Where is MAC address determined?

[matsbror]

Is the MAC address of the Ethernet interface determined when the FPGA bitstream is generated or is it determined in code? I have built two different versions with different MAC-addresses but I need the MAC address to be fixed because of university network rules.

[jeremy-heath]

Add MAC address to the ethernet portion of the dts file then recompile.
"local-mac-address = [00 0a 35 00 00 01];"

[matsbror]

Thanks but I think I still need more info on this. As far as I know, the dts file is generated by vivado. I am using make.py as the only step to compile, but that would overwrite the dts file.

Then, I am still wondering what determines the mac-address as it is? Is it random?

[jeremy-heath]

linux-on-litex-vexriscv generates the dts automatically and places it itn the ./build//.dts
There will be an ethernet section for each ethernet component; place "local-mac-address = [00 0a 35 00 00 01];" there.

There are "locally administered mac addresses" and manufacturer administered mac addresses. You need to pick based on your application.

[matsbror]

I'm guessing this is the Ethernet section:

            mac0: mac@f0002000 {
                compatible = "litex,liteeth";
                reg = <0xf0002000 0x7c>,
                      <0xf0002800 0x0a>,
                      <0x80000000 0x2000>;
                reg-names = "mac", "mdio", "buffer";
                litex,rx-slots = <2>;
                litex,tx-slots = <2>;
                litex,slot-size = <2048>;
                interrupts = <2>;
                status = "okay";
            };

There's nothing else that it could be (I have attached the full dts here).

However, if I add a mac-address to this section, how do I then recompile to use it as I only know how to run the make.py command which will overwrite this file with a new .dts-file.

[enjoy-digital]

@matsbror: In you case, you are using the LiteEth MAC attached to the CPU, that lets the CPU handle the MAC address by software.
I haven't tried myself @jeremy-heath's change, but to add this, you can either:

• Add it manually to the generated .dts and compile the .dts manually.
• Modify litex_json2dts_linux.py tool to integrate the changes. Since make.py is calling this tool, this would avoid any other manual overwrite.