In our previous post we implemented the bare minimum required to get a USB device to enumerate with the host and laid the groundwork for adding actual communications to our device. In this post we will do just that by adding support Vendor Specific control transfers, allowing a Host to Write and Read data from the device.
In this multi-part series, we will explore USB implementation on AVR microcontrollers, starting with the basics of USB enumeration. USB can be found all around us in our everyday lives. It's in our phones, our computers, our cars, and even our home appliances. It's a ubiquitous standard that has been around for decades and is still going strong. However we often take it for granted as engineers and developers. Silicon vendors have made it so easy to get a device up and running with USB via their libraries and examples that we don't often think about what's going on under the hood.