atsam/start/getentropy-trng.c

0001 /* SPDX-License-Identifier: BSD-2-Clause */
0002
0003 /*
0004  * Copyright (c) 2017 embedded brains GmbH & Co. KG
0005  *
0006  * Redistribution and use in source and binary forms, with or without
0007  * modification, are permitted provided that the following conditions
0008  * are met:
0009  * 1. Redistributions of source code must retain the above copyright
0010  *    notice, this list of conditions and the following disclaimer.
0011  * 2. Redistributions in binary form must reproduce the above copyright
0012  *    notice, this list of conditions and the following disclaimer in the
0013  *    documentation and/or other materials provided with the distribution.
0014  *
0015  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
0016  * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
0017  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
0018  * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
0019  * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
0020  * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
0021  * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
0022  * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
0023  * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
0024  * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
0025  * POSSIBILITY OF SUCH DAMAGE.
0026  */
0027
0028 #include <libchip/chip.h>
0029 #include <unistd.h>
0030 #include <string.h>
0031 #include <rtems/sysinit.h>
0032
0033 static void atsam_trng_enable(void)
0034 {
0035     PMC_EnablePeripheral(ID_TRNG);
0036     TRNG_Enable();
0037 }
0038
0039 int getentropy(void *ptr, size_t n)
0040 {
0041     while (n > 0) {
0042         uint32_t random;
0043         size_t copy;
0044
0045         while ((TRNG_GetStatus() & TRNG_ISR_DATRDY) == 0) {
0046             /* wait */
0047         }
0048         random = TRNG_GetRandData();
0049
0050         /*
0051          * Read TRNG status one more time to avoid race condition.
0052          * Otherwise we can read (and clear) an old ready status but get
0053          * a new value. The ready status for this value wouldn't be
0054          * reset.
0055          */
0056         TRNG_GetStatus();
0057
0058         copy = sizeof(random);
0059         if (n < copy ) {
0060             copy = n;
0061         }
0062         memcpy(ptr, &random, copy);
0063         n -= copy;
0064         ptr += copy;
0065     }
0066
0067     return 0;
0068 }
0069
0070 RTEMS_SYSINIT_ITEM(
0071   atsam_trng_enable,
0072   RTEMS_SYSINIT_DEVICE_DRIVERS,
0073   RTEMS_SYSINIT_ORDER_LAST_BUT_5
0074 );