mirror of
https://github.com/espressif/esp-idf.git
synced 2025-10-26 04:31:43 +01:00
70 lines
2.5 KiB
C
70 lines
2.5 KiB
C
// Copyright 2016 Espressif Systems (Shanghai) PTE LTD
|
|
//
|
|
// Licensed under the Apache License, Version 2.0 (the "License");
|
|
// you may not use this file except in compliance with the License.
|
|
// You may obtain a copy of the License at
|
|
//
|
|
// http://www.apache.org/licenses/LICENSE-2.0
|
|
//
|
|
// Unless required by applicable law or agreed to in writing, software
|
|
// distributed under the License is distributed on an "AS IS" BASIS,
|
|
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
|
|
// See the License for the specific language governing permissions and
|
|
// limitations under the License.
|
|
|
|
|
|
#include <stdint.h>
|
|
#include <stddef.h>
|
|
#include <string.h>
|
|
#include <sys/param.h>
|
|
#include "esp_attr.h"
|
|
#include "hal/cpu_hal.h"
|
|
#include "esp32/clk.h"
|
|
#include "soc/wdev_reg.h"
|
|
|
|
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 = cpu_hal_get_cycle_count();
|
|
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);
|
|
}
|
|
|
|
void esp_fill_random(void *buf, size_t len)
|
|
{
|
|
assert(buf != NULL);
|
|
uint8_t *buf_bytes = (uint8_t *)buf;
|
|
while (len > 0) {
|
|
uint32_t word = esp_random();
|
|
uint32_t to_copy = MIN(sizeof(word), len);
|
|
memcpy(buf_bytes, &word, to_copy);
|
|
buf_bytes += to_copy;
|
|
len -= to_copy;
|
|
}
|
|
}
|