led_clock-old/main.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/>.
 *
 */
/** @file main.c
 *  @author King Kévin <kingkevin@cuvoodoo.info>
 *  @date 2016
 *  @brief show the time on a LED strip
 */

/* standard libraries */
#include <stdint.h> // standard integer types
#include <stdio.h> // standard I/O facilities
#include <stdlib.h> // standard utilities
#include <unistd.h> // standard streams
#include <errno.h> // error number utilities
#include <string.h> // string utilities
#include <math.h> // mathematical utilities

/* STM32 (including CM3) libraries */
#include <libopencm3/stm32/rcc.h> // real-time control clock library
#include <libopencm3/stm32/gpio.h> // general purpose input output library
#include <libopencm3/cm3/scb.h> // vector table definition
#include <libopencmsis/core_cm3.h> // Cortex M3 utilities
#include <libopencm3/cm3/nvic.h> // interrupt utilities
#include <libopencm3/stm32/exti.h> // external interrupt utilities
#include <libopencm3/stm32/timer.h> // timer utilities
#include <libopencm3/stm32/adc.h> // ADC utilities
#include <libopencm3/stm32/rtc.h> // real time clock utilities

/* own libraries */
#include "global.h" // board definitions
#include "usart.h" // USART utilities
#include "usb_cdcacm.h" // USB CDC ACM utilities
#include "led_ws2812b.h" // WS2812b LEDs utilities

/** @defgroup main_flags flag set in interrupts to be processed in main task
 *  @{
 */
volatile bool button_flag = false; /**< flag set when board user button has been pressed/released */
volatile bool time_flag = false; /**< flag set when time changed */
volatile bool photoresistor_flag = false; /**< flag set when ambient luminosity is measured */
/** @} */

/** @defgroup main_ticks ticks per time units
 *  @note these are derived from TICKS_PER_SECOND
 *  @note I have to use type variables because defines would be stored in signed integers, leading to an overflow it later calculations
 *  @{
 */
/** the number of ticks in one second (a divisor of 32768 greater than 256*WS2812B_LEDS/60) */
#define TICKS_PER_SECOND 256
/** number of ticks in one second */
const uint32_t ticks_second = TICKS_PER_SECOND;
/** number of ticks in one minute */
const uint32_t ticks_minute = 60*TICKS_PER_SECOND;
/** number of ticks in one hour */
const uint32_t ticks_hour = 60*60*TICKS_PER_SECOND;
/** number of ticks in one midday (12 hours) */
const uint32_t ticks_midday = 12*60*60*TICKS_PER_SECOND;
/** @} */

/** @defgroup battery_adc ADC used to measure battery voltage
 *  @{
 */
#define BATTERY_ADC_CHANNEL ADC_CHANNEL1 /**< ADC channel */
#define BATTERY_PORT GPIOA /**< port on which the battery is connected */
#define BATTERY_PORT_RCC RCC_GPIOA /**< timer port peripheral clock */
#define BATTERY_PIN GPIO1 /**< pin of the port on which the battery is connected */
/** @} */
/** @defgroup photoresistor_adc ADC used to ambient luminosity
 *  @{
 */
#define PHOTORESISTOR_ADC_CHANNEL ADC_CHANNEL0 /**< ADC channel */
#define PHOTORESISTOR_PORT GPIOA /**< port on which the battery is connected */
#define PHOTORESISTOR_PORT_RCC RCC_GPIOA /**< timer port peripheral clock */
#define PHOTORESISTOR_PIN GPIO0 /**< pin of the port on which the battery is connected */
/** @} */


/** RGB values for the WS2812b clock LEDs */
uint8_t clock_leds[WS2812B_LEDS*3] = {0};
/** user input command */
char command[32] = {0};
/** user input command index */
uint8_t command_i = 0;
/** gamma correction lookup table (common for all colors) */
uint8_t gamma_correction_lut[256] = {0};
/** photo-resistor measurement of ambient luminosity */
volatile uint16_t photoresistor_value = 0;
/** photo-resistor voltage for the minimum brightness */
#define PHOTORESISTOR_MIN 2.7
/** photo-resistor voltage for the maximum brightness */
#define PHOTORESISTOR_MAX 1.7
/** factor to dim LED of the clock, depending on the ambient luminosity */
float clock_brightness = 1;
/** minimum LED brightness */
#define BRIGHTNESS_MIN 0.2
/** maximum LED brightness */
#define BRIGHTNESS_MAX 1.0
/** the factor to change the brightness */
#define BRIGHTNESS_FACTOR 0.1

int _write(int file, char *ptr, int len)
{
	int i; // how much data has been sent
	static char newline = 0; // what newline has been sent

	if (file == STDOUT_FILENO || file == STDERR_FILENO) {
		for (i = 0; i < len; i++) {
			if (ptr[i] == '\r' || ptr[i] == '\n') { // send CR+LF newline for any carriage return and line feed combination
				if (newline==0 || (newline==ptr[i])) { // newline has already been detected
					usart_putchar_nonblocking('\r'); // send newline over USART
					usart_putchar_nonblocking('\n'); // send newline over USART
					cdcacm_putchar('\r'); // send newline over USB
					cdcacm_putchar('\n'); // send newline over USB
					newline = ptr[i]; // remember the newline
				}
			} else { // non-newline character
					usart_putchar_nonblocking(ptr[i]); // send byte over USART
				cdcacm_putchar(ptr[i]); // send byte over USB
				newline = 0; // clear new line
			}
		}
		return i;
	}
	errno = EIO;
	return -1;
}

char* b2s(uint32_t binary, uint8_t rjust)
{
	static char string[32+1] = {0}; // the string representation to return
	int16_t bit = LENGTH(string)-1; // the index of the bit to print
	string[bit--] = 0; // terminate string

	while (binary) {
		if (binary & 1) {
			string[bit--] = '1';
		} else {
			string[bit--] = '0';
		}
		binary >>= 1;
	}

	while (32-bit-1<rjust && bit>=0) {
		string[bit--] = '0';
	}

	return &string[bit+1];
}

/** @brief switch off all clock LEDs
 *  @note LEDs need to be set separately
 */
static void clock_clear(void)
{
	// set all colors of all LEDs to 0
	for (uint16_t i=0; i<LENGTH(clock_leds); i++) {
		clock_leds[i] = 0;
	}
}

/** @brief show time on LED clock
 *  @param[in] time in ticks to show
 *  @details show hours and minutes progress as full arcs, show second position as marker. the brightness of the LED shows the progress of the unit. hours are blue, minutes green, seconds red
 *  @note LEDs need to be set separately
 */
static void clock_show_time(uint32_t time)
{
	uint32_t led_hour = (WS2812B_LEDS*(256*(uint64_t)(time%ticks_midday)))/ticks_midday; // scale to LED brightnesses for hours
	uint32_t led_minute = (WS2812B_LEDS*(256*(uint64_t)(time%ticks_hour)))/ticks_hour; // scale to LED brightnesses for minutes
	if (led_hour>=WS2812B_LEDS*256 || led_minute>=WS2812B_LEDS*256) { // a calculation error occurred
		return;
	}
	// show hours and minutes on LEDs
	if (led_hour>led_minute) {
		// show hours in blue (and clear other LEDs)
		for (uint16_t led=0; led<WS2812B_LEDS; led++) {
			clock_leds[led*3+0] = 0;
			clock_leds[led*3+1] = 0;
			if (led_hour>=0xff) { // full hours
				clock_leds[led*3+2] = 0xff;
			} else { // running hours
				clock_leds[led*3+2] = led_hour;
			}
			led_hour -= clock_leds[led*3+2];
		}
		// show minutes in green (override hours)
		for (uint16_t led=0; led<WS2812B_LEDS && led_minute>0; led++) {
			clock_leds[led*3+0] = 0;
			if (led_minute>=0xff) { // full minutes
				clock_leds[led*3+1] = 0xff;
			} else { // running minutes
				clock_leds[led*3+1] = led_minute;
			}
			led_minute -= clock_leds[led*3+1];
			clock_leds[led*3+2] = 0;
		}
	} else {
		// show minutes in green (and clear other LEDs)
		for (uint16_t led=0; led<WS2812B_LEDS; led++) {
			clock_leds[led*3+0] = 0;
			if (led_minute>=0xff) { // full minutes
				clock_leds[led*3+1] = 0xff;
			} else { // running minutes
				clock_leds[led*3+1] = led_minute;
			}
			led_minute -= clock_leds[led*3+1];
			clock_leds[led*3+2] = 0;
		}
		// show hours in blue (override minutes)
		for (uint16_t led=0; led<WS2812B_LEDS && led_hour>0; led++) {
			clock_leds[led*3+0] = 0;
			clock_leds[led*3+1] = 0;
			if (led_hour>=0xff) { // full hours
				clock_leds[led*3+2] = 0xff;
			} else { // running hours
				clock_leds[led*3+2] = led_hour;
			}
			led_hour -= clock_leds[led*3+2];
		}
	}
	// don't show seconds on full minute (better for first time setting, barely visible else)
	if (time%ticks_minute==0) {
		return;
	}
	uint32_t led_second = (WS2812B_LEDS*(256*(uint64_t)(time%ticks_minute)))/ticks_minute; // scale to LED brightnesses for seconds
	uint8_t brightness_second = led_second%256; // get brightness for seconds for last LED
	uint16_t second_led = (WS2812B_LEDS*(time%ticks_minute))/ticks_minute; // get LED for seconds (we only use the last LED as runner instead of all LEDs as arc)
	// set seconds LED
	clock_leds[second_led*3+0] = brightness_second;
	//clock_leds[second_led*3+1] = 0; // clear other colors (minutes/hours indication)
	//clock_leds[second_led*3+2] = 0; // clear other colors (minutes/hours indication)
	// set previous seconds LED
	second_led = ((second_led==0) ? WS2812B_LEDS-1 : second_led-1); // previous LED
	clock_leds[second_led*3+0] = 0xff-brightness_second;
	//clock_leds[second_led*3+1] = 0; // clear other colors (minutes/hours indication)
	//clock_leds[second_led*3+2] = 0; // clear other colors (minutes/hours indication)
}

/** @brief set the LEDs
 *  @details set the LED colors on WS2812b LEDs
 *  @note WS2812b LED color values need to be transmitted separately
 */
static void clock_leds_set(void)
{
	for (uint16_t i=0; i<LENGTH(clock_leds)/3; i++) {
		ws2812b_set_rgb(i,gamma_correction_lut[(uint8_t)(clock_leds[i*3+0]*clock_brightness)],gamma_correction_lut[(uint8_t)(clock_leds[i*3+1]*clock_brightness)],gamma_correction_lut[(uint8_t)(clock_leds[i*3+2]*clock_brightness)]); // set new value (this costs time)
	}
}

/** @brief set the time on the LEDs
 *  @param[in] time time to set
 */
static void clock_set_time(uint32_t time)
{
	clock_show_time(time); // set time
	clock_leds_set(); // set the colors of all LEDs
	ws2812b_transmit(); // transmit set color
}

/** @brief incrementally set the time on the LEDs
 *  @details this will have an animation where time is incremented until it reaches the provided time
 *  @param[in] time time to set
 */
static void clock_animate_time(uint32_t time)
{
	static uint32_t display_time = 0; // the time to display
	while (display_time<time) {
		if (display_time+ticks_hour<=time) { // first set hours
			display_time += ticks_hour; // increment hours
		} else if (display_time+ticks_minute<=time) { // second set minutes
			display_time += ticks_minute; // increment minutes
		} else if (display_time+ticks_second<=time) { // third set seconds
			display_time += ticks_second; // increment seconds
		} else { // finally set time
			display_time = time;
		}
		clock_set_time(display_time); // set time (progress)
		// delay some time for the animation
		for (uint32_t i=0; i<400000; i++) {
			__asm__("nop");
		}
	}
}

/** @brief show animation with fading hours mark on clock LEDs
 */
static void clock_hours(void)
{
	for (uint16_t i=0; i<512; i++) { // fade in and out
		uint8_t brightness = (i>255 ? 512-i-1 : i); // get fade brightness
		for (uint8_t hour=0; hour<12; hour++) { // set all hour colors
			uint16_t led = WS2812B_LEDS/12*hour; // get LED four hour mark
			clock_leds[led*3+0] = brightness; // set brightness
			clock_leds[led*3+1] = brightness; // set brightness
			clock_leds[led*3+2] = brightness; // set brightness
		}
		clock_leds_set(); // set the colors of all LEDs
		ws2812b_transmit(); // transmit set color
		// delay some time for the animation
		for (uint32_t j=0; j<40000; j++) {
			__asm__("nop");
		}
	}
}

/** @brief process user command
 *  @param[in] str user command string (\0 ended)
 */
static void process_command(char* str)
{
	// split command
	const char* delimiter = " ";
	char* word = strtok(str,delimiter);
	if (!word) {
		goto error;
	}
	// parse command
	if (0==strcmp(word,"help")) {
		printf("available commands:\n");
		printf("time [HH:MM:SS]\n");
	} else if (0==strcmp(word,"time")) {
		word = strtok(NULL,delimiter);
		if (!word) {
			printf("%02lu:%02lu:%02lu\n", rtc_get_counter_val()/ticks_hour, (rtc_get_counter_val()%ticks_hour)/ticks_minute, (rtc_get_counter_val()%ticks_minute)/ticks_second);
		} else if (strlen(word)!=8 || word[0]<'0' || word[0]>'2' || word[1]<'0' || word[1]>'9' || word[3]<'0' || word[3]>'5' || word[4]<'0' || word[4]>'9' || word[6]<'0' || word[6]>'5' || word[7]<'0' || word[7]>'9') {
				goto error;
		} else {
			rtc_set_counter_val(((word[0]-'0')*10+(word[1]-'0')*1)*ticks_hour+((word[3]-'0')*10+(word[4]-'0')*1)*ticks_minute+((word[6]-'0')*10+(word[7]-'0')*1)*ticks_second); // set time in RTC counter
			printf("time set\n");
		}	
	} else {
		goto error;
	}

	return; // command successfully processed
error:
	printf("command not recognized. enter help to list commands\n");
}

/** @brief program entry point
 *  this is the firmware function started by the micro-controller
 */
int main(void)
{	
	rcc_clock_setup_in_hse_8mhz_out_72mhz(); // use 8 MHz high speed external clock to generate 72 MHz internal clock
    usart_setup(); // setup USART (for printing)
	cdcacm_setup(); // setup USB CDC ACM (for printing)
    setbuf(stdout, NULL); // set standard out buffer to NULL to immediately print   
    setbuf(stderr, NULL); // set standard error buffer to NULL to immediately print

	// setup LED
	rcc_periph_clock_enable(LED_RCC); // enable clock for LED
	gpio_set_mode(LED_PORT, GPIO_MODE_OUTPUT_2_MHZ, GPIO_CNF_OUTPUT_PUSHPULL, LED_PIN); // set LED pin to 'output push-pull'
	led_off(); // switch off LED to indicate setup started

	// setup button
#if defined(BUTTON_RCC) && defined(BUTTON_PORT) && defined(BUTTON_PIN) && defined(BUTTON_EXTI) && defined(BUTTON_IRQ)
	rcc_periph_clock_enable(BUTTON_RCC); // enable clock for button
	gpio_set_mode(BUTTON_PORT, GPIO_MODE_INPUT, GPIO_CNF_INPUT_PULL_UPDOWN, BUTTON_PIN); // set button pin to input
	gpio_clear(BUTTON_PORT, BUTTON_PIN); // pull down to be able to detect button push (go high)
	rcc_periph_clock_enable(RCC_AFIO); // enable alternate function clock for external interrupt
	exti_select_source(BUTTON_EXTI, BUTTON_PORT); // mask external interrupt of this pin only for this port
	exti_set_trigger(BUTTON_EXTI, EXTI_TRIGGER_RISING); // trigger on both edge
	exti_enable_request(BUTTON_EXTI); // enable external interrupt
	nvic_enable_irq(BUTTON_IRQ); // enable interrupt
#endif

	// setup RTC
	rtc_auto_awake(RCC_LSE, 32768/ticks_second-1); // ensure 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)
	rtc_interrupt_enable(RTC_SEC); // enable RTC interrupt on "seconds"
	nvic_enable_irq(NVIC_RTC_IRQ); // allow the RTC to interrupt

	// generate gamma correction table (with fixed gamma value)
	for (uint16_t i=0; i<LENGTH(gamma_correction_lut); i++) {
		gamma_correction_lut[i] = powf((float)i / (float)LENGTH(gamma_correction_lut), 2.2)*LENGTH(gamma_correction_lut);
	}

	// setup WS2812b LEDs
	ws2812b_setup(); // setup WS2812b LEDs
	clock_clear(); // clear all LEDs
	clock_leds_set(); // set the colors of all LEDs
	ws2812b_transmit(); // transmit set color

	// setup ADC to read battery voltage
	rcc_periph_clock_enable(BATTERY_PORT_RCC); // enable clock for battery GPIO peripheral
	gpio_set_mode(BATTERY_PORT, GPIO_MODE_INPUT, GPIO_CNF_INPUT_ANALOG, BATTERY_PIN); // set battery GPIO as analogue input for the ADC
	rcc_periph_clock_enable(PHOTORESISTOR_PORT_RCC); // enable clock for photo-resistor GPIO peripheral
	gpio_set_mode(PHOTORESISTOR_PORT, GPIO_MODE_INPUT, GPIO_CNF_INPUT_ANALOG, PHOTORESISTOR_PIN); // set photo-resistor GPIO as analogue input for the ADC
	rcc_periph_clock_enable(RCC_ADC1); // enable clock for ADC peripheral
	adc_off(ADC1); // switch off ADC while configuring it
	// configuration is correct per default
	adc_set_single_conversion_mode(ADC1); // we just want one measurement
	adc_set_sample_time_on_all_channels(ADC1, ADC_SMPR_SMP_28DOT5CYC); // use 28.5 cycles to sample (long enough to be stable)
	adc_enable_temperature_sensor(ADC1); // enable internal voltage reference
	adc_enable_discontinuous_mode_regular(ADC1, 1); // do only one conversion per sequence
	adc_enable_external_trigger_regular(ADC1, ADC_CR2_EXTSEL_SWSTART); // use software trigger to start conversion
	adc_power_on(ADC1); // switch on ADC
	for (uint32_t i=0; i<800000; i++) { // wait t_stab for the ADC to stabilize
		__asm__("nop");
	}
	adc_reset_calibration(ADC1); // remove previous non-calibration
	adc_calibration(ADC1); // calibrate ADC for less accuracy errors

	printf("welcome to the CuVoodoo LED clock\n"); // print welcome message
	led_on(); // switch on LED to indicate setup completed

	// read internal reference 1.2V and RTC battery voltages
	uint8_t channels[] = {ADC_CHANNEL17, BATTERY_ADC_CHANNEL}; // voltages to convert
	adc_set_regular_sequence(ADC1, LENGTH(channels), channels); // set channels to convert
	adc_start_conversion_regular(ADC1); // start conversion to get first voltage of this group
	while (!adc_eoc(ADC1)); // wait until conversion finished
	uint16_t ref_value = adc_read_regular(ADC1); // read internal reference 1.2V voltage value
	adc_start_conversion_regular(ADC1); // start conversion to get second voltage of this group
	while (!adc_eoc(ADC1)); // wait until conversion finished
	uint16_t battery_value = adc_read_regular(ADC1); // read converted battery voltage
	float battery_voltage = battery_value*1.2/ref_value; // calculate battery voltage
	if (battery_voltage<1.0) {
		printf("no battery detected\n");
	} else {
		if (battery_voltage<2.4) { // low battery voltage
			printf("/!\\ low ");
			for (uint16_t led=0; led<2; led++) { // display red on 2 LEDs
				clock_leds[led*3+0] = 0xff; // set red
			}
		} else if (battery_voltage>3.0) { // battery full
			for (uint16_t led=0; led<WS2812B_LEDS; led++) { // display green on all LEDs
				clock_leds[led*3+1] = 0xff; // set green
			}
		} else { // intermediate batter voltage
			for (uint16_t led=0; led<(uint8_t)(WS2812B_LEDS*(battery_voltage-2.4)/0.6); led++) { // display blue on proportional LEDs
				clock_leds[led*3+2] = 0xff; // set blue
			}
		}
		printf("battery voltage: %.2fV\n", battery_voltage);
		clock_leds_set(); // set the colors of all LEDs
		ws2812b_transmit(); // transmit set color
		for (uint32_t i=0; i<10000000; i++) { // display for a small while
			__asm__("nop");
		}	
	}
	
	// now use interrupts to only measure ambient luminosity
	channels[0] = PHOTORESISTOR_ADC_CHANNEL; // only measure ambient luminosity
	adc_set_regular_sequence(ADC1, 1, channels); // set now group
	adc_enable_eoc_interrupt(ADC1); // enable interrupt for end of convertion
	nvic_enable_irq(NVIC_ADC1_2_IRQ); // enable ADC interrupts

	// get date and time
	printf("current time: %02lu:%02lu:%02lu\n", rtc_get_counter_val()/ticks_hour, (rtc_get_counter_val()%ticks_hour)/ticks_minute, (rtc_get_counter_val()%ticks_minute)/ticks_second); // display time
	clock_animate_time(rtc_get_counter_val()); // set time with animation

	printf("input commands\n");
	bool action = false; // if an action has been performed don't go to sleep
	button_flag = false; // reset button flag
	char c = ' '; // to store received character
	bool char_flag = false; // a new character has been received
	while (true) { // infinite loop
		while (usart_received) { // data received over UART
			action = true; // action has been performed
			led_toggle(); // toggle LED
			c = usart_getchar(); // store receive character
			char_flag = true; // notify character has been received
		}
		while (cdcacm_received) { // data received over USB
			action = true; // action has been performed
			led_toggle(); // toggle LED
			c = cdcacm_getchar(); // store receive character
			char_flag = true; // notify character has been received
		}
		while (char_flag) { // user data received
			char_flag = false; // reset flag
			action = true; // action has been performed
			printf("%c",c); // echo receive character
			if (c=='\r' || c=='\n') { // end of command received
				if (command_i>0) { // there is a command to process
					command[command_i] = 0; // end string
					command_i = 0; // prepare for next command
					process_command(command); // process user command
				}
			} else { // user command input
				command[command_i] = c; // save command input
				if (command_i<LENGTH(command)-2) { // verify if there is place to save next character
					command_i++; // save next character
				}
			}
		}
		while (button_flag) { // user pressed button
			action = true; // action has been performed
			printf("time incremented by 1 second\n");
			rtc_set_counter_val(rtc_get_counter_val()+ticks_second); // increment time
			//led_toggle(); // toggle LED
			for (uint32_t i=0; i<1000000; i++) { // wait a bit to remove noise and double trigger
				__asm__("nop");
			}
			button_flag = false; // reset flag
		}
		while (time_flag) { // time passed
			time_flag = false; // reset flag
			action = true; // action has been performed
			if ((rtc_get_counter_val()%(ticks_second/10))==0) { // one tenth of a second passed
				adc_start_conversion_regular(ADC1); // start measuring ambient luminosity
			}
			if ((rtc_get_counter_val()%ticks_second)==0) { // one second passed
				//led_toggle(); // don't use the LED, this confuses the 32.768 kHz oscillator
			}
			if ((rtc_get_counter_val()%ticks_minute)==0) { // one minute passed
				printf("%02lu:%02lu:%02lu\n", rtc_get_counter_val()/ticks_hour, (rtc_get_counter_val()%ticks_hour)/ticks_minute, (rtc_get_counter_val()%ticks_minute)/ticks_second); // display time
			}
			if ((rtc_get_counter_val()%ticks_hour)==0) { // one hours passed
				clock_hours(); // show hour markers
			}
			if (rtc_get_counter_val()>=ticks_midday*2) { // one day passed
				rtc_set_counter_val(rtc_get_counter_val()%ticks_midday); // reset time counter
            }
			clock_set_time(rtc_get_counter_val()); // set time
		}
		while (photoresistor_flag) { // new photo-resistor value has been measured
			photoresistor_flag = false; // reset flag
			action = true; // action has been performed
			float photoresistor_voltage = photoresistor_value*1.2/ref_value; // calculate voltage from value
			float new_clock_brightness = 0; // to calculate new brightness
			if (photoresistor_voltage<PHOTORESISTOR_MAX) { // high ambient luminosity
				new_clock_brightness = BRIGHTNESS_MAX; // set highest brightness
			} else if (photoresistor_voltage>PHOTORESISTOR_MIN) { // low ambient luminosity
				new_clock_brightness = BRIGHTNESS_MIN; // set low brightness
			} else { // intermediate ambient luminosity
				new_clock_brightness = BRIGHTNESS_MIN+(BRIGHTNESS_MAX-BRIGHTNESS_MIN)*(1-(photoresistor_voltage-PHOTORESISTOR_MAX)/(PHOTORESISTOR_MIN-PHOTORESISTOR_MAX)); // set variable brightness
			}
			clock_brightness = clock_brightness*(1-BRIGHTNESS_FACTOR)+new_clock_brightness*BRIGHTNESS_FACTOR; // calculate new brightness based on factor
			//printf("photo-resistor voltage: %f, clock brightness: %f\n", photoresistor_voltage, clock_brightness);
		}
		if (action) { // go to sleep if nothing had to be done, else recheck for activity
			action = false;
		} else {
			__WFI(); // go to sleep
		}
	}

	return 0;
}

#if defined(BUTTON_ISR) && defined(BUTTON_EXTI)
/** @brief interrupt service routine called when button is pressed of released */
void BUTTON_ISR(void)
{
	exti_reset_request(BUTTON_EXTI); // reset interrupt
	button_flag = true; // perform button action
}
#endif

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

/** @brief interrupt service routine called when ADC conversion completed */
void adc1_2_isr(void)
{
	photoresistor_value = adc_read_regular(ADC1); // read measured photo-resistor value (clears interrupt flag)
	photoresistor_flag = true; // notify new ambient luminosity has been measured
}