Xilinx ISE Tutorial DKOP

Ajay Sharma – [email protected] www.dkoplabs.com Page 1

Xilinx Tools Tutorial -1

Using ISE for FPGA Implementation

• ISE v- 12.1

• FPGA Kit- Digilent Nexys2 (Spartan 3E ) board

• Design of half adder using dataflow modeling.

• Syntax Check

• Create test fixture using tool’s wizard

• Simulation of half adder

• Design of full adder using gate level modeling (instantiation of half adders).

•


DESIGN ENTRY

1. Run ISE, the Integrated Simulation Environment:

Double click the icon .

Or Start Menu � All Programs � Xilinx ISE Design Suite 12.1 � ISE Design Tools � Project Navigator.

Take your time and make yourself familiar with the interface.

Before starting to code for Synthesis the designer must know the concept of RTL and should

have gone through the Synthesis tool’s reference manual.

Though while doing beginner exercises for practice you might not have read the Synthesis and

that is OK (you may skip & it may be acceptable while doing simulations) but later as you will

go forward to code for synthesis or working on a real project you MUST know the concept of

Synthesis and must have gone through the Synthesis Manual.


2. Make New Project:

Click ‘New project’. A new project is made once for a new design (the design may have many leaf cells in the

hierarchy these cells are created within the existing project). To open and work with existing design, use ‘open

project’. Though, mostly, ISE Project navigator keeps last active project on startup.

The project is named ‘adder_sample’. It is located in the directory ‘E:\xilinx_proj’.

It is suggested that the designer always organize the directory structure and must know where

the design project has been created.

It is important how the project is organized. It is strongly recommended that the naming is done

sensibly. As a convention, name the Verilog file same as the module name and the variations of

similar module be name with a variation. For instance, if I am to design a 4 bit ripple carry

adder, I may name the adder as ‘adder_4bit_ripl.v’, its module name as ‘adder_4bit_ripl’.


Choose the Kit’s FPGA available:

After filling the FPGA device form � ‘Next’.

Typically, a mixed approach is used in designing. In the first step the top design is broken down

to the leaf cells, this is called ‘top down’ approach. Now the design is built/coded from the very

leaf/child cell (lowest level). Once all the lowest level leaf/child cells are created the upper level

cells are created using these lowest level leaf/child cells. In this way the top level design is

reached.

It is just like building a house. First an architecture is drafted on a paper. Then basic building

blocks like concrete and bricks etc are used to create rooms and bit by bit a house(top level) is


Summary:

See the project summary, if everything looks OK, � ‘Finish’. Otherwise go back to select correct options and

finally chose ‘Finish’.

Tool Control:

Figure below shows two important aspects of the tool.


3. Adding Files:

Now new files can be created or existing files can be added to the project.

In the Xilinx ‘Tool Bar’ select ‘Project’ � ‘New Source’

In ‘New Source Wizard’ � ‘Verilog Module’ (in the list on the LHS) � Give appropriate name for the verilog

module ` half_adder_dfl’ (half adder using dataflow modeling) � ‘Next’ :

Insert the port names:


Check that the Summary details are correct. Go back to change until sure that everything is OK.


Once a Verilog module is created using a wizard, the ‘Project Navigator will look like as shown below:

An outline of module with input output ports just specified is created. Now, body part can be coded. Also,

Notice (in figure above) that the design is added as a “top module” under the FPGA device chip in the ‘Design’

section. And since the design is top module and is selected, ‘processes’ section will show all the available

options for the module.

Remember, only Top Module can be implemented on the FPGA.


Half adder’s body has been coded by using datflow level modeling as shown below:

4. Check Syntax:

The code should be checked for any syntax errors.

Check the Console to see if succeeded:


There is an error, compiler cannot find inb, it should be in_b instead.

Make changes and Check syntax again:

Code is OK Syntactically!


SIMULATION:

5. Run the Simulation:

Create New Source for the project but this time the new source will be ‘Verilog Test Fixture’ and click ‘Next’:

Associate the source with the appropriate module and click ‘Next’:


See the project summary, if everything looks OK, � ‘Finish’. Otherwise go back to select correct options and

finally chose ‘Finish’.


Insert the test bench stimulus code:

Change the ‘View’ in Design section from ‘Implementation’ to ‘Simulation’.

Select the test bench file and double click ‘Simulate Behavioral Model’ in the ‘Process’ section:


This will flush information in the Console section and will finally open the ‘ISim’, the Integrated Simulator.

Analyze the simulation results in the waveform window.

Waveform Window


Make yourself familiar with the Simulator.


Full adder using half adder instances:

Now, a full adder will be created by using instances of the half adders just created. This will be gate level

modeling. Also, instead of using the wizard’s input/output, the Inputs and outputs will be written manually in

the file.

Add New Source:

‘Xilinx Tool Bar’ � ‘Project’ � ‘New Source’

OR, RtClick Chip � ‘New Source’


Next Window will be skipped:

Verify the Summary.

If some changes required go back otherwise Click ‘Finish’.

This time, there are no ports:

Complete the design by writing the code for the full adder:


In the design full adder is named ‘full_adder_gl’. It is easy to understand later without opening the .v file that it

is a full adder with gate level modeling.

Following full adder uses place instantiation. Named instantiation is strongly recommended.

Recommended coding style:


Make sure that the top module is the correct module that supposed to be top. Since half adders (half_adder_dfl)

combine to make a full adder (full_adder_gl) higher level, full adder must be the top module till this design. If

the full adder is further used to make a 4 bit ripple carry adder, the 4 bit carry adder would be the top module

then.

Check Syntax:

Make sure the correct source/module is selected and run the syntax check.

Check to see any syntax errors.

Correct the code until it is syntactically clean. Run the check until successful.


Run the Simulation:

Make a test bench code for the full adder and run the simulation. Make sure that the test bench is associated

with the correct module (right click the module full adder and then add the new source). Give test fixture a

name ‘full_adder_gl_tw1’.

You may insert the stimulus in the test fixture file as:

#100 a=0; b=1;

#100 a=1; b=0;

#100 a=1; b=1;

Simulation Results:

Check to see the simulation results similar to the one shown:


4 Bit Ripple Carry Adder:

Now it is time to design a ripple carry adder using 4 instances of full adders. Now, the 4 bit RCA will be the top

module.

This time, there will be a slight change in the Source creation. Although the RCA could have been made using

the same ‘New Source’. This time instead of ‘New Source’ an existing source will be added.

Create a .v file, ‘adder_4bit_rca.v’ using the text editor as you would in the tool. This file must exist before

proceeding further as it has to be browsed and added. So, place this file preferably in the working directory

that is, where the project is (eg. "E:/xilinx_proj/adder_sample/”).

Add Source:

Project � ‘Add Source’



The code is:

module adder_4bit_rca ( S,CO,A,B,CI); output [3:0] S; output CO; input [3:0] A,B; input CI; wire wc1, wc2, wc3; //Instantiations full_adder_gl fa0(.s(S[0]),.co(wc1) .ci(CI),.b(B[0]),.a(A[0])); full_adder_gl fa1(.s(S[1]),.co(wc2) .ci(wc1),.b(B[1]),.a(A[1])); full_adder_gl fa2(.s(S[2]),.co(wc3) .ci(wc2),.b(B[2]),.a(A[2])); full_adder_gl fa3(.s(S[3]),.co(CO) .ci(wc3),.b(B[3]),.a(A[3])); endmodule

Run ‘Check Syntax’ and fix the code until syntactically clean.

Recommended coding style:


Now the Hierarchy looks something like this:

Look at the hierarchy and understand it.

Run the Simulation:

Now make a test bench and rerun the simulation.

Sample test bench stimulus:


Results:

The simulation seems correct.


SYNTHESIS

For synthesis and rest of the flow ‘Implementation’ tab must be selected and only the top module is

synthesized. Selecting the top module in ‘Implementation’ tab will bring the implement flow options.

6. User Constraint:


This may take a while and opens ‘PlanAhead’ . Close the welcome screen and select ‘NO’ when asked for

updates.

From the I/O ports section select the ports one by one and fill in the site field (refer the FPGA board manual for

sites)


For Nexys 2 FPGA kit reference manual the locations filled in the port properties.

Make sure to save the plan. After save, the design can be synthesized. PlanAhead may be closed after saving if

not required.


Go back to the Project Navigator Window aka ISE.

Constraint file is .ucf file. After creating and saving the port plan in PlanAhead the file ‘adder_4bit_rca.ucf’

should be added and associated to the project files automatically. Verify that ‘adder_4bit_rca.ucf’ is added

under hierarchy in the ‘Design’ Section.

7. Synthesis:

The RTL can be synthesized now. Xilinx Synthesis Tool (XST) will be used for the synthesis.

Double Click ‘Synthesize XST’ to synthesize the design.


View RTL Schematic:

Double Click ‘View RTL Schematic’,

Double Click inside grey box to see the details (go further down the hierarchy).

RTL Schematic shows the resulting logic blocks and the connections between them.


View Technology Schematic:

Double Click ‘View Technology Schematic’,

The Technology schematic shows what exactly is going to be implemented on the FPGA.

View Summary and Reports:



Implementation:

Double Click Implement Design.

Once Completed, Implement Design’ will have a tick mark and this can be checked in the console as well.


Generate Programming File:

Right Click ‘Generate Programming File’ �



SUMMARY

ISE WINDOW: 1. Design Entry (Implementation mode):

a) New Project (only once every new project) ‘Project’ � ‘New Source’�’Verilog Module’ � give name �’Next’ � ‘Next’ �’Finish’.

b) Design Entry using Verilog (Verilog module) – DU (Design Unit) Write the verilog code for the design and save.

c) Syntax Check: SOURCE: Select correct file. PROCESS: Synthesize XST – Double Click ‘Check Syntax’.

2. Simulation (Behavioral Simulation mode): a) TB (Test bench) for the DU.

‘Project’ � ‘New Source’�’Verilog Test Fixture’ � give name �’Next’ � ‘Next’ �’Finish’. b) Edit the test fixture file by adding the appropriate stimulus. SOURCE: Select correct file. PROCESS: Xilinx ISE Simulator – Double Click ‘Simulate Behavioral Model ‘.

3. Assign FPGA component locations to the pins in DU(Implementation mode): SOURCE: Select the top module. PROCESS: ‘User Constraints’ – Double Click ‘Floor Plan IO – Pre-Synthesis

IMPACT WINDOW:

Assign appropriate locations to the pins in module and save. Go back to the ISE WINDOW.

ISE WINDOW: 4. Synthesis (Implementation mode):

SOURCE: Select the top module. PROCESS: Double Click ‘Synthesize XST’.

5. Implementation-translate, map, place & route (Implementation mode):

PROCESS: Double Click ‘Implement Design’.

6. Generate Program File (Implementation mode): ***Skip step 6. a) if programming on-board PROM. a) Right Click ‘Generate Programming File’ � ‘Properties’ � Category=’Startup Options’ � FPGA Start-Up Clock = ‘JTAG Clock’ � ‘OK’. b) Double Click ‘Generate Programming File’.

7. Programming the FPGA using Adept: a) Connect the FPGA kit with the PC via an appropriate USB connector. b) Switch the FPGA kit ‘ON’ (Red(Power) LED will glow). c) Window’s Start Button � ‘All Programs’ � ‘Digilent’ � ‘Adept’ � ‘Adept’.

ADEPT WINDOW: If the FPGA kit is powered ON, connected to the PC and the Digilent’s USB cable drivers are installed the Adept programmer window will auto recognize the connected FPGA kit and will show digilent’s device name (such as Nexsys2 or Basys2) under ‘Connect:’.


Also, the programming options will be available for: 1. FPGA. 2. PROM. For FPGA: (make sure the jumper is at USB/PC ) (The programming information will be lost at power ‘OFF’ and the FPGA has to be re-programmed at every power ‘ON’ and ‘OFF’ so, it is a volatile programming. To retain the programming information so that it is auto-loaded at every start-up, choose to program the on-board PROM)

a) Click ‘Browse’ (the one next to FPGA tab) � locate the bit file generated by ISE (will have same name as the top module and will be located in the project directory). If there is a ‘.bit’ at the location it will show.

b) Select the bit file � Click ‘Open’ � ‘Program’ (the one next to FPGA section).

c) Adept will report Program Successful.

For PROM: (make sure the jumper is at PROM/ROM)

(The programming information is retained and is auto-loaded at every start-up)

a) Click ‘Browse’ (the one next to PROM tab) � locate the bit file generated by ISE (will have same name as the top module and will be located in the project directory). If there is a ‘.bit’ at the location it will show.

b) Select the bit file � Click ‘Open’ � ‘Program’ (the one next to PROM section).

c) Adept will report Program Successful.

FPGA KIT: a) Check that a yellow ‘LED’ on the FPGA kit, glows. This indicates the FPGA has been programmed. b) Analyze/Observe the working of the design DU.

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Xilinx ISE Tutorial DKOP

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