how to drive spi CS line low for 32 bits.

[arshdeep]

Hi,

Can you please direct me to the document that explains about generating more than 8 bits of clock in SPI and keeping CS line low for that entire period.

Also, if i have to send two 16bit data, would i have to send them in lots of 8bit ? or i can send them as 16bits using nrf_drv_spi_transfer API?

I am modifying the SPI example found under SDK15/example/peripheral/spi.

And i have to achieve the sequence attached in the image. 

Thank you 

[Håkon Alseth]

Hi,

 

You are not waiting for the SPI transfer to be finished (missing while(!spi_xfer_done)).

Since you initialize the SPI driver with a spi_handler set, this will set the driver into non-blocking mode. If you want blocking mode, set the handler to NULL when initializing the driver.

Kind regards,

Håkon

[arshdeep]

Hi Hakon,

I need to enable pull ups on SPI lines. Datasheet of IC recommends to use 10K pull up resistors on SPI lines . How can I enable internal pull ups on SPI lines ? I have used  nrf_gpio_cfg_output API to enable PULL UPS by changing its definition in nrf_gpio.h like this : 

__STATIC_INLINE void nrf_gpio_cfg_output(uint32_t pin_number)
{
    nrf_gpio_cfg(
        pin_number,
        NRF_GPIO_PIN_DIR_OUTPUT,
        NRF_GPIO_PIN_INPUT_DISCONNECT,
        NRF_GPIO_PIN_PULLUP,
        NRF_GPIO_PIN_S0S1,
        NRF_GPIO_PIN_NOSENSE);
}

Is this the right way to do so or there is any other better way also??

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 */
#include "nrf_drv_spi.h"
#include "app_util_platform.h"
#include "nrf_gpio.h"
#include "nrf_delay.h"
#include "boards.h"
#include "app_error.h"
#include <string.h>
#include "nrf_log.h"
#include "nrf_log_ctrl.h"
#include "nrf_log_default_backends.h"

#define SPI_INSTANCE  0 /**< SPI instance index. */
static const nrf_drv_spi_t spi = NRF_DRV_SPI_INSTANCE(SPI_INSTANCE);  /**< SPI instance. */
static volatile bool spi_xfer_done;  /**< Flag used to indicate that SPI instance completed the transfer. */


static uint32_t       m_tx_buf4= 0b10000000001100000000000000000000;    //0X80BC
//static uint16_t       m_tx_buf5= 0b;
 
 



static uint16_t       m_rx_buf1[2];    /**< RX buffer. */
static const uint8_t  m_length1 = 4;        /**< Transfer length. */

/**
 * @brief SPI user event handler.
 * @param event
 */



void spi_event_handler(nrf_drv_spi_evt_t const * p_event,
                       void *                    p_context)
{
    spi_xfer_done = true;
    NRF_LOG_INFO("Transfer completed.");
    if (m_rx_buf1[0] != 0)
    {
        NRF_LOG_INFO(" Received:");
        NRF_LOG_HEXDUMP_INFO(m_rx_buf1, strlen((const char *)m_rx_buf1));
    }
}

int main(void)
{
        bsp_board_init(BSP_INIT_LEDS);

        APP_ERROR_CHECK(NRF_LOG_INIT(NULL));
        NRF_LOG_DEFAULT_BACKENDS_INIT();



        nrf_drv_spi_config_t spi_config = NRF_DRV_SPI_DEFAULT_CONFIG;
        spi_config.ss_pin   = SPI_SS_PIN;
        spi_config.miso_pin = SPI_MISO_PIN;
        spi_config.mosi_pin = SPI_MOSI_PIN;
        spi_config.sck_pin  = SPI_SCK_PIN;
        spi_config.mode = NRF_DRV_SPI_MODE_2;

        nrf_gpio_cfg_output(SPI_SS_PIN);
        nrf_gpio_cfg_input(SPI_MISO_PIN, NRF_GPIO_PIN_PULLUP);
        nrf_gpio_cfg_output(SPI_MOSI_PIN);
        nrf_gpio_cfg_output(SPI_SCK_PIN);
        
        APP_ERROR_CHECK(nrf_drv_spi_init(&spi, &spi_config, spi_event_handler, NULL));

       NRF_LOG_INFO("SPI example started.");

        memset(m_rx_buf1, 0, m_length1);
        spi_xfer_done = false;

          //Send 80H to BCH to read power factor from BCH register
        APP_ERROR_CHECK(nrf_drv_spi_transfer(&spi, &m_tx_buf4, m_length1, m_rx_buf1, m_length1));
          
         while (!spi_xfer_done)
        {
            __WFE();
        }

        
      
        NRF_LOG_FLUSH();
        bsp_board_led_invert(3);
        nrf_delay_ms(200);


      
      //  memset(m_rx_buf1, 0, m_length1);
      //  spi_xfer_done = false;
       // APP_ERROR_CHECK(nrf_drv_spi_transfer(&spi, &m_tx_buf5, m_length1, m_rx_buf1, m_length1));
          
      //    while (!spi_xfer_done)
      //  {
      //      __WFE();
      //  }

      //  NRF_LOG_FLUSH();
      //  bsp_board_led_invert(2);
      //  nrf_delay_ms(200);

   }

Thanks,

[Håkon Alseth]

Hi,

 

I am sorry for the late reply.

You cannot enable pull up on a gpio configured as output. If you need a pull-resistor on a GPIO configured as output, you can either set the level (1 or 0), or add an external pull-resistor.

Kind regards,

Håkon

[arshdeep]

Hi Hakon,

I am still struggling to produce correct SPI timings . Below is the actual SPI timing sent to me by an Application Engineer from MICROCHIP. I need to replicate the same using nrf52840 chip :

I am getting these SPI timings using the same operation as in above image through nrf52840 chip . 

Can you identify what is going wrong with my attached firmware ????

Any kind of help or suggestion will be appreciated . We are really running late now on our project .

#include "nrf_drv_spi.h"
#include "app_util_platform.h"
#include "nrf_gpio.h"
#include "nrf_delay.h"
#include "boards.h"
#include "app_error.h"
#include <string.h>
#include "nrf_log.h"
#include "nrf_log_ctrl.h"
#include "nrf_log_default_backends.h"

#define SPI_INSTANCE  0 /**< SPI instance index. */
static const nrf_drv_spi_t spi = NRF_DRV_SPI_INSTANCE(SPI_INSTANCE);  /**< SPI instance. */
static volatile bool spi_xfer_done;  /**< Flag used to indicate that SPI instance completed the transfer. */


static uint16_t       m_tx_buf4= 0b1000000000110000;    //0X30H
static uint16_t       m_tx_buf5= 0b0000000000000000;
 

static uint8_t       m_rx_buf[2];    /**< RX buffer. */
static const uint8_t  m_length = 4;        /**< Transfer length. */

/**
 * @brief SPI user event handler.
 * @param event
 */



void spi_event_handler(nrf_drv_spi_evt_t const * p_event,
                       void *                    p_context)
{
    spi_xfer_done = true;
    NRF_LOG_INFO("Transfer completed.");
    if (m_rx_buf[0] != 0)
    {
        NRF_LOG_INFO(" Received:");
        NRF_LOG_HEXDUMP_INFO(m_rx_buf, strlen((const char *)m_rx_buf));
    }
}

int main(void)
{
    bsp_board_init(BSP_INIT_LEDS);

    APP_ERROR_CHECK(NRF_LOG_INIT(NULL));
    NRF_LOG_DEFAULT_BACKENDS_INIT();

        nrf_drv_spi_config_t spi_config = NRF_DRV_SPI_DEFAULT_CONFIG;
        spi_config.ss_pin   = SPI_SS_PIN;
        spi_config.miso_pin = SPI_MISO_PIN;
        spi_config.mosi_pin = SPI_MOSI_PIN;
        spi_config.sck_pin  = SPI_SCK_PIN;
        spi_config.mode = NRF_DRV_SPI_MODE_0;
        APP_ERROR_CHECK(nrf_drv_spi_init(&spi, &spi_config, spi_event_handler, NULL));

        NRF_LOG_INFO("SPI example started.");

        while(1){

        memset(m_rx_buf, 0, m_length);
        spi_xfer_done = false;
       
        APP_ERROR_CHECK(nrf_drv_spi_transfer(&spi, &m_tx_buf4, m_length, m_rx_buf, m_length));
        
              while (!spi_xfer_done)
        {
            __WFE();
        }

        NRF_LOG_FLUSH();


        bsp_board_led_invert(3);
        nrf_delay_ms(200);  

      }
    
}

Thanks,

Arshdeep

[Håkon Alseth]

Hi,

 

1. You are overflowing your buffer (m_rx_buffer) by 2 bytes, as the buffer is declared as 2 byte and you are receiving 4 bytes. This is _very crucial_ that you fix.

2. You are no longer switching SPI mode as per the spec for the sensor you are communicating with.

Best regards,

Håkon