reflow-oven-control-sw/stm-firmware/safety/watchdog.c

/* Reflow Oven Controller
*
* Copyright (C) 2020  Mario Hüttel <mario.huettel@gmx.net>
*
* This file is part of the Reflow Oven Controller Project.
*
* The reflow oven controller is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License version 2 as
* published by the Free Software Foundation.
*
* The Reflow Oven Control Firmware is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with the reflow oven controller project.
* If not, see <http://www.gnu.org/licenses/>.
*/

/**
 * @addtogroup watchdog
 * @{
 */

#include <reflow-controller/safety/watchdog.h>
#include <stm32/stm32f4xx.h>

/**
 * @brief This key is expected by hardware to be written to the IWDG_KR register in order to reset the watchdog
 */
#define STM32_WATCHDOG_RESET_KEY 0xAAAA

/**
 * @brief This key is expected by hardware to be written to the IWDG_KR register in order to enable the watchdog
 */
#define STM32_WATCHDOG_ENABLE_KEY 0xCCCC

/**
 * @brief This key is expected by hardware to be written to the IWDG_KR register in order to enable access to config
 * registers
 */
#define STM32_WATCHDOG_REGISTER_ACCESS_KEY 0x5555

int watchdog_setup(uint8_t prescaler)
{
	uint32_t prescaler_reg_val;

	/** - Activate the LSI oscillator */
	RCC->CSR |= RCC_CSR_LSION;
	__DSB();
	/** - Wait for the oscillator to be ready */
	while (!(RCC->CSR & RCC_CSR_LSIRDY));

	if (prescaler == 4U)
		prescaler_reg_val = 0UL;
	else if (prescaler == 8U)
		prescaler_reg_val = 1UL;
	else if (prescaler == 16U)
		prescaler_reg_val = 2UL;
	else if (prescaler == 32U)
		prescaler_reg_val = 3UL;
	else if (prescaler == 64U)
		prescaler_reg_val = 4UL;
	else if (prescaler == 128U)
		prescaler_reg_val = 5UL;
	else
		prescaler_reg_val = 6UL;

	/** - Unlock registers */
	IWDG->KR = STM32_WATCHDOG_REGISTER_ACCESS_KEY;

	/** - Wait until prescaler can be written */
	while (IWDG->SR & IWDG_SR_PVU);

	/** - Write prescaler value */
	IWDG->PR = prescaler_reg_val;

	/* - Wait until reload value can be written */
	while (IWDG->SR & IWDG_SR_RVU);

	/** - Set reload value fixed to 0xFFF */
	IWDG->RLR = 0xFFFU;

	/** - Write enable key */
	IWDG->KR = STM32_WATCHDOG_ENABLE_KEY;

	/** - Do a first reset of the counter. This also locks the config regs */
	watchdog_ack(WATCHDOG_MAGIC_KEY);

	return 0;
}

int watchdog_ack(uint32_t magic)
{
	int ret = -1;

	/** - Check if magic key is correct */
	if (magic == WATCHDOG_MAGIC_KEY) {
		/** - Write reset key to watchdog */
		IWDG->KR = STM32_WATCHDOG_RESET_KEY;
		ret = 0;
	}

	return ret;
}

/** @} */