/***************************************************************************
 *   Copyright (C) 09/2007 by Olaf Rempel                                  *
 *   razzor@kopf-tisch.de                                                  *
 *                                                                         *
 *   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; version 2 of the License,               *
 *                                                                         *
 *   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, write to the                         *
 *   Free Software Foundation, Inc.,                                       *
 *   59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.             *
 ***************************************************************************/
#include <avr/io.h>
#include <avr/interrupt.h>

#define F_CPU 8000000
#include <util/delay.h>

#define ADC_REF	PORTA0
#define ADC_U	PORTA1
#define ADC_IM	PORTA2
#define ADC_IP	PORTA3
#define SUMMER	PORTA7

#define LEDRT	PORTB0
#define LEDGN	PORTB1
#define PWM	PORTB2

/* ADC_U vs GND: voltage with prescaler (12V -> 2V; 15mV -> 2.5mV/bit), ref 2.56V */
#define CH_U	((1<<REFS0) | 0x01)

/* ADC_IP vs ADC_IM: current sense (1A -> 100mV; ??mA -> ?mV/bit), gain x20, ref 5V */
#define CH_I	((0<<REFS0) | 0x31)

#define MOD_WAITING	0x00
#define MOD_CHARGING	0x01
#define MOD_READY	0x02

#define VOLTAGE_CONNECT	 9000
#define VOLTAGE_CHARGE	12450
#define CURRENT_CHARGE	17500
#define CURRENT_READY	 2000
#define VOLTAGE_REMOVE	 1000

static uint16_t voltage;
static uint16_t current;

ISR(ADC_vect)
{
	if (ADMUX == CH_I) {
		current = ADCW * 25;
		ADMUX = CH_U;

	} else {
		voltage = ADCW * 15;
		ADMUX = CH_I;
	}
}

ISR(TIM1_OVF_vect)
{
	/* Come back in 1ms */
	TCNT1 = 0xFFFF - 8000;

	/* start ADC again */
	ADCSRA |= (1<<ADSC);

	static uint8_t pwm;
	static uint8_t mode = MOD_WAITING;

	/* charge with constant voltage and current limit */
	if (mode == MOD_CHARGING) {
		if (voltage < (VOLTAGE_CHARGE -25) && current < (CURRENT_CHARGE -500))
			if (pwm < 0xff)
				pwm++;

		if (voltage > VOLTAGE_CHARGE || current > CURRENT_CHARGE)
			if (pwm > 0x00)
				pwm--;

		OCR0A = pwm;
		TCCR0A |= (1<<COM1A1);

	} else {
		pwm = 0;
		TCCR0A &= ~(1<<COM1A1);
	}

	static uint16_t led_timer;
	led_timer = (led_timer +1) & 0x3FF;

	switch (mode) {
	case MOD_WAITING:
		/* green flashing, red off */
		if (led_timer < 0x3F)
			PORTB &= ~(1<<LEDGN);
		else
			PORTB |= (1<<LEDGN) | (1<<LEDRT);

		PORTA |= (1<<SUMMER);

		/* start charging when a voltage > 9V is detected (lipo connected) */
		if (voltage > VOLTAGE_CONNECT)
			mode = MOD_CHARGING;

		break;

	case MOD_CHARGING:
		/* current limit */
		if (voltage < (VOLTAGE_CHARGE -50)) {
			/* green on, red fast blinking */
			if (led_timer & 0x80)
				PORTB &= ~((1<<LEDGN) | (1<<LEDRT));
			else
				PORTB |= (1<<LEDRT);

		/* voltage limit */
		} else {
			/* green on, red slow blinking */
			if (led_timer & 0x200)
				PORTB &= ~((1<<LEDGN) | (1<<LEDRT));
			else
				PORTB |= (1<<LEDRT);
		}

		PORTA |= (1<<SUMMER);

		/* end charging if voltage > 12.45V and current < 200mA */
		if (voltage >= VOLTAGE_CHARGE && current < CURRENT_READY)
			mode = MOD_READY;
		break;

	case MOD_READY:
		/* green on, red flashing */
		if (led_timer < 0x3F)
			PORTB &= ~((1<<LEDGN) | (1<<LEDRT));
		else
			PORTB |= (1<<LEDRT);

		/* beeping */
		if (led_timer < 0x07)
			PORTA &= ~(1<<SUMMER);
		else
			PORTA |= (1<<SUMMER);

		/* wait for lipo disconnect */
		if (voltage < VOLTAGE_REMOVE)
			mode = MOD_WAITING;
		break;
	}
}

int main(void)
{
	/* digital outputs */
	DDRA = (1<<SUMMER);
	DDRB = (1<<LEDGN) | (1<<LEDRT) | (1<<PWM);

	/* analog inputs */
	DIDR0 = (1<<ADC_REF) | (1<<ADC_U) | (1<<ADC_IM) | (1<<ADC_IP);

	/* timer0: running with F_CPU, 8bit Fast PWM (32khz) */
	TCCR0A = (1<<WGM00) | (1<<WGM01);
	TCCR0B = (1<<CS00);

	/* timer1: running with F_CPU */
	TCCR1B = (1<<CS00);

	/* enable iimer1 OVF Interrupt */
	TIMSK1 = (1<<TOIE1);

	/* enable ADC with interrupts, 125kHz clk */
	ADMUX = CH_I;
	ADCSRA = (1<<ADEN) | (1<<ADSC) | (1<<ADIE) | (1<<ADPS2) | (1<<ADPS1);

	sei();

	while (1);
	return 0;
}