SPI event handler not beeing called

[Bastian]

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?

[KevinL]

Hi Bastian,

I can't really help you much with your issue as I think I'm having the same issue. Do you enter the infinite loop in while(!spi_xfer_done) when you call from the context of a button event handler?

I have been advised to used the SPIM peripheral (nrfx_spim). Although this has not solved the issue for me yet, it does seem to be the currently advised go-to SPI peripheral.

[MartinBL]

Hi,

You should check the return code of nrf_drv_spi_transfer(). If the function of some reason fails, it will return an error code without starting any SPI transfers. Hence you will never get a call back, and you will be stuck in the while loop. 

[Bastian]

Hi Martin,

I put an APP_ERROR_CHECK around nrf_drv_spi_transfer and it did not raise an issue. I stepped throught the function and it seems like it runs as it is supposed to do. Return value of nrf_drv_spi_transfer is SUCCESS.

[MartinBL]

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. 

[Bastian]

thats it, thank you