By Adam Taylor
Being able to see internal software variables in our Zynq-based embedded systems in real time is extremely useful during system bring-up and for debugging. I often use an RS-232 terminal during commissioning to report important information like register values from my designs and have often demonstrated that technique in previous blog posts. Information about variable values in a running system provides a measure of reassurance that the design is functioning as intended and, as we progress though the engineering lifecycle, provides verification that the system is continuing to work properly. In many cases we will develop custom test software that reports the status of key variables and processes to help prove that the design functions as intended.
This approach works well and has for decades—since the earliest days of embedded design. However, a better solution for Zynq-based systems that allows us to read the contents of the processor memory and extract the information we need without impacting the target’s operation and without the need to add a single line of code to the running target now presents itself. It’s called μC/Probe and it’s from Micrium, the same company that has long offered the µC/OS RTOS for a wide variety of processors including the Xilinx Zynq SoC and Zynq UltraScale+ MPSoC.
Micrium’s μC/Probe tool allows us to create custom graphical user interfaces that display the memory contents of interest in our systems designs. With this capability, we can create a virtual dashboard that provides control and monitoring of key system parameters and we can do this very simply by dragging and dropping indicator, display, and control components onto the dashboard and associating them with variables in the target memory. In this manner it is possible to both read and write memory locations using the dashboard.
When it comes to using Micrium’s μC/Probe tool with our Zynq solution, we have choices regarding interfacing:
- Use a Segger J Link JTAG Pod. In this case, the target system requires no additional code unless we wish to use an advanced μC/Probe feature such as an oscilloscope.
- Use RS-232, USB, or TCP/IP. In this case we do not need to use JTAG. However we do need to add some code to the target embedded system. Micrium supplies sample code for us to use.
For this first example, I am going to use a Segger J Link JTAG pod to create a simple example and demonstrate the capabilities. However, the second interface option proves useful for Zynq-based boards that lack a separate JTAG header and instead use a USB-to-JTAG device or if you do not have a J Link probe. We will look at using Micrium’s μC/Probe tool with the second interface option in a later blog.
Of course, the first thing we need to do is create a test application and determine the parameters to observe. The Zynq SoC’s XADC is perfect for this because it provides quantized values of the device temperature and voltage rails. These are ideal parameters to monitor during an embedded system’s test, qualification, and validation so we will use these parameters in this blog.
The test application example will merely read these values in a continuous loop. That’s a very simple program to write (see MicroZed Chronicles 7 and 8 for more information on how to do this). To understand the variables that we can monitor or interact with using μC/Probe, we need to understand that the tool reads in and parses the ELF produced by SDK to get pointers to the memory values of interest. To ensure that the ELF can be properly read in and parsed by μC/Probe, the ELF needs to contain debugging data in the DWARF format. That means that within SDK, we need to set the compile option –gdwarf-2 to ensure that we use the appropriate version of DWARF. Failure to use this switch will result in μC/Probe being unable to read and parse the generated ELF.
We set this compile switch in the C/C++ build settings for the application, as shown below:
Setting the correct DWARF information in Xilinx SDK
With the ELF file properly created, I made a bootable SD card image of the application and powered on the MicroZed. To access the memory, I connected the Segger J Link, which uses a Xilinx adaptor cable to mate with the MicroZed board’s JTAG connector.
MicroZed with the Segger J Link
All I needed to do now was to create the virtual dashboard. Within μC/Probe, I loaded the ELF by clicking on the ELF button in the symbol browser. Once loaded, we can see a list of all the symbols that can be used on μC/Probe’s virtual dashboard.
ELF loaded, and available symbols displayed
For this example, which is monitoring Zynq SoC’s XADC internal signals including device temperature and power, I added six Numeric Indicators and one Angular Gauge Quadrant. Adding graphical elements to the data screen is very simple. All you need to do this find the display element you desire in the toolbox, drag onto the data screen, and drop it in place.
Adding a graphical element to the display
To display information from the running Zynq SoC on μC/Probe’s Numeric Indicators and on the Gauge, I needed to associate each indicator and gauge with a variable in memory. We use the Symbol viewer to do this. Select the variable you want and drag it onto the display indicator as shown below.
Associating a variable with a display element
If you need to scale the display to use the full variable range or otherwise customize it, hold the mouse over the appropriate display element and select the properties editor icon on the right. The properties editor lets you scale the range, enter a simple transfer function, or increase the number of decimal places if desired.
Formatting a Display Element
Once I’d associated all the Numeric Indicators and the Gauge with appropriate variables but before I could run the project and watch the XADC values in real time, one final thing remained: I needed to inform the project how I wished to communicate with the target and select the target processor. For this example, I used Segger’s J Link probe.
Configuring the communication with the target
With this complete. I clicked “run” and captured the following video of the XADC data being captured and displayed by μC/Probe.
All of this was pretty simple and very easy to do. Of course, this short has just scratched the surface of the capabilities of Micrium’s μC/Probe tool. It is possible to implement advanced features such as oscilloscopes, bridges to Microsoft Excel, and communication with the target using terminal windows or more advanced interfaces like USB. In the next blog we will look at how we can use some of these advanced features to create a more in-depth and complex virtual dashboard.
I think I am going to be using Micrium’s μC/Probe tool in many blogs going forward where I want to interact with the Zynq as well.
You can find the example source code on the GitHub.
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November 15, 2017 at 12:08AM