#ifndef F_CPU
#define F_CPU 16000000UL
#endif

#include <avr/io.h>
#include <util/delay.h>
#define BMP 0x76
static void twi_init(void){ TWSR=0; TWBR=72; }
static void tw(uint8_t d){ TWDR=d; TWCR=(1<<TWINT)|(1<<TWEN); while(!(TWCR&(1<<TWINT))); }
static void start(void){ TWCR=(1<<TWINT)|(1<<TWSTA)|(1<<TWEN); while(!(TWCR&(1<<TWINT))); }
static void stop(void){ TWCR=(1<<TWINT)|(1<<TWSTO)|(1<<TWEN); }
static uint8_t rd(uint8_t a){ TWCR=(1<<TWINT)|(1<<TWEN)|(a?(1<<TWEA):0); while(!(TWCR&(1<<TWINT))); return TWDR; }
static void wreg(uint8_t r,uint8_t v){ start(); tw(BMP<<1); tw(r); tw(v); stop(); }
static uint8_t rreg(uint8_t r){ start(); tw(BMP<<1); tw(r); start(); tw((BMP<<1)|1); uint8_t v=rd(0); stop(); return v; }
int main(void){
  twi_init(); DDRB|=(1<<PB5);
  uint8_t id=rreg(0xD0);
  wreg(0xF4,0x27); wreg(0xF5,0xA0);       // normal mode, oversampling
  for(;;){
    uint32_t praw=((uint32_t)rreg(0xF7)<<12)|((uint32_t)rreg(0xF8)<<4)|(rreg(0xF9)>>4);
    if(id==0x58 && praw) PORTB^=(1<<PB5);
    _delay_ms(200);
  }
}