#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 24 // bit delay for 38400 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 PWM_delay() _delay_us(1) // PWM unit delay
#define PWM_period 100

#define serial_port PORTA
#define serial_direction DDRA
#define serial_pin_out (1 << PA1)
#define in_port PORTA
#define in_direction DDRA
#define in_pins PINA
#define x_pin (1 << PA7)
#define bridge_port PORTA // H-bridge port
#define bridge_direction DDRA // H-bridge direction
#define IN1 (1 << PA3) // IN1
#define IN2 (1 << PA2) // IN2
#define ACCEL_SAMPLES 3

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 pwm_break(uint16_t iters, uint16_t PWM_duty) {
	static uint16_t PWM_count;
    static uint16_t i;
    for (i = 0; i <= iters; ++i){
            // forward at given duty cycle
            clear(bridge_port, IN2);
            for (PWM_count = 0; PWM_count < PWM_duty; ++PWM_count)
                PWM_delay();
            set(bridge_port, IN2);
            for (PWM_count = 0; PWM_count < PWM_period - PWM_duty; ++PWM_count)
                PWM_delay();
        }
}

int main(void) {
	//
	// main
	//
    static uint16_t i;
    static uint16_t xoff,xon;
	static uint16_t PWM_duty = 50;
        
	//
	// set clock divider to /1 (8 MHz)
	//
	CLKPR = (1 << CLKPCE);
	CLKPR = (0 << CLKPS3) | (0 << CLKPS2) | (0 << CLKPS1) | (0 << CLKPS0);
	//
	// initialize H-bridge pins
	//
	clear(bridge_port, IN1);
	output(bridge_direction, IN1);
	clear(bridge_port, IN2);
	output(bridge_direction, IN2);

	clear(bridge_port, IN1);
	set(bridge_port, IN2);
    
    //
    // initialize serial output pins
    //
    set(serial_port, serial_pin_out);
    output(serial_direction, serial_pin_out);
 	 
    //
    // main loop
    //
    while (1) {
        // 
        // read x (approximate loop timing)
        //
        xoff = 0;
        xon = 0;
        for (i = 0; i < ACCEL_SAMPLES; ++i) {
            //
            // wait for x high 
            //
            while (0 == pin_test(in_pins,x_pin))
                pwm_break(1, PWM_duty);
            //
            // wait for x low
            //
            while (0 != pin_test(in_pins,x_pin))
                pwm_break(1, PWM_duty);
            //
            // time x low 
            //
            while (0 == pin_test(in_pins,x_pin)){
                xoff += 1;
                pwm_break(1, PWM_duty);
            }
            //
            // time x high
            //
            while (0 != pin_test(in_pins,x_pin)) {
                xon += 1;
                pwm_break(1, PWM_duty);
            }
        }
        //
        // send framing
        //
        put_char(&serial_port, serial_pin_out, 1);
        put_char(&serial_port, serial_pin_out, 2);
        put_char(&serial_port, serial_pin_out, 3);
        put_char(&serial_port, serial_pin_out, 4);
        //
        // send x
        //
        put_char(&serial_port, serial_pin_out, (xoff & 255));
        put_char(&serial_port, serial_pin_out, ((xoff >> 8) & 255));
        put_char(&serial_port, serial_pin_out, (xon & 255));
        put_char(&serial_port, serial_pin_out, ((xon >> 8) & 255));
        
        pwm_break(10, PWM_duty);
	}
}