//
// hello.ESC.44.c
//
// electronic speed controller hello-world, tiny44 version
//    16-bit PWM, 115200 baud FTDI character echo
//    set lfuse to 0x5E for 20 MHz xtal
//
// Neil Gershenfeld
//    11/4/19
//
// 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>
#include <stdlib.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
#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 serial_port PORTA
#define serial_direction DDRA
#define serial_pins PINA
#define serial_pin_out (1 << PA1)
#define serial_pin_in (1 << PA0)
#define PWM_port PORTA
#define PWM_pin (1 << PA6)
#define PWM_direction DDRA

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) {
   //
   // main
   //
   char str[4];
   uint16_t value;
   //
   // set clock divider to /1 (8 MHz)
   //
   CLKPR = (1 << CLKPCE);
   CLKPR = (0 << CLKPS3) | (0 << CLKPS2) | (0 << CLKPS1) | (0 << CLKPS0);
   //
   // initialize comm pins
   //
   set(serial_port,serial_pin_out);
   output(serial_direction,serial_pin_out);
   input(serial_direction,serial_pin_in);
   //
   // set up timer 1
   //
   TCCR1A = (1 << COM1A1) | (0 << COM1A0); // clear OC1A on compare match
   TCCR1B = (0 << CS12) | (1 << CS11) | (0 << CS10) | (1 << WGM13); // prescaler /8, phase and frequency correct PWM, ICR1 TOP
   ICR1 = 25000; // 20 ms PWM frequency
   OCR1A = 1250; // 1 ms PWM pulse
   //
   // initialize PWM pin
   //
   clear(PWM_port,PWM_pin);
   output(PWM_direction,PWM_pin);
   //
   // main loop
   //
   while (1) {
      put_string(&serial_port,serial_pin_out,"PWM value (1250-2500)? ");
      get_char(&serial_pins,serial_pin_in,&str[0]);
      put_char(&serial_port,serial_pin_out,str[0]);
      get_char(&serial_pins,serial_pin_in,&str[1]);
      put_char(&serial_port,serial_pin_out,str[1]);
      get_char(&serial_pins,serial_pin_in,&str[2]);
      put_char(&serial_port,serial_pin_out,str[2]);
      get_char(&serial_pins,serial_pin_in,&str[3]);
      put_char(&serial_port,serial_pin_out,str[3]);
      put_char(&serial_port,serial_pin_out,10); // new line
      value = atoi(str);
      if ((value < 1250) || (value > 2500)) {
         put_string(&serial_port,serial_pin_out,"   out of range 1-2 ms");
         put_char(&serial_port,serial_pin_out,10);
         }
      else {
         OCR1A = atoi(str);
         put_string(&serial_port,serial_pin_out,"   updated");
         put_char(&serial_port,serial_pin_out,10);
         }
      }
   }