External IO and Metastability
If you’ve gone through the first couple of Alchitry tutorials, you may have been wondering how the inputs and outputs of the top-level module know where to connect on the board. What about the LED name tells the tools what pin on the FPGA to use? Well wonder no more! In this tutorial I’m going to explain the basics of constraint files and dive into some of the dangers of using external signals in your designs.
This tutorial is primarily conceptual, but if you'd like to follow along, you'll need the following materials.
If you aren’t familiar with the following concepts, we recommend checking out these tutorials before continuing.