RNG interrupt handler not called

[David Anthony]

RNG interrupt handler is not called.

Using nrfx_rng library to generate random numbers.

VALRDY event is generated but interrupt handler nrfx_rng_irq_handler in library is not called.

Breakpoint not hit.

Despite EVENTS_VALRDY being set.

and INTENSET/ NVIC_ISER0 having correct values.

Code which sets up RNG using nrfx_rng library

ren_status_t generateRand(uint8_t * p_challenge)
{
ren_status_t return_value = RAND_ERROR;

static const nrfx_rng_config_t RNG_CONFIG = {
.error_correction = true,
.interrupt_priority = RNG_INTERRUPT_PRIORITY
};

assert(p_challenge != NULL);

challenge_pointer = p_challenge;

/* Reset random number counter. */
random_number_index = 0U;

/* Initialise random number generator. */
if (NRF_SUCCESS == nrfx_rng_init(&RNG_CONFIG, randomNumberEventHandler))
{
/* Start random number generator. */
nrfx_rng_start();

/* Wait for required number of random numbers to be generated. */
while(random_number_index < RAND_SIZE);

/* Stop random number generator. */
nrfx_rng_stop();

/* Uninitialise random number generator. */
nrfx_rng_uninit();

return_value = RAND_SUCCESS;
}

return return_value;
}



static void randomNumberEventHandler(uint8_t rng_data)
{
assert(challenge_pointer != NULL);

/* Store random number in appropriate location in challenge. */
rand_pointer[random_number_index] = rng_data;

/* Move on to next location. */
random_number_index++;
}

Any ideas ?

[akofoed]

Hi,

I seem to have a similar issue with the RNG. I am not using the SoftDevice but it seems that the RNG does not run the interrupt function no matter what priotity I give it.

The issue is when waiting for the RNG to generate the correct number of numbers.

Using while(random_number_index < len) {}; does not work, while nrf_delay_ms(1); does!

NRFX:

static int random_number_index;
static uint8_t *random_number_buf_ptr;
static int random_number_max_len;

void rng_event_handler(uint8_t rng_data)
{
    if (random_number_index < random_number_max_len)
    {
        random_number_buf_ptr[random_number_index] = rng_data;
        random_number_index++;
    }
}

int mcu_rng_generate(int len, uint8_t *rng_buf)
{
    // Reset random number counter
    random_number_index = 0;

    // Setup safety so that RNG does not fill up buffer beyound len
    random_number_max_len = len;
    random_number_buf_ptr = rng_buf;

    // Start random number generator
    nrfx_rng_start();

    // Wait for required number of random numbers to be generated
    // nrf_delay_ms(1); // <-- THIS WORKS
    while(random_number_index < len) {}; // <-- THIS DOES NOT WORK
    // NRF_LOG_INFO("%d < %d", random_number_index, len);

    // Stop random number generator
    nrfx_rng_stop();

    return NRF_SUCCESS;
}

// Random number generator
int mcu_rng_init()
{
    // Initialise random number generator
    nrfx_rng_config_t config = NRFX_RNG_DEFAULT_CONFIG;
    return nrfx_rng_init(&config, rng_event_handler);
}

Same thing when using the HW registers directly:

int mcu_rng_generate(int len, uint8_t *rng_buf)
{
    // Reset random number counter
    random_number_index = 0;

    // Setup safety so that RNG does not fill up buffer beyound len
    random_number_max_len = len;
    random_number_buf_ptr = rng_buf;

    /* Configure for bias correction. */
    NRF_RNG->CONFIG = RNG_CONFIG_DERCEN_Enabled << RNG_CONFIG_DERCEN_Pos;

    /* Enable value ready interrupt. */
    NRFX_IRQ_PRIORITY_SET(RNG_IRQn, 6);
    NRFX_IRQ_ENABLE(RNG_IRQn);

    NRF_RNG->INTENSET = RNG_INTENSET_VALRDY_Enabled << RNG_INTENSET_VALRDY_Pos;

    /* Start random number generation. */
    NRF_RNG->TASKS_START = 1U;

    /* Wait for required number of random numbers to be generated. */
    // nrf_delay_ms(1); // <-- THIS WORKS
    while(random_number_index < len); <-- THIS DOES NOT WORK!

    /* Stop random number generator. */
    NRF_RNG->TASKS_STOP = 1U;

    return NRF_SUCCESS;
}


void RNG_IRQHandler(void)
{
    // Clear event
    NRF_RNG->EVENTS_VALRDY = 0U;
    if (random_number_index < random_number_max_len)
    {
        random_number_buf_ptr[random_number_index] = NRF_RNG->VALUE;
        random_number_index++;
    }
}

I have tried setting the NRFX_IRQ_PRIORITY_SET(RNG_IRQn, 6); to different things (0 and 12) but no difference.

Can anybody help explaining what nrf_delay_ms(1); does differently than the busy-waiting version?

Kind regards

[Dmitry]

Hi,

the compiler optimizes (throws away) your busy-wait loop because it has no idea that random_number_index may change outside of this loop. Try to define random_number_index as volatile.

[akofoed]

Thank you very much - it worked.

I must have slept during C-class when volatile was the subject.