/************************************************************************/
/*                                                                      */
/*                      Key + LED over the same wire (4 times)          */
/*                                                                      */
/*              Author: P. Dannegger                                    */
/*            CoAuthor: F. Brunner                                      */
/*                                                                      */
/************************************************************************/

#define F_CPU 1000000L

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

uint8_t key_state;                      // debounced key state:
                                        // bit = 1: key pressed
uint8_t key_press;                      // key press detect

void wait7(void) {                      // short delay to settle ADC MUX
    _delay_us(0.5);
}

static uint8_t scan_tast( void )
{
  uint8_t saveport = PORTB;
  uint8_t keys=0;

  PORTB = 0xFF;                         // weak pull ups on
  DDRB = 0;

  ACSR = 1<<ACBG;                       // compare with 1.1V
  ADCSRA = 0;                           // disable ADC
  ADCSRB = 0;                           // select AIN0 (PB1)

  _delay_us(10);                        // time to pull up released keys

  if( ACSR & 1<<ACO )                   // read comparator output
    keys |= 1<<1;

  ADCSRB = 1<<ACME;
  ADMUX = 1<<MUX0;                      // select ADC1 (PB2)
  wait7();                              // time to compare
  if( ACSR & 1<<ACO )
    keys |= 1<<2;

  ADMUX = 1<<MUX1^1<<MUX0;              // select ADC3 (PB3)
  wait7();
  if( ACSR & 1<<ACO )
    keys |= 1<<3;

  ADMUX = 1<<MUX1;                      // select ADC2 (PB4)
  wait7();
  if( ACSR & 1<<ACO )
    keys |= 1<<4;

  PORTB = saveport;                     // restore outputs
  DDRB = 0xFF;

  return keys;
}


static void key_poll( void )
{
  static uint8_t ct0 = 0xFF, ct1 = 0xFF;
  uint8_t i;

  i = key_state ^ scan_tast();          // key changed ?
  ct0 = ~( ct0 & i );                   // reset or count ct0
  ct1 = ct0 ^(ct1 & i);                 // reset or count ct1
  i &= ct0 & ct1;                       // count until roll over ?
  key_state ^= i;                       // then toggle debounced state
  key_press |= key_state & i;           // 0->1: key press detect
}


static uint8_t get_key_press( uint8_t key_mask )
{
//  cli();
  key_mask &= key_press;                // read key(s)
  key_press ^= key_mask;                // clear key(s)
//  sei();
  return key_mask;
}


int main( void )
{
  DDRB = 0xFF;
  PORTB = 0;

  for(;;){
    _delay_ms(10);                      // debouncing time
    key_poll();
    PORTB ^= get_key_press( 0xFF );     // toggle on key press
  }
}