = {
	.operation = SPI_OP_MODE_MASTER | SPI_WORD_SET(8) | SPI_TRANSFER_MSB |
		     SPI_MODE_CPOL | SPI_MODE_CPHA,
	.frequency = 4000000,
	.slave = 0,
};

struct device * spi_dev;

static void spi_init(void)
{
	const char* const spiName = "SPI_1";
	spi_dev = device_get_binding(spiName);

	if (spi_dev == NULL) {
		printk("Could not get %s device\n", spiName);
		return;
	}
}

void spi_test_send(void)
{
	int err;
	static u8_t tx_buffer[8] = TEST_STRING;
	static u8_t rx_buffer[8];

	tx_buffer[0] = 0x3f;
	
	for (int i=0; i<sizeof(tx_buffer);i++)
	{
		//tx_buffer[i] = 0x61 + i;
		rx_buffer[i] = 0x00;
	}

	const struct spi_buf tx_buf = {
		.buf = tx_buffer,
		.len = sizeof(tx_buffer)
	};
	const struct spi_buf_set tx = {
		.buffers = &tx_buf,
		.count = 1
	};

	struct spi_buf rx_buf = {
		.buf = rx_buffer,
		.len = sizeof(rx_buffer),
	};
	const struct spi_buf_set rx = {
		.buffers = &rx_buf,
		.count = 1
	};
	
	err = spi_transceive(spi_dev, &spi_cfg, &tx, &rx);
	
	if (err) {
		printk("SPI error: %d\n", err);
	} else {
		/* Connect MISO to MOSI for loopback */
		printk("TX sent: ");
		for (uint8_t i=0; i<6; i++)
		{
			printk("%x", tx_buffer[i]);
		}
		printk("\r\nRX recv: ");
		for (uint8_t i=0; i<6; i++)
		{
			printk("%c", rx_buffer[i]);
		}
		printk("\r\n");
		//tx_buffer[0]++;
	}	
}

void main(void)
{
	int ret;
	bool my_bool = false;

	struct device * dev = device_get_binding("GPIO_0");
	if (!dev) {
		printk("Device not found\n");
		return;
	}
	ret = gpio_pin_configure(dev, LED_PIN, GPIO_OUTPUT_ACTIVE);
	if (ret < 0)
	{
		printk("failed %d", ret);
	}
	ret = gpio_pin_configure(dev, SS_PIN, GPIO_OUTPUT_ACTIVE);
	if (ret <0)
	{
		printk("failed %d", ret);
	}
	printk("SPIM Example\n");
	
	spi_init();
	

	while (1) {
		gpio_pin_set(dev, LED_PIN, my_bool);
		
		my_bool = !my_bool;
		printk("my_bool %d\r\n", my_bool);
		gpio_pin_set(dev, SS_PIN, false);
		spi_test_send();
		gpio_pin_set(dev, SS_PIN, true);
		k_sleep(K_MSEC(1000));
	}
}

(you can remove the LED pin output if you like. I used this for testing, and it prints "?outhic".

Does it do that for you as well? You should see it in the logic analyzer. Try to enable the following settings:

But with your own channels for mosi, miso and clock. 

BR,

Edvin

[Kalyan Agepati]

Hi Edvin,

Thanks for the quick response and changes.

I have connected CS to GND and now I am receiving the valid data on MOSI.

Regards,

Kalyan