//
//
// hello.reflect.45.c
//
// light reflection synchronous detection hello-world
//    9600 baud FTDI interface
//
// Neil Gershenfeld
// 10/25/12
//
// (c) Massachusetts Institute of Technology 2012
// 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>

#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 102 // 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 char_delay() _delay_ms(10) // char delay

#define serial_port PORTB
#define serial_direction DDRB
#define serial_pin_out (1 << PB2)

#define led_port PORTB
#define led_direction DDRB
#define led_pin (1 << PB3)

#define nloop 100 // number of loops to accumulate

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();
   //
   // char delay
   //
   bit_delay();
   }

int main(void) {
   //
   // main
   //
   static unsigned char count;
   static uint16_t on,off;
   //
   // 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);
   set(led_port, led_pin);
   output(led_direction, led_pin);
   //
   // init A/D
   //
   ADMUX = (0 << REFS2) | (0 << REFS1) | (0 << REFS0) // Vcc ref
      | (0 << ADLAR) // right adjust
      | (0 << MUX3) | (0 << MUX2) | (1 << MUX1) | (0 << MUX0); // ADC2
   ADCSRA = (1 << ADEN) // enable
      | (1 << ADPS2) | (1 << ADPS1) | (1 << ADPS0); // prescaler /128
   //
   // main loop
   //
   while (1) {
      //
      // accumulate
      //
      on = 0;
      off = 0;
      for (count = 0; count < nloop; ++count) {
         //
         // LED off
         //
         set(led_port, led_pin);
         //
         // initiate conversion
         //
         ADCSRA |= (1 << ADSC);
         //
         // wait for completion
         //
         while (ADCSRA & (1 << ADSC))
            ;
         //
         // save result
         //
         off += ADC;
         //
         // LED on
         //
         clear(led_port, led_pin);
         //
         // initiate conversion
         //
         ADCSRA |= (1 << ADSC);
         //
         // wait for completion
         //
         while (ADCSRA & (1 << ADSC))
            ;
         //
         // save result
         //
         on += ADC;
         }
      //
      // send framing
      //
      put_char(&serial_port, serial_pin_out, 1);
      char_delay();
      put_char(&serial_port, serial_pin_out, 2);
      char_delay();
      put_char(&serial_port, serial_pin_out, 3);
      char_delay();
      put_char(&serial_port, serial_pin_out, 4);
      char_delay();
      //
      // send result
      //
      put_char(&serial_port, serial_pin_out, (on & 255));
      char_delay();
      put_char(&serial_port, serial_pin_out, ((on >> 8) & 255));
      char_delay();
      put_char(&serial_port, serial_pin_out, (off & 255));
      char_delay();
      put_char(&serial_port, serial_pin_out, ((off >> 8) & 255));
      char_delay();
      }
   }