"V-USB is a software-only implementation of a low-speed USB device for Atmel’s AVR® microcontrollers, making it possible to build USB hardware with almost any AVR® microcontroller, not requiring any additional chip."
V-USB uses a set of hardware and some very special assembly programming techniques to bit-bang the non-return-to-zero (NRZ) binary code that USB uses to communicate. The files provided by V-USB will be compiled into our program in order to create a USB device with our ATmega328P
Please visit the download section of V-USB's website to obtain a copy of the latest version. In my project source code, it's already included.
To compile V-USB into your project...