undefined reference to `nrf_drv_rng_init'

Hi, 

I am using Segger IDE.

I encounter error undefined reference to `nrf_drv_rng_init' .

I have include the below header file;

#include "nrf_drv_rng.h"

I already enable  below macro;

#ifndef RNG_ENABLED
#define RNG_ENABLED 1
#endif

#ifndef NRFX_RNG_ENABLED
#define NRFX_RNG_ENABLED 1
#endif

What is missing ?

Thanks.