/*
 * OVERVIEW
 *
 * Powering up:
 * Immediately after reset, we power down the entire system.
 * We wake up only after the button is pressed for a sufficiently long time.
 *
 * Heater output:
 * The heater output is driven by Timer/Counter 1 in PWM mode.
 * We want to be able to measure the battery voltage both when the
 * output is on, and when the output is off. So we set the T/C1 clock
 * prescaler so that the T/C1 is slow enough, we enable the T/C1 interrupts
 * both on compare match and on overflow. After the interrupt, we trigger
 * the battery voltage measurement with ADC.
 *
 * ADC:
 * To avoid transients, we measure each battery state (when the heater is on
 * and when it is off) separately, and we drop the first few readings.
 * We calculate a running average of the readings to achieve higher accuracy.
 *
 * Buttons:
 * There are two buttons (+ and -). Any button can wake the system up from
 * the power-down state.
 * TODO: When the system is woken up by the "-" button,
 * it starts with the minimum output power, when it is woken up by the "+"
 * button, it start with the maximum output power.
 * When running, the "-" button is used for decreasing the output power,
 * the "+" button is for increasing it.
 * When on the lowest power state, the "-" button switches the system off.
 * Long "-" button press switches the system off, long "+" button
 * press sets the output power to maximum.
 *
 * Status LED:
 * When powering up by a button press, the LED goes on to provide a visual
 * feedback, and is switched off after the button is released.
 * After a button press, the # of blinks of the LED reflects the
 * chosen output power level for some time. Afterwards, it displays
 * the battery level.
 * When the battery is completely exhausted, the output power is switched
 * off, the LED keeps blinking for some time, and then the whole system is
 * switched off to avoid deep discharge of the battery.
 *
 * Timing:
 * The firmware is timed by the Watchdog Timer interrupt. Most of the
 * processing is done from the main loop, IRQs only set various flags
 * or trigger other events.
 */

#include <avr/interrupt.h>
#include <avr/io.h>
#include <avr/power.h>
#include <avr/sleep.h>
#include <avr/wdt.h>
#include <util/delay.h>

#include "logging.h"

/* waking up from the power down state by a button press */
#define WAKEUP_POLL 50	// msec
#define WAKEUP_LIMIT 5	// times WAKEUP_POLL

/* which state (output on or output off) are we measuring now */
static volatile unsigned char adc_type, adc_drop;
#define ADC_RUNAVG_SHIFT 5	// running average shift on batt_on, batt_off
static volatile uint16_t batt_on, batt_off; // measured voltage

/*
 * The voltage divider has 1M5 and 300K resistors (i.e. it measures 1/6th of
 * the real voltage), ADC uses 1.1V internal reference.
 * Macro to calculate upper eight bits of the ADC running-averaged value
 * from the voltage in milivolts.
 */
#define ADC_1100MV_VALUE	1071	// measured, not exactly 1100
#define MV_TO_ADC8(mV)	((unsigned char)(((uint32_t)(1UL << ADC_RUNAVG_SHIFT) \
				* (1024UL * (mV)) \
				/ (6UL * ADC_1100MV_VALUE)) >> 8))
static unsigned char batt_levels[] = {
	MV_TO_ADC8(3350),
	MV_TO_ADC8(3700),
	MV_TO_ADC8(3900),
};
#define BATT_N_LEVELS 	(sizeof(batt_levels) / sizeof(batt_levels[0]))

/* output power and PWM calculation */
#define PWM_TOP	255
#define PWM_MAX	(PWM_TOP - 8)	// to allow for ADC "batt_off" measurements

/*
 * The values in power_levels[] array are voltages at which the load
 * would give the expected power (we don't have sqrt() function,
 * so we cannot use mW values directly. They can be calculated as
 * voltage[V] = sqrt(load_resistance[Ohm] * expected_power[W])
 * or
 * voltage[mV] = sqrt(load_resistance[mOhm] * expected_power[mW])
 *
 * I use 1.25 W as minimum power, each step is sqrt(2)*previous_step,
 * so the 5th step is 5 W.
 */
static unsigned char power_levels[] = {
	MV_TO_ADC8(1581),	// 1250 mW for 2 Ohm load
	MV_TO_ADC8(1880),	// 1768 mW for 2 Ohm load
	MV_TO_ADC8(2236),	// 2500 mW for 2 Ohm load
	MV_TO_ADC8(2659),	// 3536 mW for 2 Ohm load
	MV_TO_ADC8(3162),	// 5000 mW for 2 Ohm load
};
#define N_POWER_LEVELS	(sizeof(power_levels) / sizeof(power_levels[0]))

static unsigned char power_level = 0; // selected power level
static unsigned char power_level_changed; // for visual feedback

#define LED_PWRCHANGE_COUNT	3
#define LED_BATTEMPTY_COUNT	60

/* timing by WDT */
static volatile unsigned char jiffies, next_clock_tick;

/* button press duration (in jiffies) */
#define BUTTON_SHORT_MIN	1
#define BUTTON_LONG_MIN		10


/* ========= Analog to Digital Converter (battery voltage) ========== */
static void adc_init()
{
	power_adc_enable();

	ADCSRA = _BV(ADEN)			// enable
		| _BV(ADPS1) | _BV(ADPS0)	// clk/8 = 125 kHz
		| _BV(ADIE);			// enable IRQ
	ADMUX = _BV(REFS1) | _BV(MUX1) | _BV(MUX0);
		// 1.1V reference, PB3 pin, single-ended
	DIDR0 |= _BV(ADC3D);	// PB3 pin as analog input
}

static void adc_susp()
{
	ADCSRA &= ~_BV(ADEN);	// disable ADC
	DIDR0 &= ~_BV(ADC3D);	// disable analog input on PB3

	power_adc_disable();
}

static void adc_start_measurement()
{
	ADCSRA |= _BV(ADSC);
}

ISR(ADC_vect)
{
	uint16_t adcw = ADCW;

	if (adc_drop) {
		adc_drop--;
		ADCSRA |= _BV(ADSC);
		return;
	}

	// TODO: We may want to disable ADC after here to save power,
	// but compared to the heater power it would be negligible,
	// so don't bother with it.
	if (adc_type == 0) {
		if (batt_off) {
			batt_off += adcw - (batt_off >> ADC_RUNAVG_SHIFT);
		} else {
			batt_off = adcw << ADC_RUNAVG_SHIFT;
		}
	} else {
		if (batt_on) {
			batt_on += adcw - (batt_on >> ADC_RUNAVG_SHIFT);
		} else {
			batt_on = adcw << ADC_RUNAVG_SHIFT;
		}
	}
}

/* ===================== Timer/Counter1 for PWM ===================== */
static void pwm_init()
{
	power_timer1_enable();

	DDRB |= _BV(PB4);
	PORTB &= ~_BV(PB4);

	// TCCR1 = _BV(CS10); // clk/1 = 1 MHz
	TCCR1 = _BV(CS11) | _BV(CS13); // clk/512 = 2 kHz
	GTCCR = _BV(COM1B1) | _BV(PWM1B);
	OCR1C = PWM_TOP;
	// OCR1B = steps[0];
	OCR1B = 0;
	TIMSK = _BV(OCIE1B) | _BV(TOIE1);
}

static void pwm_susp()
{
	TCCR1 = 0;
	TIMSK = 0;
	GTCCR = 0;
	PORTB &= ~_BV(PB4);
}

ISR(TIM1_OVF_vect)
{
	adc_drop = 2;
	adc_type = 1;
	adc_start_measurement();
}

ISR(TIM1_COMPB_vect)
{
	adc_drop = 2;
	adc_type = 0;
	adc_start_measurement();
}

static void pwm_set(unsigned char pwm)
{
	OCR1B = pwm;
}

/* ===================== Status LED on pin PB2 ======================= */
static void status_led_init()
{
	DDRB |= _BV(PB2);
	PORTB &= ~_BV(PB2);
}

static void status_led_on()
{
	PORTB |= _BV(PB2);
}

static void status_led_off()
{
	PORTB &= ~_BV(PB2);
}

static unsigned char status_led_is_on()
{
	return PORTB & _BV(PB2) ? 1 : 0;
}

/* ================== Buttons on pin PB0 and PB1 ===================== */
static void buttons_init()
{
	DDRB &= ~(_BV(PB0) | _BV(PB1)); // set as input
	PORTB |= _BV(PB0) | _BV(PB1);	// internal pull-up

        GIMSK &= ~_BV(PCIE); // disable pin-change IRQs
        PCMSK = 0; // disable pin-change IRQs on all pins of port B
}

static void buttons_susp()
{
	buttons_init();

	GIMSK |= _BV(PCIE);
	PCMSK |= _BV(PCINT0) | _BV(PCINT1);
}

static unsigned char buttons_pressed()
{
	return (
		(PINB & _BV(PB0) ? 0 : 1)
		|
		(PINB & _BV(PB1) ? 0 : 2)
	);
}

static unsigned char buttons_wait_for_release()
{
	uint16_t wake_count = 0;

	do {
		if (++wake_count > WAKEUP_LIMIT)
			status_led_on(); // inform the user

		_delay_ms(WAKEUP_POLL);
	} while (buttons_pressed());

	status_led_off();

	return wake_count > WAKEUP_LIMIT;
}

ISR(PCINT0_vect)
{
        // empty - let it wake us from sleep, but do nothing else
}

/* ==== Watchdog Timer for timing blinks and other periodic tasks ==== */
static void wdt_init()
{
	next_clock_tick = 0;
	jiffies = 0;
	WDTCR = _BV(WDIE) | _BV(WDP1); // interrupt mode, 64 ms
}

static void wdt_susp()
{
	wdt_disable();
}

ISR(WDT_vect) {
	next_clock_tick = 1;
	jiffies++;
}

/* ====== Hardware init, teardown, powering down and waking up ====== */
static void hw_setup()
{
	power_all_disable();

	pwm_init();
	adc_init();
	status_led_init();
	wdt_init();
}

static void hw_suspend()
{
	adc_susp();
	pwm_susp();
	status_led_init(); // we don't have a separate _susp() here
	buttons_susp();
	wdt_susp();

	power_all_disable();
}

static void power_down()
{
	hw_suspend();

	do {
		// G'night
		set_sleep_mode(SLEEP_MODE_PWR_DOWN);
		sleep_enable();
		sleep_bod_disable();
		sei();
		sleep_cpu();

		// G'morning
		cli();
		sleep_disable();

		// allow wakeup by long button-press only
	} while (!buttons_wait_for_release());

	// OK, wake up now
	hw_setup();
}

/* ============ Status LED blinking =================================== */
static unsigned char blink_on_time, blink_off_time, n_blinks;
static unsigned char blink_counter;

static unsigned char battery_level()
{
	unsigned char i, adc8;

	// NOTE: we use 8-bit value only, so we don't need lock to protect
	// us against concurrently running ADC IRQ handler:
	adc8 = batt_off >> 8;

	for (i = 0; i < BATT_N_LEVELS; i++)
		if (batt_levels[i] > adc8)
			break;

	return i;
}

static void status_led_next_pattern()
{
	static unsigned char battery_exhausted;

	if (power_level_changed) {
		power_level_changed--;
		n_blinks = power_level + 1;
	} else {
		unsigned char b_level = battery_level();
		if (b_level) {
			battery_exhausted = 0;
		} else if (battery_exhausted) {
			if (!--battery_exhausted)
				power_down();
		} else {
			battery_exhausted = LED_BATTEMPTY_COUNT;
		}

		n_blinks = b_level + 1;
	}

	blink_on_time = 2;
	blink_off_time = 1;
	blink_counter = 10;
}

static void timer_blink()
{
	if (blink_counter) {
		blink_counter--;
	} else if (!status_led_is_on()) {
		status_led_on();
		blink_counter = blink_on_time;
	} else if (n_blinks) {
		--n_blinks;
		status_led_off();
		blink_counter = blink_off_time;
	} else {
		status_led_next_pattern();
	}
}

/* ======== Button press detection and  handling ===================== */
static void button_pressed(unsigned char button, unsigned char long_press)
{
	// ignore simlultaneous button 1 and 2 press
	// Note: we set power_level_changed after each button press,
	// even when the power is at maximum, to provide visual feedback
	// with status LED.
	if (long_press) {
		if (button == 1) {
			power_down();
			return;
		} else if (button == 2) {
			power_level = N_POWER_LEVELS-1;
		}
	} else { // short press
		if (button == 1) {
			if (power_level > 0) {
				--power_level;
			} else {
				power_down();
				return;
			}
		} else if (button == 2) {
			if (power_level < N_POWER_LEVELS-1) {
				++power_level;
			}
		}
	}
	power_level_changed = LED_PWRCHANGE_COUNT;
	status_led_next_pattern();
}

static unsigned char button_state, button_state_time;

static void timer_check_buttons()
{
	unsigned char newstate = buttons_pressed();

	if (newstate == button_state) {
		if (newstate && button_state_time < BUTTON_LONG_MIN)
			++button_state_time;

		if (newstate && button_state_time >= BUTTON_LONG_MIN) {
			status_led_on();
		}
		return;
	}

	if (newstate) {
		button_state = newstate;
		button_state_time = 0;
		return;
	}

	// just released
	if (button_state_time >= BUTTON_SHORT_MIN)
		button_pressed(button_state,
			button_state_time >= BUTTON_LONG_MIN ? 1 : 0);

	button_state = newstate;
	button_state_time = 0;
}

/* ===================== Output power control ======================== */
static void calculate_power_level()
{
	uint32_t pwm;
	unsigned char batt_on8;

	if (battery_level() == 0 || batt_on == 0) {
		pwm_set(0);
		// TODO power_down() after some time
		return;
	}

	batt_on8 = batt_on >> 8;

	pwm = (uint32_t)PWM_TOP * power_levels[power_level]
		* power_levels[power_level];
	pwm /= (uint32_t)batt_on8 * batt_on8;

	if (pwm > PWM_MAX)
		pwm = PWM_MAX;

	log_byte(0x10 + power_level);
	log_byte(batt_on8);
	log_byte(pwm & 0xFF);

	pwm_set(pwm);
}

int main()
{
	log_init();

#if 0
	log_word(batt_levels[0]);
	log_word(batt_levels[1]);
	log_word(batt_levels[2]);
	log_flush();
#endif
	log_byte(power_levels[0]);
	log_byte(power_levels[4]);
	log_flush();

	power_down();

	sei();

	// we try to be completely IRQ-driven, so just wait for IRQs here
	while(1) {
		cli();
		set_sleep_mode(SLEEP_MODE_IDLE);
		sleep_enable();
		// keep BOD active, no sleep_bod_disable();
		sei();
		sleep_cpu();
		sleep_disable();

		// FIXME: Maybe handle new ADC readings as well?
		if (next_clock_tick) {
			next_clock_tick = 0;
			timer_blink();
			// this has to be after the timer_blink() call
			// to override the status LED during long button press
			timer_check_buttons();

			if ((jiffies & 0x0F) == 0) {
				calculate_power_level();
#if 0
				log_byte(0xcc);
				log_byte(i);
				log_byte(batt_off >> 8);
				log_byte(batt_on >> 8);
#endif
			}
			log_flush();
		}
	}
}