circuitpython/ports/stm32/rng.c

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/*
* This file is part of the MicroPython project, http://micropython.org/
*
* The MIT License (MIT)
*
* Copyright (c) 2013-2018 Damien P. George
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
* THE SOFTWARE.
*/
#include "rtc.h"
#include "rng.h"
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#if MICROPY_HW_ENABLE_RNG
#define RNG_TIMEOUT_MS (10)
uint32_t rng_get(void) {
// Enable the RNG peripheral if it's not already enabled
if (!(RNG->CR & RNG_CR_RNGEN)) {
#if defined(STM32H7)
// Set RNG Clock source
__HAL_RCC_PLLCLKOUT_ENABLE(RCC_PLL1_DIVQ);
__HAL_RCC_RNG_CONFIG(RCC_RNGCLKSOURCE_PLL);
#endif
__HAL_RCC_RNG_CLK_ENABLE();
RNG->CR |= RNG_CR_RNGEN;
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}
// Wait for a new random number to be ready, takes on the order of 10us
uint32_t start = HAL_GetTick();
while (!(RNG->SR & RNG_SR_DRDY)) {
if (HAL_GetTick() - start >= RNG_TIMEOUT_MS) {
return 0;
}
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}
// Get and return the new random number
return RNG->DR;
}
// Return a 30-bit hardware generated random number.
STATIC mp_obj_t pyb_rng_get(void) {
return mp_obj_new_int(rng_get() >> 2);
}
MP_DEFINE_CONST_FUN_OBJ_0(pyb_rng_get_obj, pyb_rng_get);
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#else // MICROPY_HW_ENABLE_RNG
// For MCUs that don't have an RNG we still need to provide a rng_get() function,
// eg for lwIP and random.seed(). A pseudo-RNG is not really ideal but we go with
// it for now, seeding with numbers which will be somewhat different each time. We
// don't want to use urandom's pRNG because then the user won't see a reproducible
// random stream.
// Yasmarang random number generator by Ilya Levin
// http://www.literatecode.com/yasmarang
STATIC uint32_t pyb_rng_yasmarang(void) {
static bool seeded = false;
static uint32_t pad = 0, n = 0, d = 0;
static uint8_t dat = 0;
if (!seeded) {
seeded = true;
rtc_init_finalise();
pad = *(uint32_t *)MP_HAL_UNIQUE_ID_ADDRESS ^ SysTick->VAL;
n = RTC->TR;
d = RTC->SSR;
}
pad += dat + d * n;
pad = (pad << 3) + (pad >> 29);
n = pad | 2;
d ^= (pad << 31) + (pad >> 1);
dat ^= (char)pad ^ (d >> 8) ^ 1;
return pad ^ (d << 5) ^ (pad >> 18) ^ (dat << 1);
}
uint32_t rng_get(void) {
return pyb_rng_yasmarang();
}
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#endif // MICROPY_HW_ENABLE_RNG