Xilinx and Nexys2 Tutorial

Kartik Mohanram

Dept. of Electrical and Computer Engineering

Rice University, Houston, TX

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Verilog synthesis+simulation with Xilinx

XilinxProject

NavigatorIcon

on yourDesktop

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Open a new project called decoder2to4

Choose a working directory(C:\...\decoder2to4) and name the

top level module there (decoder2to4)

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Device options, etc.The next step is to select the target device and

its specs from the board (Spartan3E, xc3s500e, fg320);to specify Verilog as the input HDL language

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Create a new top level moduledecoder2to4 in the project

Adding new Verilog source

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Initialize project directory

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Enter the source

Use bottom tabs to select the source file, key in the Verilog description, and save it

Design constraints+actions:synthesis+implementation,

bit-file generation, etc.

2-to-4 decoder example

Use case statement Note that output [3:0] y is

changed to output reg [3:0] y No Xilinx option to specify

this directly Hand-code as necessary

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User constraint file (UCF)

UCF file for I/O mapping The UCF allows us to leverage

the switches, LEDs, etc. on the board to interact with the implemented design (see documentation on 326 page too)

Add new source Mapping visible on board Sometime mis-marked Cross-check with manual

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UCF generation

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Add I/O constraints

The mapping assigns switch 1 (available on pin G18) to input W[0], etc. These mappings are visible on the board and also part of the Nexys2 board documentation.

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Compile! Select the decoder2to4 module and double-

click the “Synthesize – XST” button. Note that Xilinx displays all allowed options for the selected file in the project. For example, selecting the io.ucf file does not provide options like synthesis, etc. since it really is not a Verilog module.

Synthesis will take some time. If successful, you will see a green

check-mark Double-click “Generate Programming File”

to generate the bit-file You can expand the synthesis tab and look

at the synthesis report, warnings, critical path delay, etc.

Errors and warnings Heed them and you will learn as you go Ask labbies

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Adding SSD signal

Add extra output ssd Pulls all seven-segment

display limbs up for the decoder, so that you don’t see a faint glow

Same limbs will find use in core of your SS module UCF entries are handy

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UCF for complete design

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Generate programming file

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Programming the FPGA

Once the bit-stream is generated, we will configure the FPGA using the boundary-scan port Boundary-scan and JTAG are features used for

post-production test of ICs using very simple shift-register concepts and 4 I/O pins

The parallel-port connector lists these as TDI, TDO, TCLK, and TMS (test data in, …)

Can be used to configure FPGAs using the Adept software (icon below)

Programming the FPGA

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Programming the FPGA

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