False SPI events (XFER_DONE) are created

Question

Hello,

4-byte long SPI messages, "1234", are sent to nRF 52DK. The code in DK is attached below. The XFER_DONE event is created before the message ends, which happens very often. I tried to change message frequency, clock frequency, and lots of things. Nothing is changed.

The below figure shows the sent SPI messages containing "1234". The toggled port is on Channel 5 when XFER_DONE is created. The corresponding received messages are shown between asterisk symbols on the figure.

I need more accurate messaging. Any suggestion?

#include "sdk_config.h"
#include "nrf_delay.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. */
static uint8_t       m_tx_buf[4];   /**< TX buffer. */
static uint8_t       m_rx_buf[5];    /**< 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. */
static uint8_t count = 0; 
void spis_event_handler(nrf_drv_spis_event_t event){
    static uint8_t count = 0; 
    if (event.evt_type == NRF_DRV_SPIS_XFER_DONE){
        spis_xfer_done = true;
        nrf_gpio_pin_toggle(3);
        NRF_LOG_INFO("%d XFER: *%s*",count++,(uint32_t)m_rx_buf);
    }
}
int main(void)
{
    NRF_POWER->TASKS_CONSTLAT = 1;
    bsp_board_init(BSP_INIT_LEDS);
    nrf_gpio_cfg_output(3);
    nrf_gpio_pin_write(3, 0);
    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               = 28; //APP_SPIS_CS_PIN;    //port 0.31
    spis_config.miso_pin              = 31; //APP_SPIS_MISO_PIN;  //port 0.30
    spis_config.mosi_pin              = 30; //APP_SPIS_MOSI_PIN;  //port 0.29
    spis_config.sck_pin               = 29; //APP_SPIS_SCK_PIN;   //port 0.26
    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);
    }
}