//
//
// hello.ftdi.44.echo.interrupt.c
//
// 115200 baud FTDI character echo, interrupt version
//
// set lfuse to 0x7E for 20 MHz xtal
//
// Neil Gershenfeld
// 12/8/10
//
// (c) Massachusetts Institute of Technology 2010
// Permission granted for experimental and personal use;
// license for commercial sale available from MIT.
//

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

#define output(directions,pin) (directions |= pin) // set port direction for output
#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 8.5 // bit delay for 115200 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 char_delay() _delay_ms(10) // char delay

#define serial_port PORTA
#define serial_direction DDRA
#define serial_pins PINA
#define serial_pin_in (1 << PA0)
#define serial_pin_out (1 << PA1)
#define serial_interrupt (1 << PCIE0)
#define serial_interrupt_pin (1 << PCINT0)

#define max_buffer 25

void get_char(volatile unsigned char *pins, unsigned char pin, char *rxbyte) {
   //
   // read character into rxbyte on pins pin
   //    assumes line driver (inverts bits)
   //
   *rxbyte = 0;
   while (pin_test(*pins,pin))
      //
      // 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(*pins,pin)
      *rxbyte |= (1 << 0);
   else
      *rxbyte |= (0 << 0);
   bit_delay();
   if pin_test(*pins,pin)
      *rxbyte |= (1 << 1);
   else
      *rxbyte |= (0 << 1);
   bit_delay();
   if pin_test(*pins,pin)
      *rxbyte |= (1 << 2);
   else
      *rxbyte |= (0 << 2);
   bit_delay();
   if pin_test(*pins,pin)
      *rxbyte |= (1 << 3);
   else
      *rxbyte |= (0 << 3);
   bit_delay();
   if pin_test(*pins,pin)
      *rxbyte |= (1 << 4);
   else
      *rxbyte |= (0 << 4);
   bit_delay();
   if pin_test(*pins,pin)
      *rxbyte |= (1 << 5);
   else
      *rxbyte |= (0 << 5);
   bit_delay();
   if pin_test(*pins,pin)
      *rxbyte |= (1 << 6);
   else
      *rxbyte |= (0 << 6);
   bit_delay();
   if pin_test(*pins,pin)
      *rxbyte |= (1 << 7);
   else
      *rxbyte |= (0 << 7);
   //
   // wait for stop bit
   //
   bit_delay();
   half_bit_delay();
   }

void put_char(volatile unsigned char *port, unsigned char pin, char txchar) {
   //
   // send character in txchar on port pin
   //    assumes line driver (inverts bits)
   //
   // start bit
   //
   clear(*port,pin);
   bit_delay();
   //
   // unrolled loop to write data bits
   //
   if bit_test(txchar,0)
      set(*port,pin);
   else
      clear(*port,pin);
   bit_delay();
   if bit_test(txchar,1)
      set(*port,pin);
   else
      clear(*port,pin);
   bit_delay();
   if bit_test(txchar,2)
      set(*port,pin);
   else
      clear(*port,pin);
   bit_delay();
   if bit_test(txchar,3)
      set(*port,pin);
   else
      clear(*port,pin);
   bit_delay();
   if bit_test(txchar,4)
      set(*port,pin);
   else
      clear(*port,pin);
   bit_delay();
   if bit_test(txchar,5)
      set(*port,pin);
   else
      clear(*port,pin);
   bit_delay();
   if bit_test(txchar,6)
      set(*port,pin);
   else
      clear(*port,pin);
   bit_delay();
   if bit_test(txchar,7)
      set(*port,pin);
   else
      clear(*port,pin);
   bit_delay();
   //
   // stop bit
   //
   set(*port,pin);
   bit_delay();
   }

void put_string(volatile unsigned char *port, unsigned char pin, char *str) {
   //
   // print a null-terminated string
   //
   static int index;
   index = 0;
   do {
      put_char(port, pin, str[index]);
      ++index;
      } while (str[index] != 0);
   }

ISR(PCINT0_vect) {
   
   // pin change interrupt handler
   static char chr;
   static char buffer[max_buffer] = {0};
   static int index;
   get_char(&serial_pins, serial_pin_in, &chr);
   put_string(&serial_port, serial_pin_out, "hello.ftdi.44.echo.interrupt.c: you typed \"");
   buffer[index++] = chr;
   if (index == (max_buffer-1))
      index = 0;
   put_string(&serial_port, serial_pin_out, buffer);
   put_char(&serial_port, serial_pin_out, '\"');
   put_char(&serial_port, serial_pin_out, 10); // new line
   put_char(&serial_port, serial_pin_out, 13); //carrage return 
   }

int main(void) {

   // main

   // 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);
   output(serial_direction, serial_pin_out);
   
   // initialize LED pins
   output(DDRA, (1 << PA7));
   output(DDRA, (1 << PA2));
   output(DDRA, (1 << PA3));
   
   // initialize button
   set(PORTB, (1 << PB2));
   
   // set up pin change interrupt on input pin
   set(GIMSK, serial_interrupt);
   set(PCMSK0, serial_interrupt_pin);
   sei();

   // main loop
   while (1) {
      
	  // wait for button to be pressed
      
      if (!pin_test(PINB,(1 << PB2))) { // checks if button is pressed
		_delay_ms(10); // delay to prevent de-bounce effect in button to LED
		
		if (pin_test(PORTA,(1 << PA3))) { // checks if blue light is on
			clear(PORTA, (1 << PA3)); // clear blue light
			set(PORTA, (1 << PA2)); // set red light
		}
        
		else {
			set(PORTA, (1 << PA3)); // set blue light
			clear(PORTA, (1 << PA2)); // clear blue light
		}
		
		while (!pin_test(PINB,(1 << PB2))) { // checks if button is still pressed
			_delay_ms(1);
		}
	 }
	  
	  
	 // keeps the green LED on
      set(PORTA, (0 << PA7));
	    
     }
   }