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 

[awneil]

arshdeep said:

Can you please direct me to the document

The Product Specification (aka "datasheet") is the document which describes the hardware capabilities & operation.

From there, you can either write your own driver, or use the driver provided in the SDK.

Write your own: www.8052mcu.com/.../160143

SDK documentation is here: http://infocenter.nordicsemi.com/topic/com.nordic.infocenter.sdk/dita/sdk/sdk.html?cp=4

Specifically for hardware drivers:  http://infocenter.nordicsemi.com/topic/com.nordic.infocenter.sdk5.v15.2.0/hardware_drivers.html?cp=4_0_0_2

[Einar Thorsrud]

Hi,

I recommend you use the SPI master driver, which will handle everything for you. The SPI hardware peripheral and SPI driver count 8 bit words but that does not have any practical implication for what happens on the SPI line. How you think of the data is up to you, whether you think of it as a single 16 bit word or two 8 bit words has no implication on the physical data on the SPI bus.

[arshdeep]

I realized that first i should understand the SPI examples provided in the SDK thoroughly before customizing them.

I am using nrf52832 DK as Master and flashing SPI example to it which is supposed to send a string " NORDIC " and then i am flashing SPIS example to my nrf52840 DK which should act as the slave then.  Now, though the transactions are getting completed in both the kits and LED's get toggled but i am not receiving the string "NORDIC" from my slave . What do i have to modify in the slave example to receive the string ?

#include "sdk_config.h"
#include "nrf_drv_spis.h"
#include "nrf_gpio.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 SPIS_INSTANCE 1 /**< SPIS instance index. */
static const nrf_drv_spis_t spis = NRF_DRV_SPIS_INSTANCE(SPIS_INSTANCE);/**< SPIS instance. */

#define TEST_STRING "Nordic"
static uint8_t       m_tx_buf[] = TEST_STRING;           /**< TX buffer. */
static uint8_t       m_rx_buf[sizeof(TEST_STRING) + 1];    /**< RX buffer. */
static const uint8_t m_length = sizeof(m_tx_buf);        /**< Transfer length. */

static volatile bool spis_xfer_done; /**< Flag used to indicate that SPIS instance completed the transfer. */

/**
 * @brief SPIS user event handler.
 *
 * @param event
 */
void spis_event_handler(nrf_drv_spis_event_t event)
{
    if (event.evt_type == NRF_DRV_SPIS_XFER_DONE)
    {
        spis_xfer_done = true;
        NRF_LOG_INFO(" Transfer completed. Received: %s",(uint32_t)m_rx_buf);
        printf("recieved : %s", m_rx_buf );
    }
}

int main(void)
{
    // Enable the constant latency sub power mode to minimize the time it takes
    // for the SPIS peripheral to become active after the CSN line is asserted
    // (when the CPU is in sleep mode).
    NRF_POWER->TASKS_CONSTLAT = 1;

    bsp_board_init(BSP_INIT_LEDS);

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

    NRF_LOG_INFO("SPIS example");

    nrf_drv_spis_config_t spis_config = NRF_DRV_SPIS_DEFAULT_CONFIG;
    spis_config.csn_pin               = APP_SPIS_CS_PIN;
    spis_config.miso_pin              = APP_SPIS_MISO_PIN;
    spis_config.mosi_pin              = APP_SPIS_MOSI_PIN;
    spis_config.sck_pin               = APP_SPIS_SCK_PIN;

    APP_ERROR_CHECK(nrf_drv_spis_init(&spis, &spis_config, spis_event_handler));

    while (1)
    {
        memset(m_rx_buf, 0, m_length);
        spis_xfer_done = false;

        APP_ERROR_CHECK(nrf_drv_spis_buffers_set(&spis, m_tx_buf, m_length, m_rx_buf, m_length));

        while (!spis_xfer_done)
        {
            __WFE();
        }

        NRF_LOG_FLUSH();

        bsp_board_led_invert(BSP_BOARD_LED_0);
    }
}

[arshdeep]

Also, in the code attached, if my m_length = 4. Will an SPI transaction end after every 8bit transfer and CS line will go high again or will the transaction end after all the 4 bytes are sent ???? 

 while (1)
    {
        // Reset rx buffer and transfer done flag
        memset(m_rx_buf, 0, m_length);
        spi_xfer_done = false;

        APP_ERROR_CHECK(nrf_drv_spi_transfer(&spi, &start_write, m_length, m_rx_buf, m_length));
        APP_ERROR_CHECK(nrf_drv_spi_transfer(&spi, &config_addr, m_length, m_rx_buf, m_length));
        APP_ERROR_CHECK(nrf_drv_spi_transfer(&spi, &config_lowvalue, m_length, m_rx_buf, m_length));
        APP_ERROR_CHECK(nrf_drv_spi_transfer(&spi, &config_highvalue, m_length, m_rx_buf, m_length));

        while (!spi_xfer_done)
        {
            __WFE();
        }

        NRF_LOG_FLUSH();

        bsp_board_led_invert(BSP_BOARD_LED_0);
        nrf_delay_ms(200)

[Einar Thorsrud]

Hi.

The SPI Master and SPI Slave example in the SDK can be used without any modification and demonstrates sending the string "Nordic" in both directions. The only thing you do is to flash both boards with the example and hook them up as specified in the SPI Slave Example documentation.

The length parameters defines the length of a transaction, yes. So if you set 4 for both Rx and Tx the transaction will be 4 bytes.