source: rtems/bsps/arm/atsam/start/getentropy-trng.c @ c344e58

/*
 * Copyright (c) 2017 embedded brains GmbH.  All rights reserved.
 *
 *  embedded brains GmbH
 *  Dornierstr. 4
 *  82178 Puchheim
 *  Germany
 *  <rtems@embedded-brains.de>
 *
 * The license and distribution terms for this file may be
 * found in the file LICENSE in this distribution or at
 * http://www.rtems.org/license/LICENSE.
 */

#include <libchip/chip.h>
#include <unistd.h>
#include <string.h>
#include <rtems/sysinit.h>

static void atsam_trng_enable(void)
{
        PMC_EnablePeripheral(ID_TRNG);
        TRNG_Enable();
}

int getentropy(void *ptr, size_t n)
{
        while (n > 0) {
                uint32_t random;
                size_t copy;

                while ((TRNG_GetStatus() & TRNG_ISR_DATRDY) == 0) {
                        /* wait */
                }
                random = TRNG_GetRandData();

                /*
                 * Read TRNG status one more time to avoid race condition.
                 * Otherwise we can read (and clear) an old ready status but get
                 * a new value. The ready status for this value wouldn't be
                 * reset.
                 */
                TRNG_GetStatus();

                copy = sizeof(random);
                if (n < copy ) {
                        copy = n;
                }
                memcpy(ptr, &random, copy);
                n -= copy;
                ptr += copy;
        }

        return 0;
}

RTEMS_SYSINIT_ITEM(
  atsam_trng_enable,
  RTEMS_SYSINIT_DEVICE_DRIVERS,
  RTEMS_SYSINIT_ORDER_LAST_BUT_5
);