/******************************************************************************************
* button_brd.c
*
* based on hello.ftdi.c by Neil Gershenfeld
*      and button44 by Rob Hart
* set lfuse to 0x5E for 20 MHz xtal
*
* Debounces button inputs and sends the count over serial
*
* Brian Plancher
* 11/21/16
*
********************************************************************************************/

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

// helper defs
#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 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

// serial port
#define serial_port PORTA
#define serial_direction DDRA
#define serial_pins PINA
#define serial_pin_in (1 << PA0)
#define serial_pin_out (1 << PA1)

// input devices
// Button  PB2
#define input_port PORTB
#define input_direction DDRB
#define input_pins PINB
#define button_pin (1 << PB2)

// for debounce
#define XTAL		      20000000L    // Crystal frequency in Hz
#define OUTER_LOOPS     2000
#define INNER_LOOPS     (XTAL / OUTER_LOOPS / 750)
#define MAX_COUNT       32767
#define MAX_COUNT_SIZE  15

// for serial comms
#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();
   //
   // char delay
   //
   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);
   }
   
int main(void) {
   // 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 buttons
   set(input_port, button_pin); // turn on pull-up for the buttons
   input(input_direction, button_pin); // make button input
   volatile uint16_t inner_loop_cntr = 0;
   volatile uint16_t outer_loop_cntr = 0;
   volatile uint8_t btn_state = 0;
   volatile uint8_t btn_hold = 0;
   
   // main loop
   while (1) {
      // debounce the button inputs
      volatile uint8_t btn_flag = !pin_test(input_pins,button_pin); // invert b/c pullup
      if(!btn_flag){
         btn_hold = 0;
      }
      if(!btn_hold){
         if (btn_state != btn_flag){
             btn_state = btn_flag;
             inner_loop_cntr = 0;
             outer_loop_cntr = 0;
         }      
         if (outer_loop_cntr == OUTER_LOOPS){
             outer_loop_cntr = 0;
             // see if majority of count was a bttn press
             if (btn_state){
                btn_hold = 1;
               // notify over serial
               put_char(&serial_port, serial_pin_out, 'A');
             }
         }
         else{
            if (inner_loop_cntr == INNER_LOOPS){
                inner_loop_cntr = 0;
                outer_loop_cntr += 1;
            }
            else{
                inner_loop_cntr++;
            }
         }
      }  
   }
}