//
//
// phil_hello.ftdi.44.echo.interrupt.c
//
// 115200 baud FTDI character echo, interrupt version
//
// set lfuse to 0x5E for 20 MHz xtal
//
// Neil Gershenfeld
// 12/8/10

// Modified and debugged by F. Phil Brooks III
// 10/23/19
// Harvard Chemistry and Chemical Biology
//
// (c) Massachusetts Institute of Technology 2010
// This work may be reproduced, modified, distributed,
// performed, and displayed for any purpose. Copyright is
// retained and must be preserved. The work is provided
// as is; no warranty is provided, and users accept all 
// liability.
//

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


#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 serial_pin_in (1 << PA0)
#define serial_pin_out (1 << PA1)
#define serial_interrupt (1 << PCIE0)
#define serial_interrupt_pin (1 << PCINT0)
#define serial_interrupt_flag (1 << PCIF0) //needed to clear flag

#define button_interrupt (1 << PCIE1)
#define button_interrupt_pin (1 << PCINT10)
#define button_interrupt_flag (1 << PCIF1)
#define button_pin (1 << PB2)

#define led_pin (1 << PA7)


#define max_buffer 10 //can be raised as long as it fits in chip memory. This is low for demonstration of buffer filling.

char buffer[max_buffer] = {0};
int buffer_index = 0;

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 (*pins & pin)
      //
      // wait for start bit
      //
      ;
   //
   // delay to middle of first data bit
   //
   //half_bit_delay(); //causes problems receiving o, w with fixed code. May have been legacy of bug.
   bit_delay();
   //
   // unrolled loop to read data bits
   //
   if (*pins & pin)
      *rxbyte |= (1 << 0);
   else
      *rxbyte |= (0 << 0);
   bit_delay();
   if (*pins & pin)
      *rxbyte |= (1 << 1);
   else
      *rxbyte |= (0 << 1);
   bit_delay();
   if (*pins & pin)
      *rxbyte |= (1 << 2);
   else
      *rxbyte |= (0 << 2);
   bit_delay();
   if (*pins & pin)
      *rxbyte |= (1 << 3);
   else
      *rxbyte |= (0 << 3);
   bit_delay();
   if (*pins & pin)
      *rxbyte |= (1 << 4);
   else
      *rxbyte |= (0 << 4);
   bit_delay();
   if (*pins & pin)
      *rxbyte |= (1 << 5);
   else
      *rxbyte |= (0 << 5);
   bit_delay();
   if (*pins & pin)
      *rxbyte |= (1 << 6);
   else
      *rxbyte |= (0 << 6);
   bit_delay();
   if (*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
   //
   *port &= (~pin);
   bit_delay();
   
   //
   // unrolled loop to write data bits
   //
   if (txchar & (1<<0))
      *port |= pin;
   else
      *port &= (~pin);
   bit_delay();
   if (txchar & (1<<1))
      *port |= pin;
   else
      *port &= (~pin);
   bit_delay();
   if (txchar & (1<<2))
      *port |= pin;
   else
      *port &= (~pin);
   bit_delay();
   if (txchar & (1<<3))
      *port |= pin;
   else
      *port &= (~pin);
   bit_delay();
   if (txchar & (1<<4))
      *port |= pin;
   else
      *port &= (~pin);
   bit_delay();
   if (txchar & (1<<5))
      *port |= pin;
   else
      *port &= (~pin);
   bit_delay();
   if (txchar & (1<<6))
      *port |= pin;
   else
      *port &= (~pin);
   bit_delay();
   if (txchar & (1<<7))
      *port |= pin;
   else
      *port &= (~pin);
   bit_delay();
   //
   // stop bit
   //
   *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;
   get_char(&PINA, serial_pin_in, &chr);

   put_string(&PORTA, serial_pin_out, "hello.ftdi.44.echo.interrupt.c: you typed \"");
   buffer[buffer_index++] = chr;
   if (buffer_index == (max_buffer-1)) { //last char is always null (necessary for put_string).
	  PORTA |= led_pin; //turn on LED if buffer is full.
      buffer_index = 0;
   }
   put_string(&PORTA, serial_pin_out, buffer);
   put_char(&PORTA, serial_pin_out, '\"');
   put_char(&PORTA, serial_pin_out, 10); // new line
   GIFR = serial_interrupt_flag; //clear pending serial interrupts caused by data transmission.
}
ISR(PCINT1_vect) {
	//button press interrupt handler
	
	//clear buffer
	for (int i = 0; i < max_buffer; i++) {
		buffer[i]= 0;
	}
	//send cleared message
	put_string(&PORTA, serial_pin_out, "Buffer Cleared\n");
	buffer_index = 0; //reset buffer index.
	PORTA &= (~led_pin); //turn off LED
	GIFR = button_interrupt_flag; //clear button interrupt flag 
	//(catches bouncing, but not release of button, since 
	// user release of button is much slower than this interrupt handler.
}


int main(void) {
   //
   // main
   //
   // set clock divider to /1
   //
   CLKPR = (1 << CLKPCE);
   CLKPR = (0 << CLKPS3) | (0 << CLKPS2) | (0 << CLKPS1) | (0 << CLKPS0);
   //
   // initialize output pins
   //
   PORTA |= serial_pin_out;
   PORTA &= (~led_pin); //make sure LED is off.
   PORTB |= button_pin; //turn on pull-up resistor
   DDRA |= serial_pin_out;
   DDRA |= led_pin; //make LED pin an output able to source current.
   //
   // set up pin change interrupt on input pin
   //
   GIMSK |= serial_interrupt;
   GIMSK |= button_interrupt; //enable PCINT1 interrupts
   PCMSK0 |= serial_interrupt_pin;
   PCMSK1 |= button_interrupt_pin; //enable PCTINT10 to trigger PCINT1
      
   sei();
   //
   // main loop
   //
   while (1) {
      //
      // wait for interrupt
      //
	  ;
      }
   }