Petalinux with Ethernet on the MYIR MYC-CZU3EG

One of my favourite FPGA development boards is the MYC-CZU3EG by MYIR. It is a compact module with a Xilinx Zynq UltraScale+ ZU3EG (now also available with ZU4EV and ZU5EV)

For development purposes there is a carrier board that offers a range of peripherals to experiment with, like USB, PMOD, Ethernet, SATA, FMC connector, etc. Not shown in the picture but the module is covered by a fan to be able to use it at high power.

I have built Linux with Petalinux tools for this board and others but actually few times I did it enabling and using the Ethernet. After a bit of research and trial and error I was able to build a Linux with Ethernet for this board. What I learnt was mostly about configuring the device tree to enable a specific peripheral (in this case the Ethernet Phy)

Hands on!

While the Vivado tools work perfectly on Windows, whenever Linux development is required, a Linux host machine is required at least for the Petalinux operations. most people would use a Virtual Machine (VM) that is perfectly fine except for the little handicap of not using the full power of the host machine, but there are advantages as well.

I prefer having all Vivado tools installed in an Ubuntu VM so I don't have to transfer files between machines. So in this article I use Vivado on Linux, but it could equally be on Windows. The GUI is very similar, if not the same.

A note on tool versions

I don't necessarily use "the latest" but what it works. In this case I'm using Vivado tools 2020.2 on Ubuntu 18.04.06. I do so because I also develop with Pynq that requires that release and the choice of Ubuntu is because it is supported. If you don't have that restriction, you can probably use another Vivado/ ubuntu release pair to recreate this project.

Create the vivado hardware

Even if we are developing software, a Vivado hardware project is needed. In this case a minimalistic one with just a block diagram and just the Zynq Ultrascale+ MPSoC IP on it.

The processor has to be configured to match the board. Instead of doing that manually because of the many parameters, configuration scripts are available and can be loaded at once. That saves lots of time and potential errors! For this board, the configuration file is available on my github. Just drop the PS on the block diagram, double click on it, click on Presets, then Apply configuration and browse for the configuration file.

Then manually connect the clock to the AXI clock inputs to make it look like above. Validate it for errors and generate a top HDL wrapper. Then generate the bitstream. It will take a few minutes. Then export the hardware (xsa file). I chose the name myir_hw for it. This file will be used later on with Petalinux.

Start with Petalinux

Creating a Linux with Petalinux is simple but depending on the tweaks needed it can become a bit more elaborated. In this case it is quite straightforward. The hardware description file created with Vivado is copied to the Ubuntu home folder. A petalinux project is created with this terminal command:

Then cd to the created folder and use petalinux-configure to fetch the xsa file. Note that 1, it points to the folder where the xsa is, not the file, and 2, that there must be only one xsa file in that folder.

There is just one thing to change in the main configuration GUI. In Subsystem AUTO Hardware Settings > SD/SDIO Settings, change the Primary SD/SDIO to psu_sd_1 and exit saving the changes.

Customize the device tree for Ethernet

The Petalinux project could be built straight away and it would work but wouldn't have Ethernet. The reason is it uses an external Ethernet PHY IC that needs to be specified in the device tree.

The Xilinx PS has four GEM (Gigabit Ethernet MAC) with an RGMII (Reduced Gigabit Media Independent Interface). The external PHY is a Texas Instruments DP83867 and it is hardwired to an MDIO address of 5 (this is important). For the curious, below is the PS configuration showing the GEM3 enabled and the RGMII pins assigned. That configuration is the standard, so they made the board based on that. It could happen that someone makes a board with a different hook up, in that case pins have to be assigned accordingly.

To customize the device tree, Petalinux offers the system-user.dtsi file in <petalinux-project-folder>/project-spec/meta-user/recipes-bsp/device-tree/files/

Open it with a text editor and add the lines below the comment line (blue).

The most important here is the MDIO address (5) in ethernet-phy@5 and in reg = <5>. This address depends on pull resistors in the board and is not even the same for the same Phy. Also, there are many Phy ICs, so this is only valid for the TI DP83867. Instead of copying it, you can get the whole file from my github.

Once this is done, petalinux-build can be kicked off

That will create a number of things in the images/linux folder. Only three files (boot.scr, BOOT.bin and image.ub) are to be copied to a FAT formatted micro SD card.

Then as usual, insert the card onto the board, set the boot mode to boot from it, connect a terminal with USB, set the port and baud rate and turn the board on.

At the end of the boot log it should show the Ethernet being up and running (with an ethernet cable connected to a router).

After the boot ends, log in (name and password: root) and do, for example a wget of any web page. I don't always speak French but when I do I say voilà: