The ATMEGA328P is the heart of the popular Arduino Uno. The Uno is traditionally programmed via a USB cable. If you want to go embedded - that is use the MCU in a project without the Uno PCB or secondary ATMEGA8U2 - you will have to program the chip without the USB interface. This is possible with the Raspberry Pi's GPIO header using the SPI communication pins. In this tutorial I show you how to compile and upload a sketch to an ATMEGA328P using your Raspberry Pi.