Nuts and Volts - February 2009

Wire-wrap and low cost TTL parts have made the puzzle-solving

fun of digital logic design accessible to hobbyists and engineers

everywhere. Although TTL works fine for small designs, it becomes

expensive and time consuming for larger designs. Field Programmable

Gate Arrays (FPGAs) contain thousands or millions of uncommited

gates and are almost ideal for large designs. The problem with FPGAs

is that you have to learn a design language (Verilog or VHDL) and that

in order to write even simple Verilog programs you need to set up a

fairly complex development environment. It is the latter problem —

the development environment — that this article addresses.

By Bob Smith

Iinstall the Xilinx FPGA design tools, how to use the Xilinx n this article, you'll see how to

command line tools to compile a Verilog or VHDL design, how to download the compiled code to an FPGA board, and how to automate the whole process using a “makefile.”

The Xilinx command line tools are the same for both Linux and Windows, making this article useful for almost anyone with a computer (including Mac users using a Linux virtual machine). The sample design for this article is a 28 bit counter which has the most significant eight bits visible on LEDs. It is counting transitions on a 12. 5 MHz clock giving the least significant LED a flash rate of about 6 Hz. The circuit has a counter reset line tied to a button.

The hardware used herein is the Demand Peripherals Baseboard-2 which has a Xilinx Spartan-3E, LEDs, buttons, and a USB interface for

downloads and user data. Since the Baseboard-2 is downloaded through a USB serial port, it doesn't require the expense and complexity of a separate JTAG dongle or the hassle of installing JTAG drivers — and not requiring them is particularly nice for Linux developers. (I helped design the Baseboard-2 and one of our major design goals was to allow USB serial downloads.)

Installing the Xilinx WebPACK Toolkit

Xilinx provides a set of free design tools, the WebPACK, that runs on both Windows and Linux. Xilinx supports the tools on Windows XP Professional and on recent versions of Red Hat Enterprise Linux and SUSE Linux. While not officially supported, WebPACK runs fine on XP Home Edition, Vista, and Ubuntu. To get the tools working on your system, you have to go through about a dozen web pages to start the WebPACK

download, wait for a 2.2 GB download, and then go through another dozen or so screens for the installation. It is tedious, but straightforward.

Start by going to the Xilinx download site at:

www.xilinx.com/

support/download/ index.htm. Skip the Search button and scroll directly down to click on the "Download ISE WebPACK" link. This will take you to a login page where you can select "Create Account" (since you probably don't already have a Xilinx account). You will receive an email message with a web link where you can go to finish the registration and to log in. After logging in for the first time, you're asked to provide more information. The Next button will take you to a screen that displays what Xilinx packages you are entitled to download. Select ISE WebPack10.1 and click on the Next button.