Creating Pynq images for custom boards.

In this blog we already talk about Pynq and how it can help us to develop some applications in a easy way. Obviously, Pynq has its limitations but it still being a powerful tool with we can develop projects in a few minutes. Pynq is Jupyter-notebook based, and includes the corresponding libraries to communicate our Python notebook with the PS and their AXI4 interfaces. That mix between a SoC and Python can be an excellent DSP tool, since Python has many DSP libraries like the Signal package of Scipy, but it is not capable to execute algorithm in real time. on the other side, compute the constants inside the FPGA can be very tedious, but the FPGA is perfect to execute algorithms in real time, so the mix of both will be capable of compute the constants of the algorithm and also execute it in real time.

Unfortunately, Pynq images are only available for a few number of boards. In this blog we used Pynq with the Ultra96 of Avnet, and the Pynq-Z2 of TUL, but neither of this boards are designed or have interfaces for signal processing. Luckily, Pynq is based on Petalinux, so its possible to compile a Pynq image for any board based on Zynq. In this post we will create a Pynq Image for Digilent’s Eclypse Z7, that with its SYZYGY interfaces is an excellent choice for DSP.

First of all we need to create a hardware definition for our Petalinux distribution. This hardware definition is only for the startup of Petalinux, because later, when we will need to add new IPs or peripherals we will reload the hardware design, in Pynq words, we can change the overlay, inside the Pynq environment. For the Eclypse Z7 board we will define only the Zynq processing system and the IP for the management of the IOs through an AXI GPIO IP. The block design will show like the next.

Once the block design is complete, we have to generate the bitstream and then export the hardware. For this project I am using Vivado 2019.1 because I tried to make the same with Vivado 2020.1 but it doesn’t works well, and the differences of both versions of Vivado for 7z020 are not relevant.

Now we have to clone the git repository of Pynq. The entire repository has all the releases of Pynq, and the head of the repository is in the newer version, that is v2.6.1. Since the version of Vivado we are using is not the last, we need to checkout the Pynq files to the correct version. According Pynq webpage, the release that works with Vivado and petalinux 2019.1 is v2.5, so we need to execute the next line inside the Pynq repository.

pablo@ubuntu1804vm2:~/git/PYNQ$ git checkout v2.5.1

Once we are in the correct tag of Pynq, we need to install and configure our host machine to build a Pynq Image. Since this step will install in our system different packages only used for Pynq built, I recommend you work from a virtual machine. To run this step, we have to execute the script which is located on /sdbuild folder.

pablo@ubuntu1804vm2:~/git/PYNQ/sdbuild/scripts$ source 

Now, we can start the process. First of all, inside the Pynq folder, in the boards folder, we need to create a new board. For this project I will create the folder eclypse-z7. Inside this folder we have to create the .spec file where we will configure the architecture and the packages we will add to the distribution. Also we can add the bsp file if we have it. In this case, I don’t have a bsp for the Eclypse Z7 board, so I will add the .hdf file to the folder, and the BSP line will remain empty.

ARCH_eclypse-z7 := arm
BSP_eclypse-z7 :=

STAGE4_PACKAGES_eclypse-z7 := pynq ethernet

The .hdf file has to be added to petalinux_bsp/hardware_project folder. The directory tree will looks like the next.

pablo@ubuntu1804vm2:~/git/PYNQ$ tree -L 3 ./boards/eclypse-z7/
├── eclypse-z7.spec
└── petalinux_bsp
    └── hardware_project
        └── eclypse_base_bd_wrapper.hdf

To run the Pynq image built, we have to add to the PATH all the tools that Pynq we will need to create the image. I have created the file that I have to run before the Pynq built. That file contains the next commands.

export PATH="/opt/crosstool-ng/bin:/opt/qemu/bin:$PATH"
source /tools/Xilinx/Vivado/2019.1/
source /tools/Xilinx/SDK/2019.1/
source ~/petalinux/
petalinux-util --webtalk off

When is executed, the output will be the next.

pablo@ubuntu1804vm2:~/git/PYNQ$ source 
PetaLinux environment set to '/home/pablo/petalinux'
WARNING: /bin/sh is not bash! 
bash is PetaLinux recommended shell. Please set your default shell to bash.
INFO: Checking free disk space
INFO: Checking installed tools
INFO: Checking installed development libraries
INFO: Checking network and other services
WARNING: No tftp server found - please refer to "PetaLinux SDK Installation Guide" for its impact and solution
INFO: Turn off webtalk feature!

Finally, we can execute the make for the corresponding board, and wait a couple of hours to the image has been created.

pablo@ubuntu1804vm2:~/git/PYNQ/sdbuild$ make BOARD=eclypse-z7

Once the process has finished, in the output folder will be available the new Pynq image for the Eclypse Z7 board.

In this post I have used the Digilent’s Eclypse Z7 board, but the process is the same for any board based on Xilinx Zynq7000 or Zynq MPSOC, so you can try to generate your own Pynq image.

Due to the summer holidays, this is the last post of the season, the next post will be available on August 30th. For the next season I have some ideas, including some gifts for the readers! Keep safe and thanks for read!

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