esp-idf/components/bootloader_support/src/bootloader_random.c

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/*
* SPDX-FileCopyrightText: 2010-2021 Espressif Systems (Shanghai) CO LTD
*
* SPDX-License-Identifier: Apache-2.0
*/
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#include "sdkconfig.h"
#include "bootloader_random.h"
#include "hal/cpu_hal.h"
#include "soc/wdev_reg.h"
#ifndef BOOTLOADER_BUILD
#include "esp_system.h"
#include "driver/periph_ctrl.h"
__attribute__((weak)) void bootloader_fill_random(void *buffer, size_t length)
{
return esp_fill_random(buffer, length);
}
#else
__attribute__((weak)) void bootloader_fill_random(void *buffer, size_t length)
{
uint8_t *buffer_bytes = (uint8_t *)buffer;
uint32_t random;
uint32_t start, now;
assert(buffer != NULL);
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for (size_t i = 0; i < length; i++) {
if (i == 0 || i % 4 == 0) { /* redundant check is for a compiler warning */
/* in bootloader with ADC feeding HWRNG, we accumulate 1
bit of entropy per 40 APB cycles (==80 CPU cycles.)
To avoid reading the entire RNG hardware state out
as-is, we repeatedly read the RNG register and XOR all
values.
*/
random = REG_READ(WDEV_RND_REG);
start = cpu_hal_get_cycle_count();
do {
random ^= REG_READ(WDEV_RND_REG);
now = cpu_hal_get_cycle_count();
} while (now - start < 80 * 32 * 2); /* extra factor of 2 is precautionary */
}
buffer_bytes[i] = random >> ((i % 4) * 8);
}
}
#ifndef CONFIG_IDF_ENV_FPGA
#else // CONFIG_IDF_ENV_FPGA
#include "esp_log.h"
static void s_non_functional(const char *func)
{
ESP_EARLY_LOGW("rand", "%s non-functional for FPGA builds", func);
}
void bootloader_random_enable()
{
s_non_functional(__func__);
}
void bootloader_random_disable()
{
s_non_functional(__func__);
}
#endif // CONFIG_IDF_ENV_FPGA
#endif // BOOTLOADER_BUILD