issue with NRF RNG generator

[Anjali]

hi,

I am working with nr52832 and SDK 12.1. I have referred the RNG example based on which I have integrated that code section in my custom application:

     rng_generate(rand_arr1, RAND_STREAM_BYTES); //example output: 15234
     rng_generate(rand_arr2, RAND_STREAM_BYTES); //15234

    ... user generated delay

    rng_generate(rand_arr1, RAND_STREAM_BYTES); //23145
    rng_generate(rand_arr2, RAND_STREAM_BYTES); //23145

and the code for rng_generate is:

void rng_generate(uint8_t *rand_arr, uint8_t len)
{
  //nrf_drv_rng_config_t rand_config;
  uint8_t bytes_avail;
  uint32_t err_code;
  err_code = nrf_drv_rng_bytes_available(&bytes_avail);
  APP_ERROR_CHECK(err_code);
  uint8_t length = (len<bytes_avail) ? len : bytes_avail;
  err_code = nrf_drv_rng_rand(rand_arr,length);
  APP_ERROR_CHECK(err_code);

}

I have initialised rng in main. My issue is: When I call the rng_generate twice immediately, I get the same number in rand_arr1 and rnad_arr2. This number changes after some user-generated delay is included (which is huge). But again if there are two immediate calls to rng_generate, I get the same number. I tried to include a few ms delay between them, but the results were same. How can I avoid this issue? Or is than any alternate api for generating true non-deterministic random numbers?

Thanks

[Jørgen Holmefjord]

Hi,

Are you using a softdevice? If you are, you should use the softdevice functions:

sd_rand_application_bytes_available_get

sd_rand_application_pool_capacity_get

sd_rand_application_vector_get

If you are not using a softdevice, you can try the blocking function nrf_drv_rng_block_rand. Do you get the same result if you call rng_generate more than two times? How many times before it change?

Best regards,

Jørgen

[Anjali]

Ok, I will use the soft device api, and test again with UART logging. Thank you