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Stream Audio Signal from Intel FPGA Board Using Ready-to-Capture Signal

This example shows how to use a ready-to-capture signal in an FPGA data capture with existing HDL code to read FPGA streaming signals. This example starts with an existing FPGA design that implements an on-chip analog-to-digital converter (ADC) to sample an audio signal. The ADC intellectual property (IP) exposes an Avalon® memory-mapped (MM) slave interface for control and an Avalon streaming interface for data output. The existing example contains a simple Avalon MM master to start the ADC. Use FPGA data capture to collect the ADC output data from the Avalon streaming interface and stream the data to the MATLAB® workspace.

The ready_to_capture signal is output from the FPGA data capture HDL IP. This output captures continuous data provided that you places a first-in first-out (FIFO) in front of the FPGA data capture HDL IP and check the ready_to_capture signal before streaming data to the data capture IP. You might also need to check that the FIFO is not empty. This figure illustrates the continuous data capture workflow.

The audio data from the Avalon streaming interface is written into a FIFO, and the FIFO is read when the ready_to_capture signal is asserted. To avoid data overflow, the FIFO must be large enough to capture data when ready_to_capture is deasserted. In this example, the FIFO depth is configured to 16 k and the audio sampling frequency is 50 kHz.

Requirements and Prerequisites

Set Up FPGA Development Board

1. Confirm that the power switch is off.

2. Connect the JTAG download cable between the FPGA development board and the host computer.

3. (Optional) Connect the line-in port of the FPGA board with an audio source, such as your cellphone, via 3.5 mm audio cable. If you skip this step, the captured data will be random noises.

Prepare Example Resources

Set up the Intel Quartus. This example assumes that the Intel Quartus executable is located in the file C:\altera\18.0\quartus\bin\quartus.exe. If the location of your executable is different, use your path instead.

  hdlsetuptoolpath('ToolName','Altera Quartus II', ...

Generate FPGA Data Capture Components

Launch the FPGA Data Capture Component Generator tool by executing this command in MATLAB.


This example monitors one signal from the existing HDL code for the audio system. The signal is a 12 bit adc_out. The adc_out signal is the digital samples of the audio line-in signal. To configure the data capture components to operate on this signal, follow these steps.

1. Set FPGA vendor to Altera.

2. Set Generated IP language to Verilog.

3. Rename the signal to adc_out in the ports table.

4. Change the bit width of the signal to 12.

5. Set Sample depth to 8192. This value is the number of samples of each signal that the data capture tool returns to MATLAB each time a trigger is detected.

This figure shows these tool settings.

To generate the FPGA data capture component, click Generate. A report shows the results of the generation.

Integrate FPGA Data Capture HDL IP

You must include the generated HDL IP core into the example FPGA design. You can copy the module instance code from the generated report. In this example, connect the generated HDL IP with the ADC output via a FIFO.

Open the readyToCapture_top.v file provided with this example. Uncomment this code.

datacapture1 u0(

Save readyToCapture_top.v, compile the modified FPGA design, and create an FPGA programming file by using the following Tcl script.

  system('quartus_sh -t readyToCapture_deca_max10.tcl &')

The Tcl scripts that are included in this example perform these steps.

1. Create a new Quartus project.

2. Add example HDL files and the generated FPGA data capture HDL files to the project.

3. Compile the design.

4. Program the FPGA.

Wait until the Quartus process successfully finishes before going to the next step. This process takes approximately 5 to 10 minutes.

Capture Data

Navigate to the directory where the FPGA data capture component is generated.

  cd hdlsrc

You must set the capture mode to Immediate to use a ready-to-capture signal in an FPGA data capture. To capture data in the immediate mode, follow these steps.

1. Create an FPGA data capture System object™ and configure these properties.

DataCaptureObj = datacapture1;
DataCaptureObj.TriggerPosition = 0;
DataCaptureObj.NumCaptureWindows = 1;

2. Capture FPGA data continuously. In this example, capture NumberOfSampledepth snapshots of data. You can modify the NumberOfSampledepth value as needed.

NumberOfSampledepth = 10;
Sample_depth = 8192;
adc_out =  int16(zeros(NumberOfSampledepth*Sample_depth, 1));
for i = 1:NumberOfSampledepth
   [~,~,adc_out(i*Sample_depth-(Sample_depth-1):i*Sample_depth)] = step(DataCaptureObj);

3. Save the captured audio data by writing the captured data to .wav format. Process or replay the captured data at a later time.


4. View the captured data in the Logic Analyzer tool. The Logic Analyzer tool can take a few seconds to load the captured snapshots of data.

scope = dsp.LogicAnalyzer('NumInputPorts',1, ...
                          'DisplayChannelFormat','Analog', ...
tags = getDisplayChannelTags(scope);

This figure shows 8 k samples of audio data in the Logic Analyzer tool.

See Also



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