ascon-trng-due.c

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/*
 * Copyright (C) 2022 Southern Storm Software, Pty Ltd.
 *
 * Permission is hereby granted, free of charge, to any person obtaining a
 * copy of this software and associated documentation files (the "Software"),
 * to deal in the Software without restriction, including without limitation
 * the rights to use, copy, modify, merge, publish, distribute, sublicense,
 * and/or sell copies of the Software, and to permit persons to whom the
 * Software is furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included
 * in all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
 * OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
 * DEALINGS IN THE SOFTWARE.
 */
 
#include "ascon-trng.h"
#include <string.h>
 
#if defined(ASCON_TRNG_DUE)
 
#include <Arduino.h>
 
static int volatile due_init_done = 0;
 
static inline void ascon_trng_init_internal(void)
{
    if (!due_init_done) {
        /* Once-only initialization of the TRNG peripheral */
        pmc_enable_periph_clk(ID_TRNG);
        REG_TRNG_CR = TRNG_CR_KEY(0x524E47) | TRNG_CR_ENABLE;
        REG_TRNG_IDR = TRNG_IDR_DATRDY;
        due_init_done = 1;
    }
}
 
static inline int ascon_trng_generate_word(uint32_t *x)
{
    /* SAM3X8E's TRNG returns a new random word every 84 clock cycles.
     * If the TRNG is not ready after 100 iterations, assume it has failed. */
    int count = 100;
    while ((REG_TRNG_ISR & TRNG_ISR_DATRDY) == 0) {
        if ((--count) <= 0) {
            *x = 0xABADBEEF; /* This is a problem! */
            return 0;
        }
    }
    *x = REG_TRNG_ODATA;
    return 1;
}
 
int ascon_trng_generate(unsigned char *out, size_t outlen)
{
    uint32_t x;
    int ok = 1;
    ascon_trng_init_internal();
    while (outlen >= sizeof(x)) {
        if (!ascon_trng_generate_word(&x))
            ok = 0;
        memcpy(out, &x, sizeof(x));
        out += sizeof(x);
        outlen -= sizeof(x);
    }
    if (outlen > 0) {
        if (!ascon_trng_generate_word(&x))
            ok = 0;
        memcpy(out, &x, outlen);
    }
    return ok;
}
 
int ascon_trng_init(ascon_trng_state_t *state)
{
    uint32_t x;
 
    /* Make sure that the peripheral is initialized */
    ascon_trng_init_internal();
 
    /* Test that the TRNG works by generating a single word */
    return ascon_trng_generate_word(&x);
}
 
void ascon_trng_free(ascon_trng_state_t *state)
{
    (void)state;
}
 
uint32_t ascon_trng_generate_32(ascon_trng_state_t *state)
{
    uint32_t word;
    (void)state;
    ascon_trng_generate_word(&word);
    return word;
}
 
uint64_t ascon_trng_generate_64(ascon_trng_state_t *state)
{
    uint32_t low, high;
    (void)state;
    ascon_trng_generate_word(&low);
    ascon_trng_generate_word(&high);
    return ((uint64_t)low) | (((uint64_t)high) << 32);
}
 
int ascon_trng_reseed(ascon_trng_state_t *state)
{
    return ascon_trng_init(state);
}
 
#endif /* ASCON_TRNG_DUE */