SPI event handler not beeing called

Question

Hi I am currently runnign into a problem that my SPI driver does not fire a spi_event after a while. 
 The code is as follows: 
 static volatile bool spi_xfer_done;

void spi_event_handler(nrf_drv_spi_evt_t const *p_event,
 void *p_context)
{
 spi_xfer_done = true;
}

void spi_data_write(unsigned char data)
{
 uint8_t rx;
 spi_xfer_done = false;
 nrf_gpio_pin_set(DISPLAY_DC); // DC = 1 for data packet
 nrf_drv_spi_transfer(&spi, &data, 1, &rx, 0);

 // hang in there
 while (!spi_xfer_done)
 {
 __WFE();
 }
 return;
}

void spi_init()
{
 // init SPI
 nrf_drv_spi_config_t spi_config = NRF_DRV_SPI_DEFAULT_CONFIG;
 spi_config.ss_pin = DISPLAY_CS; // NRF_DRV_SPI_PIN_NOT_USED;
 spi_config.mosi_pin = DISPLAY_SDI;
 spi_config.miso_pin = NRF_DRV_SPI_PIN_NOT_USED;
 spi_config.sck_pin = DISPLAY_SCLK;
 spi_config.frequency = NRF_DRV_SPI_FREQ_1M;
 spi_config.mode = NRF_DRV_SPI_MODE_0;
 spi_config.bit_order = NRF_DRV_SPI_BIT_ORDER_MSB_FIRST;
 nrf_drv_spi_init(&spi, &spi_config, spi_event_handler, NULL);
}
 
 The thing is, it is working at first. My main function is as follows: 
 static void bsp_event_handler(bsp_event_t event)
{
 switch (event)
 {
 case BSP_EVENT_KEY_3: // Button 4 pushed.
 NRF_LOG_INFO("Button 4 pressed");
 buttons |= 0x8;
 display_clear(&dsp, COLOR_WHITE);
 display_rect_fill(&dsp, 70, 70, 10, 10, COLOR_BLACK);
 display_render(&dsp);
 break;

 default:
 NRF_LOG_INFO("Button pressed");
 break;
 }
}


int main(void)
{
 char loop;
 // initialize logger
 APP_ERROR_CHECK(NRF_LOG_INIT(NULL));
 NRF_LOG_DEFAULT_BACKENDS_INIT();

 lfclk_config();
 NRF_LOG_INFO("LFClock init done");
 NRF_LOG_FLUSH();
 APP_ERROR_CHECK(app_timer_init());
 timer_interrupt_init();

 nrf_pwr_mgmt_init();

 APP_ERROR_CHECK(bsp_init(BSP_INIT_BUTTONS, bsp_event_handler));

 // initalize the display
 NRF_LOG_INFO("initialize display");
 display_init(&dsp);
 // draw splash screen
 NRF_LOG_INFO("draw splash");
 sw_splashscreen(&dsp);
 display_render(&dsp);
 APP_ERROR_CHECK(app_timer_start(m_timer, APP_TIMER_TICKS(5000), NULL));

 while (true)
 {
 NRF_LOG_INFO("loop: %d", loop++);
 NRF_LOG_FLUSH();
 app_sched_execute();
 nrf_pwr_mgmt_run();
 }
} 
 It works at first, the diosplay is switched on and displays the slapsh image as intendet in main. But everything after that using the SPI transfer function casues to infinite loop in 
 
 while ( ! spi_xfer_done) 
 
 what might cause this behaviour?

MartinBL · Accepted Answer

It could be an issue with interrupt nesting. It seems like you start the SPI transfer from within the BSP event handler. If the SPI has lower interrupt priority than the BSP handler, then the SPI handler will not be executed before the BSP handler has completed. But since you are effectively waiting for the SPI in the BSP handler you end up in a dead lock.

SPI event handler not beeing called

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