lora-irrigation/board/strobe_f1_rng_init.c

/*-
 * Copyright 2021 John-Mark Gurney.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 */

#include <strobe.h>

#include <board/simpflash.h>
#include <strobe_rng_init.h>

#include "stm32f1xx.h"
#include "stm32f1xx_hal.h"

#include <stm32f1xx_hal_adc.h>

#include <sysinit.h>

#include <unistd.h>

#define NBYTESENTROPY	(256 / 8)
#define DEFINE_RNG_SAVE	1
#if DEFINE_RNG_SAVE
const rng_word_t rng_save[roundup(NBYTESENTROPY, sizeof(rng_word_t)) / sizeof(rng_word_t)] __attribute__ ((section (".savestate")));
#endif

static void
strobe_rng_init(void)
{

	/*
	 * Seed RNG
	 * Seed w/ saved state.
	 */
	strobe_seed_prng((uint8_t *)rng_save, sizeof rng_save);

	/*
	 * On first boot, SRAM is uninitialized and randomness from
	 * it is used.
	 *
	 * Note: This depends upon sbrk pointing to uinitalized SRAM.
	 */
	strobe_seed_prng(sbrk(0), 2*1024);

}
SYSINIT_VF(rng_init, SI_SUB_HAL, SI_ORDER_LAST, strobe_rng_init);

uint32_t times[20];

static void
analog_seed_rng(void)
{
	ADC_HandleTypeDef ah;
	ADC_ChannelConfTypeDef	chanconf;
	uint16_t v;
	int timespos;
	int i;

	/* Enable ADC1 Clock */
	__HAL_RCC_ADC1_CLK_ENABLE();

	/* Configure */
	ah = (ADC_HandleTypeDef){
		.Instance			= ADC1,
		.Init.DataAlign			= ADC_DATAALIGN_RIGHT,
		.Init.ScanConvMode		= ADC_SCAN_DISABLE,
		.Init.ContinuousConvMode	= DISABLE,
		.Init.NbrOfConversion		= 1,
		.Init.DiscontinuousConvMode	= DISABLE,
		.Init.NbrOfDiscConversion	= 1,
		.Init.ExternalTrigConv		= ADC_SOFTWARE_START,
	};
	HAL_ADC_Init(&ah);

	chanconf = (ADC_ChannelConfTypeDef){
		.Rank = ADC_REGULAR_RANK_1,
		.Channel = ADC_CHANNEL_TEMPSENSOR,	/* temp sensor */
		.SamplingTime = ADC_SAMPLETIME_71CYCLES_5,
	};
	HAL_ADC_ConfigChannel(&ah, &chanconf);

	HAL_Delay(1);

	timespos = 0;

	/* Capture */
	for (i = 0; i < 256 / 2; i++) {
		times[timespos++] = HAL_GetTick();
		timespos %= sizeof times / sizeof *times;
		/*
		 * Capture some ADC data.  If pin is floating, 0xfff
		 * happens frequently, if pin is grounded, 0 happens
		 * frequently, filter these values out.
		 */
		do {
			HAL_ADC_Start(&ah);
			HAL_ADC_PollForConversion(&ah, 1);
			v = HAL_ADC_GetValue(&ah);
		} while (v == 0 || v == 0xfff);
		strobe_seed_prng((uint8_t *)&v, sizeof v);
	}

	/* Deinit */
	HAL_ADC_DeInit(&ah);
}
SYSINIT_VF(analog_seed_rng, SI_SUB_HAL, SI_ORDER_LAST, analog_seed_rng);

static void
strobe_rng_save(void)
{
	rng_word_t tmp[sizeof rng_save / sizeof(rng_word_t)];
	int r;

	/*
	 * Save entropy for next reset.
	 */
	r = strobe_randomize((uint8_t *)tmp, sizeof tmp);
	(void)r;

	doflash(rng_save, tmp, sizeof(rng_save));
}
SYSINIT_VF(rng_save, SI_SUB_LAST, SI_ORDER_LAST, strobe_rng_save);