stm32_random.c

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/**
 * \file    heivs/stm32_random.c
 * \see     heivs/random.h
 */

#include "heivs/random.h"
#include "stm32/stm32f4xx.h"
#include "stm32/stm32f4xx_rcc.h"
#include "heivs/time.h"

status_e random_init(void)
{
    RCC_AHB2PeriphClockCmd(RCC_AHB2Periph_RNG, ENABLE);
    RCC_AHB2PeriphResetCmd(RCC_AHB2Periph_RNG, ENABLE);
    RCC_AHB2PeriphResetCmd(RCC_AHB2Periph_RNG, DISABLE);

    RNG->CR |= RNG_CR_RNGEN;

    return NO_ERROR;
}

status_e random_suspend(void)
{
    RCC_AHB2PeriphClockCmd(RCC_AHB2Periph_RNG, DISABLE);

    return NO_ERROR;
}

status_e random_get_nowait(uint32_t *data)
{
#if FIPS_140_2
    static uint32_t last = 0;
#endif
    uint32_t sr = RNG->SR;

    *data = 0;

    /* There is an */
    if (sr & (RNG_SR_SECS | RNG_SR_CECS))
    {
        return ERROR_HW_FAILED;
    }

    if (!sr & RNG_SR_DRDY)
    {
        return ERROR_AGAIN;
    }

    *data = RNG->DR;

#if FIPS_140_2
    /**
     * FIPS 140-2
     */
    if (last == *data)
    {
        *data = 0;
        return ERROR_AGAIN;
    }
    last = *data;
#endif

    return NO_ERROR;
}

status_e random_get(uint32_t *data, uint32_t timeout_ms)
{
    timeout_t timeout = time_set_timeout_ms(timeout_ms);

    *data = 0;

    while (1)
    {
        status_e status = random_get_nowait(data);

        switch (status)
        {
        case NO_ERROR:
            return status;
        break;

        case ERROR_HW_FAILED:
            /* status will be checked on the next loop */
            (void)random_init();
        break;

        case ERROR_AGAIN:
        break;

        default:
            return ERROR_BAD_STATE;
        break;
        }

        if (time_elapsed(timeout))
        {
            return ERROR_TIMEOUT;
        }
    }

    return ERROR_BAD_STATE;
}