uint32_t IRAM_ATTR esp_random(void)
{
/* The PRNG which implements WDEV_RANDOM register gets 2 bits
* of extra entropy from a hardware randomness source every APB clock cycle
* (provided WiFi or BT are enabled). To make sure entropy is not drained
* faster than it is added, this function needs to wait for at least 16 APB
* clock cycles after reading previous word. This implementation may actually
* wait a bit longer due to extra time spent in arithmetic and branch statements.
*
* As a (probably unncessary) precaution to avoid returning the
* RNG state as-is, the result is XORed with additional
* WDEV_RND_REG reads while waiting.
*/
/* This code does not run in a critical section, so CPU frequency switch may
* happens while this code runs (this will not happen in the current
* implementation, but possible in the future). However if that happens,
* the number of cycles spent on frequency switching will certainly be more
* than the number of cycles we need to wait here.
*/
uint32_t cpu_to_apb_freq_ratio = esp_clk_cpu_freq() / esp_clk_apb_freq();
static uint32_t last_ccount = 0;
uint32_t ccount;
uint32_t result = 0;
do {
ccount = XTHAL_GET_CCOUNT();
result ^= REG_READ(WDEV_RND_REG);
} while (ccount - last_ccount < cpu_to_apb_freq_ratio * 16);
last_ccount = ccount;
return result ^ REG_READ(WDEV_RND_REG);
}
uint32_t unity_exec_time_get_ms(void)
{
return (s_test_stop - s_test_start) / (esp_clk_cpu_freq() / 1000);
}
