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7adb50b901
If the ADC SAR is used, the Bootloader RNG must not be enabled before the random numbers are actually required. The reason is that the Bootloader RNG uses the noise of the ADC SAR reference voltage as a non-RF entropy source. The calibration of the ADC SAR does not work correctly in this case. Therefore, the Bootloader RNG is only enabled if random numbers are really required.
68 lines
1.9 KiB
C
68 lines
1.9 KiB
C
/*
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* Copyright (C) 2019 Gunar Schorcht
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*
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* This file is subject to the terms and conditions of the GNU Lesser
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* General Public License v2.1. See the file LICENSE in the top level
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* directory for more details.
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*/
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/**
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* @ingroup cpu_esp32
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* @ingroup drivers_periph_hwrng
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* @{
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*
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* @file
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* @brief Low-level random number generator driver implementation for ESP32x SoCs
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*
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* @author Gunar Schorcht <gunar@schorcht.net>
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*
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* @}
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*/
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#include "cpu.h"
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#include "periph_conf.h"
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#include "periph/hwrng.h"
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#include "bootloader_random.h"
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#include "esp_random.h"
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void hwrng_init(void)
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{
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/* If the ADC SAR is used, the Bootloader RNG must not be enabled before
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* the random numbers are actually required. The reason is that the
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* Bootloader RNG uses the noise of the ADC SAR reference voltage as
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* a non-RF entropy source. The calibration of the ADC SAR does not
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* work correctly in this case. Therefore, the Bootloader RNG is only
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* enabled if random numbers are really required. */
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}
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/**
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* The RNG implementation of the ESP-IDF also uses the hardware RNG register
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* RNG_DATA_REG (WDEV_RND_REG) for random number generation, which adds 2 bits
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* of entropy at each APB clock cycle when WiFi or BT are enabled. However,
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* it ensures that the random numbers are not read faster than generated
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* in hardware by including some busy waiting. We therefore use this
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* implementation here.
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*/
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void hwrng_read(void *buf, unsigned int num)
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{
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if (!IS_USED(MODULE_ESP_WIFI_ANY) && !IS_USED(MODULE_ESP_BLE)) {
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/* enable the Bootloader RNG if WiFi and BT are not used */
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bootloader_random_enable();
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}
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esp_fill_random(buf, num);
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if (!IS_USED(MODULE_ESP_WIFI_ANY) && !IS_USED(MODULE_ESP_BLE)) {
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/* disable the Bootloader RNG to ensure that ADC SAR calibration works */
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bootloader_random_disable();
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}
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}
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uint32_t hwrand(void)
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{
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uint32_t rand;
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hwrng_read(&rand, 4);
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return rand;
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}
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