Using the random number generator with SDK 15.3

[bojerko]

I am trying to use RNG HAL  but I am not sure how to use it and there are (as far as I can tell) no examples. The only thing I need is generating random number. So I'm not using any cryptography, but just need simple random number.

I wrote the code like that:

nrf_rng_task_trigger(NRF_RNG_TASK_SET);
uint8_t value = nrf_rng_random_value_get();

But apparently I'm missing something. I have also added #define RNG_ENABLED 1 to sdk_config.h

Any suggestions what to do?

Thanks.

[Jimmy Wong]

You can refer to the sdk example (SDK15.3\examples\crypto\nrf_crypto\rng) or SDK15.3\examples\peripheral\rng.

    err_code = nrf_drv_rng_init(NULL);
    APP_ERROR_CHECK(err_code);

    NRF_LOG_INFO("RNG example started.");

    while (true)
    {
        uint8_t p_buff[RANDOM_BUFF_SIZE];
        uint8_t length = random_vector_generate(p_buff,RANDOM_BUFF_SIZE);
        NRF_LOG_INFO("Random Vector:");
        NRF_LOG_HEXDUMP_INFO(p_buff, length);
        NRF_LOG_INFO("");
        NRF_LOG_FLUSH();
        nrf_delay_ms(100);
    }

[bojerko]

Isn't that a legacy way of doing random numbers? 

[Jimmy Wong]

You can use the nRF Thingy as the reference by using the nrf_drv_rng module.

https://github.com/NordicSemiconductor/Nordic-Thingy52-FW

static uint32_t random_vector_generate(uint8_t * p_buff, uint8_t size)
{
    uint32_t err_code;
    uint8_t  bytes_available = 0;

    nrf_drv_rng_bytes_available(&bytes_available);
    uint8_t retries = 0;
    
    while (bytes_available < size)
    {
        retries++;
        NRF_LOG_WARNING("Too few random bytes available. Trying again \r\n");
        nrf_drv_rng_bytes_available(&bytes_available);
        nrf_delay_ms(5);
        
        if (retries > 5)    // Return after n attempts.
        {
            return NRF_ERROR_TIMEOUT;
        }
    }
    
    NRF_LOG_INFO("Available random bytes: %d \r\n", bytes_available);

    err_code = nrf_drv_rng_rand(p_buff, size);
    RETURN_IF_ERROR(err_code);
    
    NRF_LOG_INFO("Random value (hex): ");
    
    for (uint8_t i = 0; i < size; i++)
    {
        NRF_LOG_RAW_INFO("%02x", p_buff[i]);
    }
    
    NRF_LOG_RAW_INFO("\r\n");

    return NRF_SUCCESS;
}

[bojerko]

This is also a legacy way of doing it. In SDK 15 the new way was introduced by using nrfx_rng.h.

There are some macros here https://infocenter.nordicsemi.com/topic/com.nordic.infocenter.sdk5.v15.3.0/group__nrf__rng__hal.html

That's what I would like to use to avoid legacy code.

[bojerko]

Found the error in the code. The proper way is to use:

nrf_rng_task_trigger(NRF_RNG_TASK_START);
uint8_t value = nrf_rng_random_value_get();

So I made a mistake and used NRF_RNG_TASK_SET instead of NRF_RNG_TASK_START.

It works now.