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Accelerating Communications System Simulation Using FPGA-in-the-Loop

This example uses FPGA-in-the-Loop (FIL) simulation to accelerate part of a communications system. The application uses the Viterbi Algorithm to decode a convolutional encoded random stream that is BPSK modulated, sent through an AWGN channel, and then demodulated. Using a sample-by-sample approach leads to a modest speedup over normal Simulink® simulation, while using the "Process as Frames" option leads to further speedup.

This example uses the Communications Toolbox™ in conjunction with HDL Coder™ and HDL Verifier™ to show a design workflow for accelerating simulation using FPGA-in-the-loop.

Requirements and Prerequisites

Tools required to run this example:

  • FPGA design software

  • One of the supported FPGA development boards. For supported hardware, see Supported FPGA Devices for FPGA Verification.

  • For connection using Ethernet: Gigabit Ethernet Adapter installed on host computer, Gigabit Ethernet crossover cable

  • For connection using JTAG: USB Blaster I or II cable and driver for Intel FPGA boards. Digilent® JTAG cable and driver for Xilinx FPGA boards.

  • For connection using PCI Express®: FPGA board installed into PCI Express slot of host computer.

Requirements: MATLAB® and FPGA design software can either be locally installed on your computer or on a network accessible device. If you use software from the network you will need a second network adapter installed in your computer to provide a private network to the FPGA development board. Consult the hardware and networking guides for your computer to learn how to install the network adapter.

1. Open and Execute the Simulink Model

Open the model. Due to the large quantity of data to process, the simulation takes approximately 9 seconds without FIL. We will improve the simulation speed in the following steps by using a FPGA-in-the-Loop.

2. Generate HDL Code

This step requires HDL Coder. If you do not have HDL Coder, you can use pre-generated HDL files in the current directory.

If you are going to use these copied files, go directly to step 3.

Generate HDL code for the Viterbi block subsystem by performing these steps:

a. Right click on the existing FIL block labeled viterbi_block1. Click on Delete to remove this block for code generation.

b. In the Modeling tab, click Model Settings.

d. Click on the HDL Code Generation pane and make sure the hdlcoderviterbi_for_fil/viterbi_block is selected.

e. Click Generate.

Alternatively, you can generate HDL code by entering the following command at the MATLAB prompt:


3. Set FPGA Design Software Environment

Before using FPGA-in-the-Loop, make sure your system environment is set up properly for accessing FPGA design software. You can use the function hdlsetuptoolpath to add FPGA design software to the system path for the current MATLAB session.

4. Run FPGA-in-the-Loop Wizard

To launch the FIL Wizard, enter the following command at the MATLAB prompt:


4.1 Hardware Options

Select a board from the board list. Click Next to continue.

4.2 Source Files

a. Add all the previously generated HDL source files for the Viterbi Block subsystem.

b. Select the file viterbi_block.vhd as the Top-level file. You may need to make the FPGA-in-the-Loop Wizard window wider in order to see these options.

c. Notice that the viterbi_block has been entered for you as the default top-level module name. Click Next to continue.

4.3 DUT I/O Ports

Observe that the ports of the top-level module have been correctly identified. Click Next to continue.

4.4 Build Options

a. Select an output folder.

b. Click Build to build the FIL block and programming file.

During the build process, the following actions occur:

  • A FIL block named viterbi_block is generated in a new model.

  • After new model generation, the FIL Wizard opens a command window where the FPGA design software performs synthesis, mapping, place-and-route, timing analysis, and FPGA programming file generation. For this block, these steps take about 20 minutes.

When the FPGA design software process is finished, a message in the command window lets you know you can close the window.

5. Open and Complete the Simulink Model for FIL

a. Open the hdlcoderviterbi_for_fil.mdl

b. Copy into it the previously generated FIL block and connect it either in parallel to or in place of the viterbi_block. Note that the original block has the inputs on the right. To make the FIL block have its inputs on the right, right-click the block, and then select Format > Flip Block.

6. Configure FIL Block

a. Double-click the FIL block in the model to open the block mask.

b. Click Load.

c. Click OK to close the block mask.

7. Run FIL Simulation

Run the simulation for 20480 seconds and observe the performance.

FrameSize = 1;
fs1 = toc

You can try setting the frame size to a larger number. For this example, the frame size is set to 1024 bytes.

FrameSize = 1024;
fs2 = toc

In our tests, the time to simulate was around 16 seconds when FrameSize = 1, which is about the same as simulating in Simulink without FIL, but the simulation time was decreased to around 12 seconds when the frame size was increased to 1024 using a Xilinx Spartan-6 SP605 board. This particular board and system gives an overall speedup of around 1.7 times faster, but other boards and communications system may be even faster.

speedup = fs1 / fs2

By removing the Simulink block version and only simulating the FIL version, and by adding more blocks to the FIL part of the design and removing the Simulink scopes and displays as much as possible, even greater speedups are possible.

This concludes the Accelerating Communications System Simulation Using FPGA-In-the-Loop example.