libhydrogen/impl/random/stm32.h

// Use hardware RNG peripheral
// Working with HAL, LL Driver (untested)

#ifdef STM32F4

#include "stm32f4xx.h"

static int
hydro_random_init(void)
{
    const char       ctx[hydro_hash_CONTEXTBYTES] = { 'h', 'y', 'd', 'r', 'o', 'P', 'R', 'G' };
    hydro_hash_state st;
    uint16_t         ebits = 0;

    __IO uint32_t tmpreg;

    // Enable RNG clock source
    SET_BIT(RCC->AHB2ENR, RCC_AHB2ENR_RNGEN);

    // Delay after an RCC peripheral clock enabling
    tmpreg = READ_BIT(RCC->AHB2ENR, RCC_AHB2ENR_RNGEN);
    UNUSED(tmpreg);

    // RNG Peripheral enable
    SET_BIT(RNG->CR, RNG_CR_RNGEN);

    hydro_hash_init(&st, ctx, NULL);

    while (ebits < 256) {
        while (!(READ_BIT(RNG->SR, RNG_SR_DRDY))) {
        }

        uint32_t r = RNG->DR;
        hydro_hash_update(&st, (const uint32_t*) &r, sizeof r);
        ebits += 32;
    }

    hydro_hash_final(&st, hydro_random_context.state, sizeof hydro_random_context.state);
    hydro_random_context.counter = ~LOAD64_LE(hydro_random_context.state);

    return 0;
}

#else
# error SMT32 implementation missing!
#endif