RNG with CC310 Library Causing Board Watch Dog Reset.

[Srinivas V]

Hi Team,

We are using the nRF52840 DK for one of our project, as part of that we are using the RNG functionality with CC310 Library.

When we call this "CRYS_RND_GenerateVector" function at fixed interval like for every 6 or 5 sec, over the period of time board is getting the WDT Reset.

Could any one help me out what is causing this issue, I have shared the code snippet as well for this. 

1. Is there any way we can generate the RNG without using the CC310 Library like by using the any SW dependent library.

2. Is there any Dependency between CC310 RNG and WDT Peripherals.

How best we can use the RNG functionalities by using any library for nRF52840 Apart from CC310.

Regards,

Srinivas.V

uint32_t rng_vector_generate(uint8_t * const p_target, uint8_t size)
{
uint8_t rndTest_AddInputData[RANDOM_BUFF_SIZE] = {0x00,0x01,0x02,0x03,0x04,0x05,0x06,0x07,0x08,0x09,0x0A,0x0B,0x0C,0x0D,0x0E,0x0F};
  rndState_ptr = &rndState;
  rndWorkBuff_ptr = &rndWorkBuff;
   
  NVIC_EnableIRQ(CRYPTOCELL_IRQn);
  NRF_CRYPTOCELL->ENABLE = 1;
  
    /*Init SaSi library*/
    ret = SaSi_LibInit();
    
    if (ret != SA_SILIB_RET_OK) 
    {
        return ret;
    }

  ret = CRYS_RndInit(rndState_ptr, rndWorkBuff_ptr);
     
   if (ret != SA_SILIB_RET_OK)
   {
      return ret;
   }
    
  /*Generate random vector 1*/
   ret = CRYS_RND_GenerateVector(rndState_ptr,RANDOM_BUFF_SIZE, p_target);	
        
   if ((ret != SA_SILIB_RET_OK) && (ret == CRYS_RND_RESEED_COUNTER_OVERFLOW_ERROR ))
   {
     
      /*Set additional input for rng seed*/
      ret = CRYS_RND_AddAdditionalInput(rndState_ptr, rndTest_AddInputData, 16);
		
      if (ret != SA_SILIB_RET_OK)
      {
          return ret;
      }
      
      /*Reseed rnd using added input (new seed will be generated using additional input)*/
	ret = CRYS_RND_Reseeding(rndState_ptr, rndWorkBuff_ptr);
	
      if (ret != SA_SILIB_RET_OK)
      {
            return ret;
      }
      
      ret = CRYS_RND_GenerateVector(rndState_ptr,RANDOM_BUFF_SIZE, p_target);
      
      if (ret != SA_SILIB_RET_OK)
      {
            return ret;
      }
   }
    
    SaSi_LibFini();
     
    // Disable the CryptoCell IRQ
    NVIC_DisableIRQ(CRYPTOCELL_IRQn);
    NRF_CRYPTOCELL->ENABLE = 0;
    ret = CRYS_RND_UnInstantiation(rndState_ptr);
}

[Kenneth]

There is no dependency between CC310 and WDT, can it simply be because you are using a very short reload of the watchdog timeout, such that it resets because it's not reloaded?

Kenneth

[Srinivas V]

Hi Kenneth,

Thanks for your reply.

We have configured the WDT with time delay of 13sec. But it is not due to RNG is taking more time, but we continuously hitting the " SaSi_HalWaitInterrupt" this handler and from this Watchdog Reset is occurring.

Can you suggest any other driver which is having the less complexity compared to CC310.

Regards,

Srinivas.V

[Kenneth]

If you need random generated numbers you can also use the RNG module:
https://infocenter.nordicsemi.com/topic/ps_nrf52840/rng.html
https://infocenter.nordicsemi.com/topic/sdk_nrf5_v17.0.2/hardware_driver_rng.html

The only thing you need to make sure is to enable BIAS correction in CONFIG register. The RNG module is the same as used by the BLE softdevice implementation, so it satisfy the requirements to RNG by the BLE core specification. If the softdevice is enabled you need to use the softdevice api to get the RNG values (then BIAS correction is already enabled).

Best regards,
Kenneth