stm32f1/application.c

/* This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program 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 this program.  If not, see <http://www.gnu.org/licenses/>.
 *
 */
/** sound level enforcer
 *  @file
 *  @author King Kévin <kingkevin@cuvoodoo.info>
 *  @date 2016-2020
 */

/* standard libraries */
#include <stdint.h> // standard integer types
#include <stdlib.h> // standard utilities
#include <string.h> // string utilities
#include <time.h> // date/time utilities
#include <ctype.h> // utilities to check char
#include <math.h> // for rounding floats

/* STM32 (including CM3) libraries */
#include <libopencmsis/core_cm3.h> // Cortex M3 utilities
#include <libopencm3/cm3/scb.h> // vector table definition
#include <libopencm3/cm3/nvic.h> // interrupt utilities
#include <libopencm3/stm32/gpio.h> // general purpose input output library
#include <libopencm3/stm32/rcc.h> // real-time control clock library
#include <libopencm3/stm32/exti.h> // external interrupt utilities
#include <libopencm3/stm32/rtc.h> // real time clock utilities
#include <libopencm3/stm32/iwdg.h> // independent watchdog utilities
#include <libopencm3/stm32/dbgmcu.h> // debug utilities
#include <libopencm3/stm32/desig.h> // design utilities
#include <libopencm3/stm32/flash.h> // flash utilities

/* own libraries */
#include "global.h" // board definitions
#include "print.h" // printing utilities
#if !defined(STLINKV2)
#include "uart.h" // USART utilities
#endif
#include "usb_cdcacm.h" // USB CDC ACM utilities
#include "terminal.h" // handle the terminal interface
#include "menu.h" // menu utilities
#include "led_tm1637.h" // 7-segment display
#include "spp_rx.h" // Bluetooth SPP input
#include "flash_internal.h" // settings storage

/** watchdog period in ms */
#define WATCHDOG_PERIOD 10000

/** set to 0 if the RTC is reset when the board is powered on, only indicates the uptime
 *  set to 1 if VBAT can keep the RTC running when the board is unpowered, indicating the date and time
 */
#if defined(CORE_BOARD)
#define RTC_DATE_TIME 1
#else
#define RTC_DATE_TIME 0
#endif

/** number of RTC ticks per second
 *  @note use integer divider of oscillator to keep second precision
 */
#define RTC_TICKS_SECOND 4

/** RTC time when device is started */
static time_t time_start = 0;

/** @defgroup main_flags flag set in interrupts to be processed in main task
 *  @{
 */
volatile bool rtc_internal_tick_flag = false; /**< flag set when internal RTC ticked */
/** @} */

/** buffer for the data received over Bluetooth from the sound level meter */
static char spp_input_buffer[16];
/** how much received data is buffered */
static uint8_t spp_input_i = 0;

/** pin to control relay (active low) */
#define RELAY_PIN PB15

/** default sound level threshold (in dBa) */
#define SOUND_LEVEL_THRESHOLD 100
/** configured sound level threshold (in dBa) */
static uint8_t sound_level_threshold = SOUND_LEVEL_THRESHOLD;
/** default sound level duration (in seconds) */
#define SOND_LEVEL_DURATION 10
/** configured sound level duration (in seconds) */
static uint8_t sound_level_duration = SOND_LEVEL_DURATION;
/** if we show the received sound level value */
static bool sound_level_show = false;

size_t putc(char c)
{
	size_t length = 0; // number of characters printed
	static char last_c = 0; // to remember on which character we last sent
	if ('\n' == c) { // send carriage return (CR) + line feed (LF) newline for each LF
		if ('\r' != last_c) { // CR has not already been sent
#if !defined(STLINKV2)
			uart_putchar_nonblocking('\r'); // send CR over USART
#endif
			usb_cdcacm_putchar('\r'); // send CR over USB
			length++; // remember we printed 1 character
		}
	}
#if !defined(STLINKV2)
	uart_putchar_nonblocking(c); // send byte over USART
#endif
	usb_cdcacm_putchar(c); // send byte over USB
	length++; // remember we printed 1 character
	last_c = c; // remember last character
	return length; // return number of characters printed
}

/** display available commands
 *  @param[in] argument no argument required
 */
static void command_help(void* argument);

/** show software and hardware version
 *  @param[in] argument no argument required
 */
static void command_version(void* argument);

/** show uptime
 *  @param[in] argument no argument required
 */
static void command_uptime(void* argument);

#if RTC_DATE_TIME
/** show date and time
 *  @param[in] argument date and time to set
 */
static void command_datetime(void* argument);
#endif

/** reset board
 *  @param[in] argument no argument required
 */
static void command_reset(void* argument);

/** switch to DFU bootloader
 *  @param[in] argument no argument required
 */
static void command_bootloader(void* argument);

/** load sound level threshold and duration settings from flash
 *  @return if values are loaded from flash (else set to default)
 */
static bool sound_level_load(void)
{
	uint8_t eeprom_data[4] = {0};
	const bool eeprom_read = flash_internal_eeprom_read(eeprom_data, sizeof(eeprom_data));
	if (eeprom_read) {
		eeprom_data[1] ^= 0xff; // xor value (sort of checksum)
		eeprom_data[3] ^= 0xff; // xor value (sort of checksum)
		if (eeprom_data[0] == eeprom_data[1] && eeprom_data[2] == eeprom_data[3]) {
			sound_level_threshold = eeprom_data[0];
			sound_level_duration = eeprom_data[2];
			return true;
		} else {
			return false;
		}
	} else {
		sound_level_threshold = SOUND_LEVEL_THRESHOLD;
		sound_level_duration = SOND_LEVEL_DURATION;
		return false;
	}
}

/** save sound level threshold and duration settings into flash
 *  @return if succeeded
 */
static bool sound_level_save(void)
{
	const uint8_t eeprom_data[4] = {
		sound_level_threshold,
		sound_level_threshold ^ 0xff,
		sound_level_duration,
		sound_level_duration ^ 0xff,
	};
	const int32_t rc = flash_internal_eeprom_write(eeprom_data, sizeof(eeprom_data));
	if (rc < 0) {
		printf("error saving sound level data: %d\n", rc);
	}

	return rc == sizeof(eeprom_data);
}

/** set sound level threshold
 *  @param[in] argument sound level threshold
 */
static void command_sound_level_threshold(void* argument)
{
	if (argument) { // tachometer value has been provided
		const uint32_t value = *(uint32_t*)argument; // get target sound level threshold value
		sound_level_threshold = value;
		if (!sound_level_save()) {
			puts("could not save sound level threshold\n");
		}
	}
	printf("sound level threshold set to %u dBa\n", sound_level_threshold);
}

/** set sound level duration
 *  @param[in] argument sound level duration
 */
static void command_sound_level_duration(void* argument)
{
	if (argument) { // tachometer value has been provided
		const uint32_t value = *(uint32_t*)argument; // get target sound level duration value
		sound_level_duration = value;
		if (!sound_level_save()) {
			puts("could not save sound level duration\n");
		}
	}
	printf("sound level duration set to %u s\n", sound_level_duration);
}

/** show/hide received sound level
 *  @param[in] argument not used
 */
static void command_show(void* argument)
{
	(void)argument; // we won't use the argument
	sound_level_show = !sound_level_show; // toggle setting
	puts(sound_level_show ? "show" : "hide");
	puts(" received sound level\n");
}

/** list of all supported commands */
static const struct menu_command_t menu_commands[] = {
	{
		.shortcut = 'h',
		.name = "help",
		.command_description = "display help",
		.argument = MENU_ARGUMENT_NONE,
		.argument_description = NULL,
		.command_handler = &command_help,
	},
	{
		.shortcut = 'v',
		.name = "version",
		.command_description = "show software and hardware version",
		.argument = MENU_ARGUMENT_NONE,
		.argument_description = NULL,
		.command_handler = &command_version,
	},
	{
		.shortcut = 'u',
		.name = "uptime",
		.command_description = "show uptime",
		.argument = MENU_ARGUMENT_NONE,
		.argument_description = NULL,
		.command_handler = &command_uptime,
	},
#if RTC_DATE_TIME
	{
		.shortcut = 'D',
		.name = "date",
		.command_description = "show/set date and time",
		.argument = MENU_ARGUMENT_STRING,
		.argument_description = "[YYYY-MM-DD HH:MM:SS]",
		.command_handler = &command_datetime,
	},
#endif
	{
		.shortcut = 'r',
		.name = "reset",
		.command_description = "reset board",
		.argument = MENU_ARGUMENT_NONE,
		.argument_description = NULL,
		.command_handler = &command_reset,
	},
	{
		.shortcut = 'b',
		.name = "bootloader",
		.command_description = "reboot into DFU bootloader",
		.argument = MENU_ARGUMENT_NONE,
		.argument_description = NULL,
		.command_handler = &command_bootloader,
	},
	{
		.shortcut = 't',
		.name = "threshold",
		.command_description = "get/set sound level threshold (in dBa)",
		.argument = MENU_ARGUMENT_UNSIGNED,
		.argument_description = "[value]",
		.command_handler = &command_sound_level_threshold,
	},
	{
		.shortcut = 'd',
		.name = "duration",
		.command_description = "get/set sound level duration (in seconds)",
		.argument = MENU_ARGUMENT_UNSIGNED,
		.argument_description = "[value]",
		.command_handler = &command_sound_level_duration,
	},
	{
		.shortcut = 's',
		.name = "show",
		.command_description = "show/hide received sound level",
		.argument = MENU_ARGUMENT_NONE,
		.argument_description = NULL,
		.command_handler = &command_show,
	},
};

static void command_help(void* argument)
{
	(void)argument; // we won't use the argument
	printf("available commands:\n");
	menu_print_commands(menu_commands, LENGTH(menu_commands)); // print global commands
}

static void command_version(void* argument)
{
	(void)argument; // we won't use the argument
	printf("firmware date: %04u-%02u-%02u\n", BUILD_YEAR, BUILD_MONTH, BUILD_DAY); // show firmware build date
	// get device identifier (DEV_ID)
	// 0x412: low-density, 16-32 kB flash
	// 0x410: medium-density, 64-128 kB flash
	// 0x414: high-density, 256-512 kB flash
	// 0x430: XL-density, 768-1024 kB flash
	// 0x418: connectivity
	printf("device family: ");
	switch (DBGMCU_IDCODE & DBGMCU_IDCODE_DEV_ID_MASK) {
		case 0: // this is a known issue document in STM32F10xxC/D/E Errata sheet, without workaround
			printf("unreadable\n");
			break;
		case 0x412:
			printf("low-density\n");
			break;
		case 0x410:
			printf("medium-density\n");
			break;
		case 0x414:
			printf("high-density\n");
			break;
		case 0x430:
			printf("XL-density\n");
			break;
		case 0x418:
			printf("connectivity\n");
			break;
		default:
			printf("unknown\n");
			break;
	}
	// show flash size
	printf("flash size: ");
	if (0xffff == DESIG_FLASH_SIZE) {
		printf("unknown (probably a defective micro-controller\n");
	} else {
		printf("%u KB\n", DESIG_FLASH_SIZE);
	}
	// display device identity
	printf("device id: %08x%08x%08x\n", DESIG_UNIQUE_ID0, DESIG_UNIQUE_ID1, DESIG_UNIQUE_ID2);
}

static void command_uptime(void* argument)
{
	(void)argument; // we won't use the argument
	uint32_t uptime = (rtc_get_counter_val() - time_start) / RTC_TICKS_SECOND; // get time from internal RTC
	printf("uptime: %u.%02u:%02u:%02u\n", uptime / (24 * 60 * 60), (uptime / (60 * 60)) % 24, (uptime / 60) % 60, uptime % 60);
}

#if RTC_DATE_TIME
static void command_datetime(void* argument)
{
	char* datetime = (char*)argument; // argument is optional date time
	if (NULL == argument) { // no date and time provided, just show the current day and time
		time_t time_rtc = rtc_get_counter_val() / RTC_TICKS_SECOND; // get time from internal RTC
		struct tm* time_tm = localtime(&time_rtc); // convert time
		printf("date: %d-%02d-%02d %02d:%02d:%02d\n", 1900 + time_tm->tm_year, time_tm->tm_mon, time_tm->tm_mday, time_tm->tm_hour, time_tm->tm_min, time_tm->tm_sec);
	} else { // date and time provided, set it
		const char* malformed = "date and time malformed, expecting YYYY-MM-DD HH:MM:SS\n";
		struct tm time_tm; // to store the parsed date time
		if (strlen(datetime) != (4 + 1 + 2 + 1 + 2) + 1 + (2 + 1 + 2 + 1 + 2)) { // verify date/time is long enough
			printf(malformed);
			return;
		}
		if (!(isdigit((int8_t)datetime[0]) && isdigit((int8_t)datetime[1]) && isdigit((int8_t)datetime[2]) && isdigit((int8_t)datetime[3]) && '-' == datetime[4] && isdigit((int8_t)datetime[5]) && isdigit((int8_t)datetime[6]) && '-' == datetime[7] && isdigit((int8_t)datetime[8]) && isdigit((int8_t)datetime[9]) && ' ' == datetime[10] && isdigit((int8_t)datetime[11]) && isdigit((int8_t)datetime[12]) && ':' == datetime[13] && isdigit((int8_t)datetime[14]) && isdigit((int8_t)datetime[15]) && ':' == datetime[16] && isdigit((int8_t)datetime[17]) && isdigit((int8_t)datetime[18]))) { // verify format (good enough to not fail parsing)
			printf(malformed);
			return;
		}
		time_tm.tm_year = strtol(&datetime[0], NULL, 10) - 1900; // parse year
		time_tm.tm_mon = strtol(&datetime[5], NULL, 10); // parse month
		time_tm.tm_mday = strtol(&datetime[8], NULL, 10); // parse day
		time_tm.tm_hour = strtol(&datetime[11], NULL, 10); // parse hour
		time_tm.tm_min = strtol(&datetime[14], NULL, 10); // parse minutes
		time_tm.tm_sec = strtol(&datetime[17], NULL, 10); // parse seconds
		time_t time_rtc = mktime(&time_tm); // get back seconds
		time_start = time_rtc * RTC_TICKS_SECOND + (rtc_get_counter_val() - time_start); // update uptime with current date
		rtc_set_counter_val(time_rtc * RTC_TICKS_SECOND); // save date/time to internal RTC
		printf("date and time saved: %d-%02d-%02d %02d:%02d:%02d\n", 1900 + time_tm.tm_year, time_tm.tm_mon, time_tm.tm_mday, time_tm.tm_hour, time_tm.tm_min, time_tm.tm_sec);
	}
}
#endif

static void command_reset(void* argument)
{
	(void)argument; // we won't use the argument
	scb_reset_system(); // reset device
	while (true); // wait for the reset to happen
}

static void command_bootloader(void* argument)
{
	(void)argument; // we won't use the argument
	// set DFU magic to specific RAM location
	__dfu_magic[0] = 'D';
	__dfu_magic[1] = 'F';
	__dfu_magic[2] = 'U';
	__dfu_magic[3] = '!';
	scb_reset_system(); // reset system (core and peripherals)
	while (true); // wait for the reset to happen
}

/** process user command
 *  @param[in] str user command string (\0 ended)
 */
static void process_command(char* str)
{
	// ensure actions are available
	if (NULL == menu_commands || 0 == LENGTH(menu_commands)) {
		return;
	}
	// don't handle empty lines
	if (!str || 0 == strlen(str)) {
		return;
	}
	bool command_handled = false;
	if (!command_handled) {
		command_handled = menu_handle_command(str, menu_commands, LENGTH(menu_commands)); // try if this is not a global command
	}
	if (!command_handled) {
		printf("command not recognized. enter help to list commands\n");
	}
}

/** parse and display sound level value
 *  @param[io] str line with dBA measurement
 *  @return parsed measurement (0 if failed)
 *  @warning modifies str
 */
static uint8_t parse_measurement(char* str)
{
	if (strlen(str) < 5) { // minimum size for a valid message
		return 0;
	}
	const char* delimiter = " "; // words are separated by spaces
	const char* value_s = strtok(str, delimiter); // get measurement value
	if (!value_s) {
		return 0;
	}
	const char* unit = strtok(NULL, delimiter); // get measurement unit
	if (!unit) {
		return 0;
	}
	if (strncmp("dBa", unit, 3)) { // the measurement unit is the right one
		return 0;
	}
	const double value_f = atof(value_s); // get measurement value
	if (isnan(value_f) || value_f < 0.1) {
		return 0;
	}
	const uint8_t value_i = round(value_f); // get rounded measurement value
	return value_i;
}

/** program entry point
 *  this is the firmware function started by the micro-controller
 */
void main(void);
void main(void)
{
	rcc_clock_setup_in_hse_8mhz_out_72mhz(); // use 8 MHz high speed external clock to generate 72 MHz internal clock

#if DEBUG
	// enable functionalities for easier debug
	DBGMCU_CR |= DBGMCU_CR_IWDG_STOP; // stop independent watchdog counter when code is halted
	DBGMCU_CR |= DBGMCU_CR_WWDG_STOP; // stop window watchdog counter when code is halted
	DBGMCU_CR |= DBGMCU_CR_STANDBY; // allow debug also in standby mode (keep digital part and clock powered)
	DBGMCU_CR |= DBGMCU_CR_STOP; // allow debug also in stop mode (keep clock powered)
	DBGMCU_CR |= DBGMCU_CR_SLEEP; // allow debug also in sleep mode (keep clock powered)
#else
	// setup watchdog to reset in case we get stuck (i.e. when an error occurred)
	iwdg_set_period_ms(WATCHDOG_PERIOD); // set independent watchdog period
	iwdg_start(); // start independent watchdog
#endif

	board_setup(); // setup board
#if !defined(STLINKV2)
	uart_setup(); // setup USART (for printing)
#endif
	usb_cdcacm_setup(); // setup USB CDC ACM (for printing)
	puts("\nwelcome to the CuVoodoo sound lever enforcer\n"); // print welcome message

#if DEBUG
	// show reset cause
	if (RCC_CSR & (RCC_CSR_LPWRRSTF | RCC_CSR_WWDGRSTF | RCC_CSR_IWDGRSTF | RCC_CSR_SFTRSTF | RCC_CSR_PORRSTF | RCC_CSR_PINRSTF)) {
		puts("reset cause(s):");
		if (RCC_CSR & RCC_CSR_LPWRRSTF) {
			puts(" low-power");
		}
		if (RCC_CSR & RCC_CSR_WWDGRSTF) {
			puts(" window-watchdog");
		}
		if (RCC_CSR & RCC_CSR_IWDGRSTF) {
			puts(" independent-watchdog");
		}
		if (RCC_CSR & RCC_CSR_SFTRSTF) {
			puts(" software");
		}
		if (RCC_CSR & RCC_CSR_PORRSTF) {
			puts(" POR/PDR");
		}
		if (RCC_CSR & RCC_CSR_PINRSTF) {
			puts(" pin");
		}
		putc('\n');
		RCC_CSR |= RCC_CSR_RMVF; // clear reset flags
	}
#endif
#if !(DEBUG)
	// show watchdog information
	printf("setup watchdog: %.2fs", WATCHDOG_PERIOD / 1000.0);
	if (FLASH_OBR & FLASH_OBR_OPTERR) {
		puts(" (option bytes not set in flash: software wachtdog used, not automatically started at reset)\n");
	} else if (FLASH_OBR & FLASH_OBR_WDG_SW) {
		puts(" (software watchdog used, not automatically started at reset)\n");
	} else {
		puts(" (hardware watchdog used, automatically started at reset)\n");
	}
#endif

	// setup RTC
	puts("setup internal RTC: ");
#if defined(BLUE_PILL) || defined(STLINKV2) || defined(BLASTER) // for boards without a Low Speed External oscillator
	// note: the blue pill LSE oscillator is affected when toggling the onboard LED, thus prefer the HSE
	rtc_auto_awake(RCC_HSE, 8000000 / 128 / RTC_TICKS_SECOND - 1); // use High Speed External oscillator (8 MHz / 128) as RTC clock (VBAT can't be used to keep the RTC running)
#else // for boards with an precise Low Speed External oscillator
	rtc_auto_awake(RCC_LSE, 32768 / RTC_TICKS_SECOND - 1); // ensure internal RTC is on, uses the 32.678 kHz LSE, and the prescale is set to our tick speed, else update backup registers accordingly (power off the micro-controller for the change to take effect)
#endif
	rtc_interrupt_enable(RTC_SEC); // enable RTC interrupt on "seconds"
	nvic_enable_irq(NVIC_RTC_IRQ); // allow the RTC to interrupt
	time_start = rtc_get_counter_val(); // get start time from internal RTC
	puts("OK\n");

	puts("setup relay: ");
	gpio_set(GPIO_PORT(RELAY_PIN), GPIO_PIN(RELAY_PIN)); // idle not activated
	gpio_set_mode(GPIO_PORT(RELAY_PIN), GPIO_MODE_OUTPUT_2_MHZ, GPIO_CNF_OUTPUT_OPENDRAIN, GPIO_PIN(RELAY_PIN)); // set pin as output (sink to enable)
	puts("OK\n");

	puts("setup 7-segment display: ");
	led_tm1637_setup();
	led_tm1637_brightness(LED_TM1637_14DIV16); // set maximum brightness
	led_tm1637_time(88, 88); // show test pattern
	led_tm1637_on();
	puts("OK\n");

	puts("setup SPP receiver: ");
	spp_rx_setup();
	puts("OK\n");

	puts("read sound level settings: ");
	flash_internal_eeprom_setup(1); // dedicate one page to store the settings
	if (sound_level_load()) {
		puts("set");
	} else {
		puts("default");
	}
	puts(" values\n");
	command_sound_level_threshold(NULL); // show value
	command_sound_level_duration(NULL); // show value

	// show sound level
	iwdg_reset(); // kick the dog
	led_tm1637_number(sound_level_threshold, false); // display threshold
	sleep_ms(1000); // wait some time for the user to read
	iwdg_reset(); // kick the dog
	led_tm1637_text(" dBa"); // display unit
	sleep_ms(1000); // wait some time for the user to read
	iwdg_reset(); // kick the dog
	led_tm1637_number(sound_level_duration, false); // display duration
	sleep_ms(1000); // wait some time for the user to read
	iwdg_reset(); // kick the dog
	led_tm1637_text(" sec"); // display unit
	sleep_ms(1000); // wait some time for the user to read
	iwdg_reset(); // kick the dog
	led_tm1637_brightness(LED_TM1637_1DIV16); // set minimum brightness
	led_tm1637_number(0, false); // show measurement

	// setup terminal
	terminal_prefix = ""; // set default prefix
	terminal_process = &process_command; // set central function to process commands
	terminal_setup(); // start terminal

	// start main loop
	bool action = false; // if an action has been performed don't go to sleep
	button_flag = false; // reset button flag
	uint32_t sound_level_valid = 0; // last time a valid value has been received
	uint32_t sound_level_under = rtc_get_counter_val(); // last time the threshold has been exceeded
	bool sound_level_invalid = false; // no value has been received for some time
	bool sound_level_exceeded = false; // the level has exceeded the threshold longer than the duration
	while (true) { // infinite loop
		iwdg_reset(); // kick the dog
		if (user_input_available) { // user input is available
			action = true; // action has been performed
			//led_toggle(); // show activity
			char c = user_input_get(); // store receive character
			terminal_send(c); // send received character to terminal
		}
		if (rtc_internal_tick_flag) { // the internal RTC ticked
			rtc_internal_tick_flag = false; // reset flag
			action = true; // action has been performed
			if (0 == (rtc_get_counter_val() % RTC_TICKS_SECOND)) { // one second has passed
				//led_toggle(); // heartbeat
				if (sound_level_exceeded) {
					led_tm1637_brightness(LED_TM1637_14DIV16); // set maximum brightness
					if ((rtc_get_counter_val() / RTC_TICKS_SECOND) % 2) {
						led_tm1637_text("too ");
					} else {
						led_tm1637_text("loud");
					}
				} else if (!sound_level_invalid && (((rtc_get_counter_val() - sound_level_valid) / RTC_TICKS_SECOND) >= 3)) { // no value received
					sound_level_invalid = true; // remember the value is invalid
					led_tm1637_number(0, false); // display empty number
					led_tm1637_brightness(LED_TM1637_1DIV16); // set minimum brightness
				} else if (!sound_level_exceeded && sound_level_valid > sound_level_under && (((rtc_get_counter_val() - sound_level_under) / RTC_TICKS_SECOND) >= sound_level_duration)) { // sound level exceeded for too long
					sound_level_exceeded = true; // remember the value exceeded
					led_on(); // light up reset switch
					gpio_clear(GPIO_PORT(RELAY_PIN), GPIO_PIN(RELAY_PIN)); // enable relay
				}
			}
		}
		if (spp_rx_input_available) {
			action = true; // action has been performed
			//led_toggle(); // show activity
			const char c = spp_rx_input_get(); // get the received data (also clears the flag)
			if (!sound_level_exceeded) {
				if (spp_input_i < LENGTH(spp_input_buffer) - 1) { // only store when there is enough space
					spp_input_buffer[spp_input_i++] = c; // store received data
					spp_input_buffer[spp_input_i] = '\0'; // end string
				}
				if ('\n' == c) { // end of line received
					const uint8_t sound_level = parse_measurement(spp_input_buffer); // parse and display the received measurement
					spp_input_i = 0; // reset buffer for next line
					if (sound_level) {
						sound_level_valid = rtc_get_counter_val(); // remember we got a valid value
						if (sound_level_show) {
							printf("%u dBa\n", sound_level);
						}
						led_tm1637_number(sound_level, false); // display number
						if (sound_level_invalid) {
							sound_level_invalid = false; // remember we got a value
							sound_level_under = sound_level_valid; // remember the value is under the threshold
						}
						if (sound_level < sound_level_threshold) {
							led_tm1637_brightness(LED_TM1637_1DIV16); // set minimum brightness
							sound_level_under = sound_level_valid; // remember the value is under the threshold
						} else {
							led_tm1637_brightness(LED_TM1637_14DIV16); // set maximum brightness
						}
					}
				} // end of line received
			} // !sound_level_exceeded
		} // spp_rx_input_available
		if (action) { // go to sleep if nothing had to be done, else recheck for activity
			action = false;
		} else {
			__WFI(); // go to sleep
		}
	} // main loop
}

/** @brief interrupt service routine called when tick passed on RTC */
void rtc_isr(void)
{
	rtc_clear_flag(RTC_SEC); // clear flag
	rtc_internal_tick_flag = true; // notify to show new time
}