On the first two chapters of this Tutorial we started with a simple LFSR module and added a test bench. Then, on chapters three and four we upgraded our module with some features and learned to export the test bench data to files.
Chapter 5 – Matlab Formal Verification
Our VHDL block implements an algorithm that generates pseudo-random numbers. If the register is large enough, the output of the block will be hundreds or thousands of different numbers. How can we be sure that our block is working OK?
“Field programmable gate arrays (FPGAs) are increasingly complex system on chips (SoCs) that include not just programmable logic gates and random access memory (RAM) but also analog-to-digital converters (ADCs); digital-to-analog converters (DACs); and programmable analog features and signal-conditioning circuits that enable high-performance digital computations in servers, network-attached storage (NAS), enterprise switches, oscilloscopes, network analyzers, test equipment and software-defined radios.”
Adam Taylor is the well known author of the MicroZed Chronicles blog on Xilinx website. His Chronicles have been running for several years, and Adam has already compiled entries from his blog in two books. The first book is offered for free on the FPGARelated website for registered users.
On the first part of this tutorial, we started with a simple implementation of an LFSR block (Chapter 1) and it test bench (Chapter 2). Let’s make our code a bit more professional.
Chapter 3 – Upgrading the LFSR code
Good code doesn’t use hard-coded constants as were used on the first part (to define the LFSR width). The downside of using constants is that code updates and maintenance is cumbersome at best. If we want to change the width of the register… we must scan the code and change each and every instance of the constant. There is a great possibility of making mistakes while doing that. Forgetting to change one of the ‘3’s… or changing one that was not related to the register width. This is not clearly seen in a short piece of code, but as our code gets longer, maintaining hard-coded constants is a sure recipe for trouble.
In this tutorial we will see how to design a block. We will start with a very simple block and gradually add features to it. We will also simulate it and test its output with Matlab. Over the process we will see:
How to start with a simple block and gradually add features and improvements
How to add a test bench (simulation)
Adding parameters to the VHDL block
Saving the block data output to files (from simulation)