/***************************************************************************
 *   Copyright (C) 04/2011 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>
#include <avr/eeprom.h>
#include <avr/sleep.h>

/*
 * attiny24: (no self programming, 2.7V BOD, 8MHz internal RC Osz)
 * LFUSE = 0xC2
 * HFUSE = 0xDD
 * EFUSE = 0xFF
 *
 * RC5 Input on PB2 (INT0)
 * PROGMODE Jumper (active low) on PB1
 * OUTPUT (active low) on PB0
 */

/* RC5 bitlength is 1778us +/-10% convert to timer0 ticks (8us) */
#define BITWIDTH                (1778 / 8)
#define BITWIDTH_MIN            (BITWIDTH - (BITWIDTH / 10))
#define BITWIDTH_MAX            (BITWIDTH + (BITWIDTH / 10))

#define RC5_BITCNT              14
#define RC5_CMD_MASK            0x37FF
#define RC5_COMPLETE            0x8000

#define PROGMODE_CHECK()        (!(PINB & (1<<PINB1)))
#define OUTPUT_ON()             { PORTB &= ~(1<<PORTB0); }
#define OUTPUT_OFF()            { PORTB |= (1<<PORTB0); }

struct ee_param {
        uint16_t rc5cmd;
        uint8_t state;
};

struct ee_param params;
struct ee_param params_in_eeprom EEMEM = {
        .rc5cmd = 0x350C,
        .state = 0x00,
};

static uint8_t bitcnt;
static volatile uint16_t value;

ISR(EXT_INT0_vect)
{
        if (bitcnt == 0)
                value = 0;

        bitcnt++;

        value = (value << 1);
        if (!(PINB & (1<<PINB2)))
                value |= 0x0001;

        /* setup sample window for next edge */
        OCR0A = TCNT0 + BITWIDTH_MIN;
        OCR0B = TCNT0 + BITWIDTH_MAX;

        /* clear and enable COMPA / COMPB */
        TIFR0 = (1<<OCF0A) | (1<<OCF0B);
        TIMSK0 |= (1<<OCIE0A) | (1<<OCIE0B);

        /* disable INT0 until COMPA hits */
        GIMSK &= ~(1<<INT0);
}

ISR(TIM0_COMPA_vect)
{
        /* clear and enable INT0 */
        GIFR = (1<<INTF0);
        GIMSK |= (1<<INT0);
}

ISR(TIM0_COMPB_vect)
{
        /* disable sample window */
        TIMSK0 &= ~((1<<OCIE0A) | (1<<OCIE0B));

        /* final bit received? */
        if (bitcnt >= RC5_BITCNT)
                value |= RC5_COMPLETE;

        bitcnt = 0;
}

int main(int argc, char *argv[])
{
        DDRB = (1<<PORTB0);

        /* pullup on RC5IN and PROGMEM, OUTPUT is low active */
        PORTB = (1<<PORTB2) | (1<<PORTB1) | (1<<PORTB0);

        /* INT0: both edges generate interrupt */
        MCUCR = (1<<ISC00);
        GIMSK = (1<<INT0);

        /* Timer0: 8Mhz/64 */
        TCCR0B = (1<<CS01) | (1<<CS00);

        /* load configuration, restore state */
        eeprom_read_block(&params, &params_in_eeprom, sizeof(struct ee_param));
        if (params.state) {
                OUTPUT_ON();
        } else {
                OUTPUT_OFF();
        }

        /* all interrupts can wake up */
        set_sleep_mode(SLEEP_MODE_IDLE);
        sei();

        uint16_t old_value = 0x0000;

        while (1) {
                /* wait for next interrupt */
                sleep_mode();

                if (value & RC5_COMPLETE) {
                        /* PROGMODE jumper set? */
                        if (PROGMODE_CHECK()) {
                                params.rc5cmd = (value & RC5_CMD_MASK);
                                eeprom_write_block(&params, &params_in_eeprom, sizeof(struct ee_param));

                        /* current command matches stored one */
                        } else if (params.rc5cmd == (value & RC5_CMD_MASK) && value != old_value) {
                                if (params.state) {
                                        params.state = 0;
                                        OUTPUT_OFF();
                                } else {
                                        params.state = 1;
                                        OUTPUT_ON();
                                }

                                eeprom_write_block(&params, &params_in_eeprom, sizeof(struct ee_param));
                                old_value = value;
                        }

                        value = 0x0000;
                }
        }

        return 0;
}