Why is not my Timer triggered when configured through PPI and SPI?

Question

Hello,

I am trying to use ArrayList for EasyDMA along with PPI but I am not sure whether or not I am configuring it properly to be used with the SPI interface.

So far I have set it up as below, in order to test the transfer I am connecting the MISO pin to ground(through a resistor) to fill the buffer with a null value. However,I never see an interruption from the configured TIMER happening, I mean, I don't see while running a call to timer_event_handler ( I have set a break point on that handler and it seems not to be called...)

Any suggestions of what might be cause not to see that interruption?

Thanks in advance,

#define SPI_INSTANCE  0 /**< SPI instance index. */
#define BUFF_LENGTH 4   /**< Transfer length. */
#define BUFF_RX_LENGTH 100

typedef struct ArrayList{
  uint8_t buffer[BUFF_LENGTH];
} ArrayList_type;


static const nrf_drv_spi_t spi = NRF_DRV_SPI_INSTANCE(SPI_INSTANCE);  /**< SPI instance. */
static uint8_t       m_tx_buf[BUFF_LENGTH];  /**< TX buffer. */
//static uint8_t       m_rx_buf[BUFF_LENGTH];   /**< RX buffer. */
ArrayList_type m_rx_buf[BUFF_RX_LENGTH];  /**< RX buffer. */

static volatile bool burst_completed = false;
static volatile bool spi_xfer_done = false;  /**< Flag used to indicate that SPI instance completed the transfer. */

// PPI resrources
nrf_ppi_channel_t ppi_channel_spi;
nrf_ppi_channel_t ppi_channel_timer;

// Timer for burst read
const nrf_drv_timer_t timer = NRF_DRV_TIMER_INSTANCE(0);

void imu_select()
{
    nrf_gpio_pin_clear(SPIM0_SS_PIN);
}

void imu_deselect()
{
    nrf_gpio_pin_set(SPIM0_SS_PIN);
}

void burst_transfer_disable()
{
    ret_code_t err_code;

    // Configure short between spi end event and spi start task
    nrf_spim_shorts_disable(spi.p_registers, NRF_SPIM_SHORT_END_START_MASK);

    err_code = nrf_drv_ppi_channel_disable(ppi_channel_spi);
    APP_ERROR_CHECK(err_code);
    err_code = nrf_drv_ppi_channel_disable(ppi_channel_timer);
    APP_ERROR_CHECK(err_code);
    
    nrf_drv_timer_disable(&timer);

    imu_deselect();

    burst_completed = true;
}

void timer_event_handler(nrf_timer_event_t event_type, void* p_context)
{
    switch (event_type)
    {
        case NRF_TIMER_EVENT_COMPARE0:
            burst_transfer_disable();
            break;

        default:
            //Do nothing.
            break;
    }
}

static void burst_setup()
{
    uint32_t spi_end_evt;
    uint32_t timer_count_task;
    uint32_t timer_cc_event;
    ret_code_t err_code;       

    //Configure timer
    nrf_drv_timer_config_t timer_cfg = NRF_DRV_TIMER_DEFAULT_CONFIG;
    timer_cfg.mode = NRF_TIMER_MODE_COUNTER;
    err_code = nrf_drv_timer_init(&timer, &timer_cfg, timer_event_handler);
    APP_ERROR_CHECK(err_code);

    // Compare event after 4 transmissions
    nrf_drv_timer_extended_compare(&timer, NRF_TIMER_CC_CHANNEL0, 1, NRF_TIMER_SHORT_COMPARE0_CLEAR_MASK, true);

    timer_count_task = nrf_drv_timer_task_address_get(&timer, NRF_TIMER_TASK_COUNT);
    timer_cc_event = nrf_drv_timer_event_address_get(&timer,  NRF_TIMER_EVENT_COMPARE0);
    NRF_LOG_INFO("timer configured\n");

    // allocate PPI channels for hardware
    err_code = nrf_drv_ppi_channel_alloc(&ppi_channel_spi);
    APP_ERROR_CHECK(err_code);
    err_code = nrf_drv_ppi_channel_alloc(&ppi_channel_timer);
    APP_ERROR_CHECK(err_code);
    NRF_LOG_INFO("ppi allocated\n");

    spi_end_evt = nrf_drv_spi_end_event_get(&spi);

    // Configure the PPI to count the trasnsactions on the TIMER
    err_code = nrf_drv_ppi_channel_assign(ppi_channel_spi, spi_end_evt, timer_count_task);
    APP_ERROR_CHECK(err_code);


    // Configure another PPI to stop the SPI when 4 transactions have been completed
    err_code = nrf_drv_ppi_channel_assign(ppi_channel_timer, timer_cc_event, NRF_SPIM_TASK_STOP);
    APP_ERROR_CHECK(err_code);
    NRF_LOG_INFO("ppi configured\n");
}

static void burst_transfer_enable()
{
    ret_code_t err_code;

    burst_completed = false;

    err_code = nrf_drv_ppi_channel_enable(ppi_channel_spi);
    APP_ERROR_CHECK(err_code);
    err_code = nrf_drv_ppi_channel_enable(ppi_channel_timer);
    APP_ERROR_CHECK(err_code);

    nrf_drv_timer_enable(&timer);

    // Configure short between spi end event and spi start task
    nrf_spim_shorts_enable(spi.p_registers, NRF_SPIM_SHORT_END_START_MASK);

    imu_select();
}


void spi_event_handler(nrf_drv_spi_evt_t const * p_event)
{
    if(p_event->type == NRF_DRV_SPI_EVENT_DONE)
    {
    	spi_xfer_done = true;
    }
    else
    {
        NRF_LOG_ERROR("Wrong Event\n");
        // Something is wrong
    }
}

int8_t bmi160_bus_burst_read(uint8_t dev_addr, uint8_t reg_addr, uint8_t *reg_data, uint32_t cnt)
{
//    m_tx_buf[0] = reg_addr | READ_MASK;

    nrf_drv_spi_xfer_desc_t xfer = NRF_DRV_SPI_XFER_RX(m_rx_buf, 1);
    uint32_t flags = NRF_DRV_SPI_FLAG_HOLD_XFER |
                     NRF_DRV_SPI_FLAG_REPEATED_XFER |
                     NRF_DRV_SPI_FLAG_RX_POSTINC  |
                     NRF_DRV_SPI_FLAG_NO_XFER_EVT_HANDLER;
    nrf_drv_spi_xfer(&spi, &xfer, flags);  

    burst_transfer_enable();

    nrf_spim_task_trigger(spi.p_registers, NRF_SPIM_TASK_START);

    while(!burst_completed){
        NRF_LOG_INFO("wating for interruption\n");
//        __WFE();
    }
    spi_xfer_done = false;
    burst_completed = false;

    return NRF_SUCCESS;
}

int8_t spi_init(void)
{
    ret_code_t err_code;
    
    nrf_gpio_cfg_output(SPIM0_SS_PIN);
    imu_deselect();
    
    err_code = nrf_drv_ppi_init();
    APP_ERROR_CHECK(err_code);
    NRF_LOG_INFO("ppi initialised\n");
    
    nrf_drv_spi_config_t spi_config = NRF_DRV_SPI_DEFAULT_CONFIG;
    spi_config.ss_pin   = NRF_DRV_SPI_PIN_NOT_USED;		//I control the CS pin 
    spi_config.miso_pin = SPIM0_MISO_PIN;
    spi_config.mosi_pin = SPIM0_MOSI_PIN;
    spi_config.sck_pin  = SPIM0_SCK_PIN;                               
    APP_ERROR_CHECK(nrf_drv_spi_init(&spi, &spi_config, spi_event_handler));
    NRF_LOG_INFO("SPI1 Master initialised.\r\n");


    NRF_SPIM0->RXD.PTR  =  m_rx_buf;
    NRF_SPIM0->RXD.MAXCNT = BUFF_LENGTH;

    // Reset rx buffer and transfer done flag
    memset(m_rx_buf, 0x05, sizeof(ArrayList_type)*BUFF_RX_LENGTH);
    spi_xfer_done = false; 

//    // To read the Device ID (0xD1)
//    uint8_t data = 0;
//    bmi160_bus_read(0, 0x0, &data, 1);
//    NRF_LOG_INFO("DEVICE ID (0xD1): %#01x\r\n", data);

    return NRF_SUCCESS;
}

/**
 * @brief Function for application main entry.
 */
int main(void)
{
    burst_setup();
    spi_init();

    while (true)
    {
          bmi160_bus_burst_read(NULL,NULL,NULL,NULL);
    }
//    bmi160_bus_burst_read(NULL,NULL,NULL,NULL);
}