AVR-C code + makefile. See: http://fab.cba.mit.edu/classes/863.15/section.CBA/people/Schaad/week9-output-devices.html

att45_schaad1.c

//
//  att45_schaad1.c
//
//  Created by Raphael Schaad on 2015-11-16.
//  This is free and unencumbered software released into the public domain.
//

// Import headers installed with CrossPack-AVR (/usr/local/CrossPack-AVR/)
#include "stdbool.h" // So we have 'true' and 'false' instead of 1 and 0 (might have memory implications) -- lib/gcc/avr/4.8.1/include/
#include <avr/io.h> // Umbrella header including e.g. iotn45.h for our chip, defining PORTB/DDRB/PBn -- avr/include/avr/
#include <util/delay.h> // _delay_us/ms convenience functions for actual time values rather than number of cycles -- avr/include/util

// Hardware:
// Based on Neil Gershenfeld's board: http://academy.cba.mit.edu/classes/output_devices/H-bridge/hello.H-bridge.44.png
// With my redesign and enhancements: http://fab.cba.mit.edu/classes/863.15/section.CBA/people/Schaad/week9-output-devices.html
#define BTN1     (1 << PB2) // left   (pin 7)
#define BTN2     (1 << PB3) // center (pin 2)
#define BTN3     (1 << PB4) // right  (pin 3)
#define MOTORCCW (1 << PB0) // IN1    (pin 5)
#define MOTORCW  (1 << PB1) // IN2    (pin 6)

// Convenience macros
#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

// Bootloader calls main(void) when the chip gets power
int main() {
   // Configure digital I/O pins DDRB (bits are 0-based index)
   output(DDRB, MOTORCCW);
   output(DDRB, MOTORCW);

   // For input, also turn on pullup resistors with set(PORTB, BTNn)
   input(DDRB, BTN1);
   set(PORTB, BTN1);

   input(DDRB, BTN2);
   set(PORTB, BTN2);

   input(DDRB, BTN3);
   set(PORTB, BTN3);

   // PWM to slow motor down
   const double kPWMOnDuration = 1.0; // in ms
   const double kPWMSleepDuration = 10.0; // in ms
   bool motorCWOn = false;
   bool motorCCWOn = false;

   // Spin event loop
   while (true) {
      if (motorCWOn) {
         set(PORTB, MOTORCW);
         _delay_ms(kPWMOnDuration);
         clear(PORTB, MOTORCW);
         _delay_ms(kPWMSleepDuration);
      } else {
         clear(PORTB, MOTORCW);
      }

      if (motorCCWOn) {
         set(PORTB, MOTORCCW);
         _delay_ms(kPWMOnDuration);
         clear(PORTB, MOTORCCW);
         _delay_ms(kPWMSleepDuration);
      } else {
         clear(PORTB, MOTORCCW);
      }

      // Once center button is pressed, turn motor CW.
      if (!pin_test(PINB, BTN2)) {
         motorCWOn = true;
      }

      // Once right button is hit, turn motor off.
      if (!pin_test(PINB, BTN3)) {
         motorCWOn = false;
         // Clear immediately because of following delay stalling the event loop.
         clear(PORTB, MOTORCW);
         // Lift flag off the right button by turning motor back CCW just a bit.
         const unsigned int kCount = 30;
         unsigned int i;
         for (i = 0; i < kCount; ++i) {
            set(PORTB, MOTORCCW);
            _delay_ms(kPWMOnDuration);
            clear(PORTB, MOTORCCW);
            _delay_ms(kPWMSleepDuration);
         }

         // Wait for 7 seconds, and turn motor back CCW.
         _delay_ms(7000.0);
         motorCCWOn = true;
      }

      // Once left button is hit, turn motor off.
      if (!pin_test(PINB, BTN1)) {
         motorCCWOn = false;
      }
   }

   // When main(void) exits, the chip goes idle
   return 0;
}

att45_schaad1.make

#
#  att45_schaad1.make
#
#  Created by Raphael Schaad on 2015-11-16.
#  This is free and unencumbered software released into the public domain.
#

PROJECT=att45_schaad1
SOURCES=$(PROJECT).c
MMCU=attiny45

CFLAGS=-mmcu=$(MMCU) -Wall -Os

$(PROJECT).hex: $(PROJECT).out
	avr-objcopy -O ihex $(PROJECT).out $(PROJECT).c.hex;\
	avr-size --mcu=$(MMCU) --format=avr $(PROJECT).out

$(PROJECT).out: $(SOURCES)
	avr-gcc $(CFLAGS) -I./ -o $(PROJECT).out $(SOURCES)

program-usbtiny: $(PROJECT).hex
	avrdude -p t45 -P usb -c usbtiny -U flash:w:$(PROJECT).c.hex