hwrng.c
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/*
* Copyright (C) 2014-2016 Freie Universität Berlin
*
* This file is subject to the terms and conditions of the GNU Lesser
* General Public License v2.1. See the file LICENSE in the top level
* directory for more details.
*/
/**
* @ingroup cpu_sam3
* @{
*
* @file
* @brief Low-level random number generator driver implementation
*
* @author Hauke Petersen <hauke.petersen@fu-berlin.de>
*
* @}
*/
#include "cpu.h"
#include "periph/hwrng.h"
/**
* @name KEY needs to be written to the config register when en|disabling
* random number generation
*/
#define KEY (0x524e4700)
void hwrng_init(void)
{
/* no need for initialization */
}
void hwrng_read(uint8_t *buf, unsigned int num)
{
unsigned count = 0;
/* enable clock signal for TRNG module */
PMC->PMC_PCER1 |= PMC_PCER1_PID41;
/* enable the generation of random numbers */
TRNG->TRNG_CR |= (KEY | TRNG_CR_ENABLE);
while (count < num) {
/* wait until new value is generated -> takes up to 84 cycles */
while (!(TRNG->TRNG_ISR & TRNG_ISR_DATRDY)) {}
/* read 4 byte of random data */
uint32_t tmp = TRNG->TRNG_ODATA;
/* extract copy bytes to result */
for (int i = 0; i < 4 && count < num; i++) {
buf[count++] = (uint8_t)tmp;
tmp = tmp >> 8;
}
}
/* disable the generation of random numbers */
TRNG->TRNG_CR &= ~(KEY | TRNG_CR_ENABLE);
/* disable clock signal for TRNG module */
PMC->PMC_PCER1 &= ~(PMC_PCER1_PID41);
}