/************************************************************************/
/*                                                                      */
/*                      Key + LED over the same wire (4*)               */
/*                                                                      */
/*              Author: P. Dannegger                                    */
/*                                                                      */
/************************************************************************/
#include <io.h>


typedef unsigned char  u8;
typedef   signed char  s8;
typedef unsigned short u16;
typedef   signed short s16;
typedef unsigned long  u32;
typedef   signed long  s32;


#define NADA()	  asm volatile(""::)	// do nothing, but immediately

#define NOIL(fkt) __attribute__ ((noinline)) fkt; fkt


u8 key_state;				// debounced key state:
					// bit = 1: key pressed
u8 key_press;				// key press detect


static void wait10ms( void )		// static to avoid code doubling !
{
  u16 i = 20000;			// 10ms at 8MHz

  do
    NADA();
  while( --i );
}


NOIL( void wait7( void))		// 7 cycle
{
  NADA();				// avoid removing completely !
}


static u8 scan_tast( void )
{
  u8 saveport = PORTB;
  u8 keys = 7;				// >= 7 to avoid loop unrolling !

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

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

  do					// time to pull up released keys
    NADA();
  while( --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 u8 ct0 = 0xFF, ct1 = 0xFF;
  u8 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 u8 get_key_press( u8 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(;;){
    wait10ms();				// debouncing time
    key_poll();
    PORTB ^= get_key_press( 0xFF );	// toggle on key press
  }
}