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Read Temperature Sensor Data From Xilinx FPGA Board Using FPGA Data Capture

This example shows you how to use FPGA Data Capture with existing HDL code to read FPGA internal signals. We start with an existing FPGA design that implements Xilinx XADC IP to read the on-chip temperature sensor data. The XADC IP exposes a dynamic reconfiguration port (DRP) interface for read and write internal registers. This FPGA design contains some simple logic that reads out the temperature sensor register from XADC IP. To obtain the temperature reading for further analysis, we use FPGA Data Capture feature to read the raw sensor data into MATLAB workspace. Then MATLAB converts the raw temperature data into meaningful Celsius number.

Requirements and Prerequisites

  • MATLAB

  • HDL Verifier

  • HDL Verifier Support Package for Xilinx FPGA Boards

  • Fixed-Point Designer

  • Xilinx® Vivado® Design Suite

  • ZedBoard or Xilinx Virtex-7 VC707 development board

Set Up FPGA Development Board

1. Make sure that the power switch remains OFF.

2. Connect the AC power cord to the power plug, and plug the power supply adapter cable into the FPGA development board.

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

4. Turn on the power switch on the FPGA board.

Prepare Example Resources

Set up a working folder and provide MATLAB with access to your FPGA design software.

1. Create a folder outside the scope of your MATLAB installation folder into which you can copy the example files. The folder must be writable. This example assumes that the folder is located at C:\MyTests.

2. Start MATLAB and set the current directory in MATLAB to the folder you just created. For example:

     cd C:\MyTests

3. To copy the example FPGA design files into your working directory, enter this MATLAB command:

     copyXilinxFPGAExampleFiles('xadc')

4. Set up Xilinx Vivado Design Suite. Here, we assume that the Xilinx Vivado executable is located in C:\Xilinx\Vivado\2018.2\bin\vivado.bat. If the location of your executable is different, use your path instead.

     hdlsetuptoolpath('ToolName','Xilinx Vivado','ToolPath','C:\Xilinx\Vivado\2018.2\bin\vivado.bat');

Generate FPGA Data Capture Components

At the MATLAB command prompt, enter:

     generateFPGADataCaptureIP

This command launches the FPGA Data Capture Component Generation application. This example monitors two signals from the existing HDL code for the temperature sensor system. The signals are a 16-bit "temperature", and 8-bit "counter". The "temperature" signal is the reading of register 0x00 from XADC, which stores the converted raw temperature sensor. It has 16 bits, but only the 12-bit most significant bits (MSB) are the raw temperature sensor reading. The last signal "counter" is an 8-bit free-running counter. To configure the data capture components to operate on these two signals, make the following changes:

1. Add one row to the Ports table by clicking the "Add" button once.

2. Name the first signal to "temperature", and the second signal to "counter".

3. Change the bit widths of the two signals to 16, and 8, respectively.

4. Set the FPGA vendor to Xilinx.

5. Ensure the selected language is Verilog.

6. Change the Sample depth to 1024. This is the number of samples of each signal that the data capture tool returns to MATLAB each time a trigger is detected.

7. Keep the Max trigger stages to 2. This is the maximum number of trigger stages that you can add during data capture to provide multiple trigger conditions.

The application settings will look as shown in the figure below:

Finally, click the "Generate" button to generate FPGA Data Capture component. A report shows the results of the generation.

Integrate the 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, we are going to connect the generated HDL IP with the temperature sensor output from XADC IP, and an 8-bit free-running counter.

If you are using ZedBoard, open the top.v file provided with this example. If you are using VC707, open the top_vc707.v file. Uncomment the following lines of code.

  datacapture u0 (
      .clk(clk),
      .clk_enable(1'b1),
      .ready_to_capture(),
      .temperature(do_out),
      .counter(counter[7:0]));

Save the file you modified, compile the modified FPGA design, and create an FPGA programming file.

If you are using ZedBoard, execute the following command

system('vivado -mode batch -source data_capture_xadc_zedboard.tcl &')

If you are using VC707, execute the following command

system('vivado -mode batch -source data_capture_xadc_vc707.tcl &')

The tcl scripts included in this example perform these steps:

1. Create a new Vivado 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 Vivado process successfully finishes before going to the next step. This process takes approximately 5 to 10 minutes.

Capture Data

First, go into the directory where the FPGA Data Capture component is generated.

     cd hdlsrc

Launch the FPGA Data Capture App. This app is customized for your data capture signals.

     launchDataCaptureApp

Click the "Capture Data" button to start data capture. This requests one buffer of captured data from the FPGA. The default is to capture immediately, without waiting for a trigger condition.

The captured data is saved into a struct, dataCaptureOut, in the MATLAB workspace. If you have DSP System Toolbox, the captured data is also displayed as signal waveforms in the Logic Analyzer.

The captured temperature sensor data is in raw format. The sensor data sheet gives the formula for converting it to Celsius units. Calculate and report the average temperature over all the samples returned.

     CelsiusTemp = (double(dataCaptureOut.temperature))/(2^4)*503.975/4096 - 273.15;
     sprintf('The FPGA Temperature is %fC\n',mean(CelsiusTemp))

Narrow the Scope of Data Capture Using Triggers

To capture data from the FPGA around a particular event, you can configure trigger conditions in the FPGA Data Capture App. For example, capture the temperature data only after a counter reaches a certain value.

Set Number of trigger stages to 1. In Trigger Stage 1, select "counter" from the trigger signal dropdown, and click "+" button to enable this trigger signal. Then set the corresponding trigger condition to 10. The trigger mode would automatically change to "On trigger". This tells the FPGA to wait for the trigger condition before capturing and returning data. The application settings will look like this:

Click Capture Data again. This time the data capture IP returns 1024 samples, captured when it detects the counter equals 10.

To capture data from the FPGA for specific bits in the trigger value, irrespective of other bits, you can configure the trigger condition with a bit-masked value.

For example, to capture the temperature data only when the seventh bit of the counter is 1, set the trigger condition to 0bX1XXXXXX as shown in the figure below:

Click Capture Data.

The data capture IP triggers to capture the temperature data for counter values in [64, 127] and [192, 255].

Capture Multiple Occurrences of an Event

To capture a recurring event from the FPGA, configure Number of capture windows in the FPGA Data Capture App.

For example, to capture the temperature data at eight different time slots, select the Number of capture windows to "8". The configuration will now look as shown in the figure below:

Click Capture Data. The data capture IP returns eight windows of 128 samples each, which amounts to a total sample depth of 1024.

     Window depth = Sample depth/Number of capture windows;

The result is seen in the Logic Analyzer as eight occurrences of the trigger, with the temperature logged for 128 samples each:

The signals "Capture Window" and "Trigger Position" indicates corresponding window number and trigger position respectively.

Capture Data in Multiple Trigger Stages

This scenario explains how to capture data by providing a sequence of trigger conditions in multiple trigger stages. For this, you must set the Number of trigger stages to a value more than 1 in the FPGA Data Capture App.

For example, to capture an temperature data when the counter value reaches from 0 to 5 in 5 clock cycles:

1. Set the Number of trigger stages to 2.

2. In the Trigger Stage 1, select "counter" from trigger signals and click "+" button to enable the trigger signal. Set the corresponding trigger condition value to 0.

3. In Trigger Stage 2, select "counter" from trigger signals and click "+" button to enable the trigger signal. Set the corresponding trigger condition value to 5. Enable the Trigger time out and set it to 5.

The application settings will look like this:

Click Capture Data. The data capture IP captures 1024 samples when it detects the trigger condition in Trigger stage 2 within 5 clock cycles, preceded by the trigger condition detected in Trigger Stage 1.