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  2. Topic: AXI4-Lite Read/Write Transaction at Runtime

AXI4-Lite Read/Write Transaction at Runtime

Using Debug (ILA - Integrated Logic Analyzer) on AXI4-Lite Bus

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Scope AXI4-Lite Read/Write Transaction at Runtime

To understand how AXI4-Lite works, nothing is better than scoping it while it is running. In this section, you will use chipscope to scope the AXI4-Lite read and write transaction to your myled custom IP core when it is running on your board.

Step 1: Open LED Controller Project

Open Vivado tools menu, and click on Open Existing Projects. Navigate to myled project and open the project. Then open the block design as show in figure 1.

Figure 1. Open LED Controller Project
Figure 1. Open LED Controller Project

Step 2: Add Debug on AXI Bus of myled IP Core

Select the AXI Bus of myled IP Core. Then right click on the selected AXI bus, and select Debug in the drop down menu.

Figure 2. Mark DEBUG on the selected AXI bus.
Figure 2. Mark DEBUG on the selected AXI bus.

You should see the debug icon labeled on the marked AXI bus.

Figure 3. After the AXI bus is marked, you will see two bug marks in the block diagram.
Figure 3. After the AXI bus is marked, you will see two bug marks in the block diagram.

You can mark signal as debug in Verilog as well

If you want to scope an internal signal in your IP module, you can mark Debug in your Verilog code as well. In the codes below, you can also mark slv_reg0 with DEBUG property. Note that the KEEP property is usually marked together with DEBUG so that the synthesizer will not remove the signal during optimization.

//-- Number of Slave Registers 4
(* mark_debug = "true", keep = "true" *)
reg [C_S_AXI_DATA_WIDTH-1:0]    slv_reg0;
(* mark_debug = "true", keep = "true" *)
reg [C_S_AXI_DATA_WIDTH-1:0]    slv_reg1;
(* mark_debug = "true", keep = "true" *)
reg [C_S_AXI_DATA_WIDTH-1:0]    slv_reg2;
(* mark_debug = "true", keep = "true" *)
reg [C_S_AXI_DATA_WIDTH-1:0]    slv_reg3;

Step 3: Run Synthesis, Open Synthesized Design, and Add Logic Analyzer Core

First Run synthesis then select Set Up Debug in the Flow Navigator window. You’ll be promted to open up the synthesized design, click YES.

Figure 4. Open Synthesized Design and Select Set Up Debug
Figure 4. Open Synthesized Design and Select Set Up Debug

A Set Up Debug dialog will pop up for you to selected signals to scope and insert a logic analyzer core into your system. Click Next.

Figure 5. Set Up Debug Dialog
Figure 5. Set Up Debug Dialog

You will now see a dialog Nets to Debug window as shown in figure 6.

Note: If these Nets didn’t appear automatically in this window, click Find Nets to Add…. Then use drop down menu to change the filter property to MARK_DEBUG is true. You will now prompted with a dialog, select all signlas from there and click OK.

Figure 6.Nets to Debug Dialog
Figure 6.Nets to Debug Dialog

You will notice that the clock domain of signals system_i/ps7_0_axi_eriph_M00_AXI_BRESP and system_i/ps7_0_axi_eriph_M00_AXI_RRESP are undefined. This is because both signals are tied to ground (notice the GND in Driver Cell column) all the time. So, there is really no need to monitor those signals. Select them, right click and choose Remove Nets.

The the error message will go away and you can click Next to move on.

Figure 7. Remove signal BRESP as it is tied to GND all the time.
Figure 7. Remove signal BRESP as it is tied to GND all the time.

On ILA Core option page, you can select how many data the hardware should keep in its buffer. The depth of the sample data can be increase at the cost of more hardware resource consumption. In this lab, we can leave it at 1024.

For more details on the options, you can refer to UG908 Vivado Design Suite User Guide: Programming and Debugging for more information.

Figure 8. Configure ILA Core options.
Figure 8. Configure ILA Core options.

Now you will land on the summary page. Simply click Finish to close the Set Up Debug Dialog

Figure 9. Setup Debug Summary Page.
Figure 9. Setup Debug Summary Page.

Click on the Save button (or use key combination +s) to save the debug configuration to constraints file. You will see a few extra lines are added to the constraints file that details the connection of debugging signal and logic analyzer.

Figure 10. Save Debug Constraints.
Figure 10. Save Debug Constraints.

As you have added logic analyzer to the hardware project, you will need to run implementation and bitstream generation. You also need to export your hardware to your SDK project again so that it is up-to-date.

Step 4: Scope AXI4-Lite Read/Write Transaction at Run-time

In order to assure that you can scope the signals complete these 3 sub-steps before continuing:

  1. Make sure you generted the bitstream and exported the hardware including the bitstream.
  2. Lanch SDK (don’t close Vivado)
  3. Program FPGA from SDK and run the software on the board

Now, switch back to Vivado project, and click on Open Hardware Manager to open hardware manager. Then click Open Target and autmtically connect to your Blackboard.

Figure 11. Open Hardware Manager in Vivado
Figure 11. Open Hardware Manager in Vivado

In the Trigger Setup panel, click the Add Probes button to add probes.

Figure 12. Add probes to trigger setup.
Figure 12. Add probes to trigger setup.

In the pop up window, select signal system_i/ps7_0_axi_periph_M00_AXI_ARREADY.

Figure 13. Add ARREADY to trigger setup
Figure 13. Add ARREADY to trigger setup

Set the logic analyzer triggered by the time ARREADY signal is logic 1.

Figure 14. Set signal trigger value.
Figure 14. Set signal trigger value.

Click on the Play button to run trigger for this ILA core, and you will see the waveform window populated as soon as ARREADY jumps up to 1.

Figure 15. Run trigger.
Figure 15. Run trigger.

The following two figure shows the read/write transaction on AXI4-Lite bus using ILA debug core.

Figure 16. AXI4-Lite Read Transaction
Figure 16. AXI4-Lite Read Transaction
Figure 17. AXI4-Lite Write Transaction
Figure 17. AXI4-Lite Write Transaction