#include <avr/io.h>
#include <util/delay.h>
#include <avr/pgmspace.h>
#include <string.h>

#define output(directions,pin) (directions |= pin) // set port direction for output
#define input(directions,pin) (directions &= (~pin)) // set port direction for input
#define set(port,pin) (port |= pin) // set port pin
#define clear(port,pin) (port &= (~pin)) // clear port pin
#define pin_test(pins,pin) (pins & pin) // test for port pin
#define bit_test(byte,bit) (byte & (1 << bit)) // test for bit set
#define bit_delay_time 100 // bit delay for 9600 with overhead
#define bit_delay() _delay_us(bit_delay_time) // RS232 bit delay
#define half_bit_delay() _delay_us(bit_delay_time/2) // RS232 half bit delay
#define led_delay() _delay_ms(100) // LED flash delay

#define led_port PORTB
#define led_direction DDRB
#define led1_pin (1 << PB0)
#define led2_pin (1 << PB1)
#define led3_pin (1 << PB2)

#define serial_port PORTB
#define serial_direction DDRB
#define serial_pins PINB
#define serial_pin_in (1 << PB3)

// invert all clear/set for LED if it will go to GND instead of VCC

void get_char(volatile unsigned char port, unsigned char pin, char rxbyte) {
   //
   // read character into rxbyte on pins pin
   //    assumes line driver (inverts bits)
   //
   rxbyte = 0;
   while (pin_test(serial_pins,serial_pin_in))
      //
      // wait for start bit
      //
      ;
   //
   // delay to middle of first data bit
   //
   half_bit_delay();
   bit_delay();
   //
   // unrolled loop to read data bits
   //
   if pin_test(serial_pins,serial_pin_in)
      rxbyte |= (1 << 0);
   else
      rxbyte |= (0 << 0);
   bit_delay();
   if pin_test(serial_pins,serial_pin_in)
      rxbyte |= (1 << 1);
   else
      rxbyte |= (0 << 1);
   bit_delay();
   if pin_test(serial_pins,serial_pin_in)
      rxbyte |= (1 << 2);
   else
      rxbyte |= (0 << 2);
   bit_delay();
   if pin_test(serial_pins,serial_pin_in)
      rxbyte |= (1 << 3);
   else
      rxbyte |= (0 << 3);
   bit_delay();
   if pin_test(serial_pins,serial_pin_in)
      rxbyte |= (1 << 4);
   else
      rxbyte |= (0 << 4);
   bit_delay();
   if pin_test(serial_pins,serial_pin_in)
      rxbyte |= (1 << 5);
   else
      rxbyte |= (0 << 5);
   bit_delay();
   if pin_test(serial_pins,serial_pin_in)
      rxbyte |= (1 << 6);
   else
      rxbyte |= (0 << 6);
   bit_delay();
   if pin_test(serial_pins,serial_pin_in)
      rxbyte |= (1 << 7);
   else
      rxbyte |= (0 << 7);
   //
   // wait for stop bit
   //
   bit_delay();
   half_bit_delay();
   }

void flash() {
   //
   // LED flash delay
   //
   clear(led_port, led_pin);
   led_delay();
   set(led_port, led_pin);
   }

   int main(void) {
   //
   // main
   //
   static char chr;
   //
   // set clock divider to /1
   //
   CLKPR = (1 << CLKPCE);
   CLKPR = (0 << CLKPS3) | (0 << CLKPS2) | (0 << CLKPS1) | (0 << CLKPS0);
   //
   // initialize output pins
   //
   set(serial_port, serial_pin_out);
   input(serial_direction, serial_pin_out);
   set(led_port, led_pin);
   output(led_direction, led_pin);
   //
   // main loop
   //
   while (1) {
      get_char(serial_port, serial_pin_in, chr);
      if (chr == 4) {
         led_delay();
         flash();
         }
      }
   }