/**
 * Simple lego power function remote control
 *
 * Inspired by the work of Sivan Toledo
 *  http://www.tau.ac.il/~stoledo/lego/AVR-ir/
 *  
 *  2007, Pat Hanrahan, hanrahan@cs.stanford.edu
 *
 */

#include <avr/io.h>
#include <avr/delay.h>

/*
 attiny13 pinout for remote control

               +--------------+
         reset |  1 pb5 vcc 8 |
          back |  2 pb3 pb2 7 | forw
         right |  3 pb4 pb1 6 | left
               |  4 gnd pb0 5 | oc0a -> irled
               +--------------+
*/

#define PININ (_BV(1)|_BV(2)|_BV(3)|_BV(4))
#define LEFT  _BV(1)
#define FORW  _BV(2)
#define BACK  _BV(3)
#define RIGHT _BV(4)

/*
 *
 */
void setup(void)
{
    // PB0 is outout
    DDRB = _BV(0);	
    // Pull-up input pins
    PORTB = PININ;
 
    // 9600000/8 Hz / (2 * 16) = 37500 Hz
    OCR0A = 16;

    // toggle output compare A (=PB0)
    TCCR0A = (1 << COM0A0)|(1<<WGM01);
}

void on(void)
{
    // start timer; divide by 8
    TCCR0B = (1 << CS01);
}

void off(void)
{
    // stop timer
    TCCR0B = 0;

    // clear PB0
    PORTB = PININ;
}

void xmit( uint16_t ontime, uint16_t offtime ) {  
    on();
    _delay_loop_2(ontime); // 4 * ontime clocks
    off();
    _delay_loop_2(offtime);
}

/*
 * Computed these from the numbers on Sivan's web site
 *
 *  counts * 64 * 9600000/14745000
 *
 * He measured the intervals using a 14745600 crystal
 * divided by 64. We are running at 9600000.
 *
 * signal    60
 * start    215
 * lo        40
 * hi        60
 * end    15000
 *
 * Finally, divide by 4 so we can call _delay_loop_2
 * which executes 4 cycles per value.
 */
#define ONTIME  (2500/4)
#define HITIME  (4583/4)
#define LOTIME  (1666/4)
#define BTIME   (9200/4)
#define ETIME   (625000/4)

void xmitcode(uint16_t code) {
    xmit(ONTIME,BTIME);

    for( int i = 0; i < 16; i++ ) {
       xmit(ONTIME, (code & 0x8000) ? HITIME : LOTIME );
       code = code << 1;
    }

    xmit(ONTIME,0);
    // calling _delay_loop_2 with ETIME causes an overflow
    for( int i = 0; i < 256; i++ )
       _delay_loop_2(ETIME/256);
}



#define CH1RFORBFOR 0x015b
#define CH1RFORBREV 0x0197
#define CH1RREVBFOR 0x0168
#define CH1RREVBREV 0x01a4

#define CH1RFOR   0x8117
#define CH1RREV   0x8124
#define CH1BFOR   0x8142
#define CH1BREV   0x818e

#define CH1NONE   0x010e

/*
 *
 */
int main(void)
{
    setup();

    for(;;) {
        uint8_t pin = ~(PINB & PININ);

	if( pin & FORW )
	    xmitcode(CH1RFORBREV);
	else if( pin & BACK )
	    xmitcode(CH1RREVBFOR);
	else if( pin & LEFT )
	    xmitcode(CH1RREVBREV);
	else if( pin & RIGHT )
	    xmitcode(CH1RFORBFOR);
	else
	    xmitcode(CH1NONE);
    }
}