How to stop simulation in a VHDL testbench

How to Stop Simulation in a VHDL Testbench

How do you stop the VHDL simulator when the simulation is complete? There are several ways to do that. In this article, we will examine the most common ways to end a successful testbench run.

The VHDL code presented here is universal, and it should work in any capable VHDL simulator. For the methods involving Tcl, I will list the commands for the ModelSim and Vivado simulators.

You can download an example project with the four different testbenches from this article if you have ModelSim installed.

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Clk’event vs rising_edge

(clk'event and clk = '1') vs rising_edge(clk)

When you have worked with VHDL code written by many other FPGA engineers, you are bound to notice that there are two common ways to model an edge detector in VHDL. There’s the rising_edge(clk) statement, and there’s the old style clk’event and clk = ‘1’ method.

The two if-statements do the same thing once the code is on the FPGA. They postulate that whatever is inside of the if-statement happens on the rising edge of the trigger signal,

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Make Lattice iCEcube2 work on Ubuntu 20.04 and program the iCEstick FPGA board

Lattice iCEcube2 running in Ubuntu 20.04

This tutorial shows how to install the Lattice iCEcube2 FPGA design software on Ubuntu 20.04. Instead of the Lattice Diamond Programmer, we will use the alternative programmer from Project IceStorm that works flawlessly on Ubuntu Linux.

The Lattice iCEcube2 FPGA design software only works on Red Hat-based Linux distributions out of the box. Fortunately, we can make it run perfectly on Ubuntu Linux by installing dependencies and making a few changes to our system.

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How to create a breathing LED effect using a sine wave stored in block RAM

Sine wave

I’ve noticed that many of the gadgets that I’ve bought the last couple of years have shifted away from LED blinking to led breathing. Most electronic gizmos contain a status LED whose behavior gives away indications of what’s going on inside of the device.

My electric toothbrush flashes an LED when it’s time to recharge it, and my mobile phone uses the LED to call my attention for a wide variety of reasons.

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How to create a PWM controller in VHDL

PWM simulation in ModelSim waveform

Pulse-width modulation (PWM) is an efficient way to control analog electronics from purely digital FPGA pins. Instead of attempting to regulate the analog voltage, PWM rapidly switches on and off the supply current at full power to the analog device. This method gives us precise control over the moving average of energy provided to the consumer device.

Examples of use cases that are good candidates for PWM are audio modulation (speakers), light intensity control (lamps or LEDs),

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How to make ModelSim from Quartus Prime Lite work on Ubuntu 20.04

ModelSim-Intel FPGA Edition running in Ubuntu 20.04

The ModelSim version that comes with Intel Quartus Prime Lite Edition is a good alternative if you want to try out VHDL simulation on your home computer. The software is available for both Windows and Linux, but Intel only supports Red Hat-based distros like CentOS Linux.

Fortunately, you are just a few hacks away from ModelSim working nicely on your Ubuntu box.

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Using variables for registers or memory in VHDL

Variables used as registers in VHDL

One question that I’ve debated many times over the years is whether it’s OK to use variables for registers in VHDL. It’s safe to say that newbies are more likely to do it than experienced VHDL designers. But is there any merit to that, or is it just a matter of preference?

In this blog post, I will try to shed some light on the issue so that you can make an informed decision about using this design practice.

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Jenkins for FPGA projects using Vivado and GitHub on a Linux VPS

Jenkins automation server front page

This tutorial teaches you how to set up an automation server on a Virtual Private Server (VPS) using Jenkins, Xilinx Vivado, and the Git / GitHub source-control management (SCM) system.

Jenkins can be a valuable tool also for FPGA teams. Automating tasks can save your company time and improve the quality of your code. By using automatic build triggers and automated job pipelines, fewer coding errors will go unnoticed.

Should you use an FPGA or a microcontroller?

FPGA or Microcontroller

Many people turn to me for advice regarding their FPGA projects. Often, my answer is not what they expected: have you considered using a microcontroller instead of an FPGA?

I’m running VHDLwhiz, the website dedicated to FPGA design using VHDL. My life revolves around FPGAs, and I’m the biggest proponent of VHDL there is. Why would I say such a thing?

It’s because, for some tasks, an FPGA is overkill.

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Dual 7-segment display FPGA controller

7-segment display

In this article, I will present a VHDL module that can display a two-digit number on the Pmod SSD: Seven-segment Display from Digilent. The dual 7-segment display is compatible with the Pmod interface, meaning that you can use it without any soldering. It fits into the Pmod connector, which is standard on many FPGA development boards.