An XFP GUI allows the user to define up to four frequency domain vectors. The FrontPanel Subsystem Vivado IP Core stimulates our HLS Fast Fourier Transform (FFT) core to combine and convert these vectors into a time domain digital output signal. That digital output signal is then converted to analog with our SZG-DAC-AD9116 on the XEM8320-AU25P.

This sample paired with an Opal Kelly FPGA Development or Integration module provides a great starting template for those interested in DSP applications. The sample can be enhanced by additional DSP processing through additional user defined AMD-Xilinx’s HLS cores, or through AMD-Xilinx’s Filter, Modulation, Trig Functions, etc. DSP IP Cores.

• GitHub: Opal Kelly’s HLS Fast Fourier Transform (FFT) Core
  A synthesizable and scalable pipelined fixed-point Decimation-in-Frequency FFT and IFFT FPGA library for use with AMD-Xilinx’s High Level Synthesis (HLS).
  
• GitHub: FFT Signal Generator Sample
  A complete sample using the HLS FFT core above to create a signal generator. This sample targets the XEM8320 and the SZG-DAC-AD9116.
  

Users will be able to:

1. Create IPI Block Designer projects utilizing the FrontPanel Subsystem Vivado IP Core.
2. Use an XFP GUI with FrontPanel Scripting for GUI control of gateware.
3. Get introduced to a workflow that incorporates FrontPanel and AMD-Xilinx’s High Level Synthesis (HLS) components.

The end result of this tutorial is to use our prebuilt bitfile in-hardware to produce the following three-tone wave and capture it on an oscilloscope:

• Latest FFTSignalGenerator-vX.Y release files:
  – FFTSignalGenerator-vX.Y.bit
  – FFTSignalGenerator-vX.Y.lua
  – FFTSignalGenerator-vX.Y.xfp
• FrontPanel 5.2.12 or later
• XEM8320-AU25P
• SZG-DAC-AD9116 on Port A
• Oscilloscope
  Note: For best results, use an oscilloscope with 200 MHz bandwidth to best represent the SZG-DAC-AD9116’s full Nyquist bandwidth of 62.5MHz.

1. Connect a SZG-DAC-AD9116 to port A on the XEM8320-AU25P.
2. Power on the XEM8320-AU25P using a 12-volt supply.
3. Connect the XEM8320-AU25P to a PC using a USB-C cable.

1. Connect an oscilloscope probe to either SZG-DAC-AD9116 output’s center pin, and ground the signal on the outer SMA connector, if using a standard probe.
2. Set the oscilloscope to center 0 volts, with a vertical range of +/- ~1 volt.

1. Open FrontPanel 5.2.12 or later.
2. Click the Download FPGA Configuration button and select FFTSignalGenerator-vX.Y.bit.
3. Click the Load FrontPanel Profile button and select FFTSignalGenerator-vX.Y.xfp.
   Note: FFTSignalGenerator-vX.Y.lua needs to be in the same directory as FFTSignalGenerator-vX.Y.xfp.

1. Click Reset IFFT.
2. Enable Auto Scaling.
3. Enable bins 1, 2, and 3. Leave bin 4 disabled.
4. Set bin 1 to bin number 1, bin 2 to bin number 2, and bin 3 to bin number 18.
5. Use your mouse’s scroll wheel to set their corresponding dBFS values to -1, -7, and -28.
6. There should now be a three-tone sine wave displaying on the oscilloscope, as shown below.

We provide various build scripts for instructing Vitis HLS to build our FFT core, creating the Vivado project, configuring the required IP Cores, and constructing the IPI Block Design Project. The end result of this How-To is the construction of the following Vivado IPI Block Design project:

This design requires the following to build:

• Vitis HLS
  Notice: Our supported version is v2022.1. Versions outside of this are not guaranteed to be maintained.
• Vivado
  Notice: Our supported version is v2022.1. Versions outside of this are not guaranteed to be maintained.
• Vivado IP Cores’ Distribution v1.0.2 or later
• XEM8320-AU25P Board file v1.2 or later 
• Latest FFTSignalGenerator-vX.Y release Source Code (zip or tar.gz)

Windows

1. Follow How-To Install for the XEM8320-AU25P’s Board file v1.2 or later.
2. Follow Add IP Cores’ Distribution to Vivado for Vivado IP Cores’ Distribution v1.0.2 or later. The location you installed this Distribution to will be used in step 6.
3. Uncompress the sample’s release zip/tar.gz.
4. Open a command prompt and cd to the directory containing the sample’s Build folder.
   cd C:/pathToDownload/design-resources-FFTSignalGenerator-vX.Y/ExampleProjects/FFT_Sample/Build
   Note: PowerShell won’t work, Command Prompt must be used.
5. Run the settings64.bat file in the Vitis HLS and Vivado installation directories.
   path/to/vitis/2022.1/settings64.bat
path/to/vivado/2022.1/settings64.bat
6. Run the .bat file with the path to the Vivado IP Cores’ Distribution as an argument.
   windows_create_project.bat C:/pathToDownload/FrontPanel-Vivado-IP-Dist-vX.Y.Z

Linux

1. Follow How-To Install for the XEM8320-AU25P’s Board file v1.2 or later.
2. Follow Add IP Cores’ Distribution to Vivado for Vivado IP Cores’ Distribution v1.0.2 or later. The location you installed this Distribution to will be used in step 6.
3. Uncompress the sample’s release zip/tar.gz.
4. Open a terminal window and cd to the directory containing the sample’s Build folder.
   cd pathToDownload/design-resources-FFTSignalGenerator-vX.Y/ExampleProjects/FFT_Sample/Build
5. Run the settings64.sh files in the Vitis HLS and Vivado installation directories.
   source path/to/vitis/2022.1/settings64.sh
source path/to/vivado/2022.1/settings64.sh
6. Run the .sh file with the path to the Vivado IP Cores’ Distribution as an argument.
   linux_create_project.sh pathToDownload/FrontPanel-Vivado-IP-Dist-vX.Y.Z

We utilize the Behavioral Simulation features of the FrontPanel Subsystem Vivado IP Core to provide a simulation of the Signal Generator. The end result of this How-To is the creation of a simulation waveform for a two-tone wave:

1. Follow How-To Setup the Project
2. In Vivado, launch Flow>Run Simulation>Run Behavioral Simulation
3. Launch Run>Run All

1. Follow How-To Setup the Project
2. In Vivado, launch Flow>Generate Bitfile

Below we define terms and three important data flow stages for this sample:

• Vector Set – The 256 frequency domain vectors the FFT computes with.
• Load – The XFP GUI with FrontPanel Scripting communicates with the FrontPanel Subsystem Vivado IP Core generated FrontPanel HDL endpoints to store the Vector Set into the Frequency Domain BRAM. A custom RTL Slicer is used to distribute control signals throughout the design.
• Triggered Compute & Store – This action is triggered by the host when a change in the Vector Set occurs within the XFP GUI. After the computation has completed, the result is stored in the Time Domain BRAM.
• Continuous Output – A address generator provides a continuously incrementing address to the Time Domain BRAM to output the periodic time domain digital signal to the SZG-DAC-AD9116. The SZG-DAC block is based heavily on the SZG-DAC signal generator.

The user interface shown above has the following components to control the behavior of the FFT signal generator:

• Bin Number – This selects a frequency bin number in the FFT to activate, from 0 to 127.
• dBFS – DeciBel Full Scale. 0 = full power, 120 = nearly off.
  Note: You must use your scroll wheel to input into this entry
• Enable – If unchecked, disables the bin. Also discludes the dBFS value from any Auto Scaling calculations.
• Frequency (kHz) – The frequency of the specified Bin Number.
• Enable Auto Scaling – If enabled, will prevent the sum of all the bin values (calculated from dBFS) from going over the maximum. This will prevent clipping. For example, if two bins were enabled with a dBFS of zero, the Lua script will halve the components to the selected bins and the output signal from the SZG-DAC will not be clipping.
• Reset IFFT – Resets the design.

A limitation of the provided XFP and Lua script is the lack of the ability to set the phase of the frequency domain vectors. This involves incorporating the complex component of the frequency bins. In gateware, the functionality to do this is present, but is not implemented in the XFP and Lua script.

Our supported releases for the FFT Signal Generator sample are located on GitHub at:
opalkelly-opensource/design-resources Releases

• Initial Creation
• Bitfile generated using the following tool versions:
  Vivado v2022.1
  Vitis HLS v2022.1
  Vivado IP Cores’ Distribution v1.0.2
  XEM8320-AU25P Board file v1.2