raspi3-tutorial/06_random/rand.c

/*
 * Copyright (C) 2018 bzt (bztsrc@github)
 *
 * 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 "gpio.h"

#define RNG_CTRL        ((volatile unsigned int*)(MMIO_BASE+0x00104000))
#define RNG_STATUS      ((volatile unsigned int*)(MMIO_BASE+0x00104004))
#define RNG_DATA        ((volatile unsigned int*)(MMIO_BASE+0x00104008))
#define RNG_INT_MASK    ((volatile unsigned int*)(MMIO_BASE+0x00104010))

/**
 * Initialize the RNG
 */
void rand_init()
{
    *RNG_STATUS=0x40000;
    // mask interrupt
    *RNG_INT_MASK|=1;
    // enable
    *RNG_CTRL|=1;
}

/**
 * Return a random number between [min..max]
 */
unsigned int rand(unsigned int min, unsigned int max)
{
    // may need to wait for entropy: bits 24-31 store how many words are
    // available for reading; require at least one
    while(!((*RNG_STATUS)>>24)) asm volatile("nop");
    return *RNG_DATA % (max-min) + min;
}