//
// hello.HC-SR501.c
//
// HC-SR501 motion detector hello-world
//    9600 baud FTDI interface
//
// Neil Gershenfeld 11/16/15
// (c) Massachusetts Institute of Technology 2015
//
// 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 out_pins PINB
//#define out_pin (1 << PB4)

#define piezo_pin (1 << PB3)

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 char chrl;
  static char chrh;

  // set clock divider to /1
  CLKPR = (1 << CLKPCE);
  CLKPR = (0 << CLKPS3) | (0 << CLKPS2) | (0 << CLKPS1) | (0 << CLKPS0);

  // initialize serial pin
  set(serial_port, serial_pin_out);
  output(serial_direction, serial_pin_out);

  // init A/D
  ADMUX = (0 << REFS2) | (0 << REFS1) | (0 << REFS0) // Vcc ref
          | (0 << ADLAR) // right adjust
          | (0 << MUX3) | (0 << MUX2) | (1 << MUX1) | (1 << MUX0); // ADC3
  ADCSRA = (1 << ADEN) // enable
           | (1 << ADPS2) | (1 << ADPS1) | (1 << ADPS0); // prescaler /128

  // main loop
  while (1) {
    // 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();

    // initiate conversion
    ADCSRA |= (1 << ADSC);

    // wait for completion voltage analog -> digital
    while (ADCSRA & (1 << ADSC));

    // send result
    chrl = ADCL;
    put_char(&serial_port, serial_pin_out, chrl);
    char_delay();
    chrh = ADCH;
    put_char(&serial_port, serial_pin_out, chrh);
    char_delay();

  }
}