I meet a problem when I call function `psa_crypto_init`, it return error code -148 that was PSA_ERROR_INSUFFICIENT_ENTROPY.

I track this function step by step and found it caused by MBEDTLS_ERR_ENTROPY_NO_SOURCES_DEFINED. Code in entropy.c, if( ctx->source_count == 0 ), return this error.

My question:

I run code on Ubuntu, it runs well. But in some arm board, it returns this error. Why this count will be 0 sometimes? What is the root cause of this error.