//
//
// If delta of pressure is higher than threshold, send signal to motherboard
//
// Seowoo Kim
// Dec 7, 2017
//
//

#include <avr/io.h>
#include <util/delay.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
//What is bit set?

// macros for txrx
#define bit_delay_time 102 // bit delay for 9600 with overhead
//Why bit delay?
#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 settle_delay() _delay_us(100) // settle delay
//What/why settle delay?
#define char_delay() _delay_ms(10) // char delay
#define nloop 100 // loops to accumulate


// port defintiions for txrx
#define serial_port PORTB
#define serial_direction DDRB
// PB2 is RXD signal; rx pin on ftdi header
#define serial_pin_out (1 << PB2)

#define transmit_port PORTB
#define transmit_direction DDRB
#define transmit_pin (1 << PB4)

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 up,down;
   static int16_t lastup,lastdown;
   static int16_t deltaup,deltadown;// to track changes between loops
   static int16_t diff;
   static uint16_t upS,downS;
   //
   // 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);
   clear(serial_direction, serial_pin_out);
   clear(transmit_port, transmit_pin);
   output(transmit_direction, transmit_pin);
   //
   // init A/D
   //
   ADMUX = (0 << REFS1) | (0 << REFS0) // Vcc ref as ADC voltage reference
      | (0 << ADLAR) // right adjust
   // Got rid of MUX4 and MUX5 b/c Attiny45 does not have them
      | (0 << MUX3) | (0 << MUX2) | (1 << MUX1) | (1 << MUX0); // Selecting PA3 as input to ADC
   ADCSRA = (1 << ADEN) // enable
      | (1 << ADPS2) | (1 << ADPS1) | (1 << ADPS0); // prescaler /128

   //
   // main loop
   //
   while (1) {
      //
      // accumulate
      //
      // We measure 100 times to get sqrat(100) = 10 times resolution
      up = 0;
      down = 0;

      clear(serial_direction, serial_pin_out);
      for (count = 0; count < nloop; ++count) { 
         //
         // settle, charge
         //
         settle_delay();
         set(transmit_port, transmit_pin);
         //
         // initiate conversion
         //
         ADCSRA |= (1 << ADSC);
         //
         // wait for completion
         //
         while (ADCSRA & (1 << ADSC))
            ;
         //
         // save result
         //
         up += ADC;
         //
         // settle, discharge
         //
         settle_delay();
         clear(transmit_port, transmit_pin);
         //
         // initiate conversion
         //
         ADCSRA |= (1 << ADSC);
         //
         // wait for completion
         //
         while (ADCSRA & (1 << ADSC))
            ;
         //
         // save result
         //
         down += ADC;
         }
      //
      diff = up-down;
      
      if(diff>10000){
         output(serial_direction, serial_pin_out);
         put_char(&serial_port, serial_pin_out, '1');
         char_delay();

      }
      else{

      }

   }
}