How to set a custom MAC address on RP2350 + W5500 (MicroPython / WIZNET5K)

[huababua]

Hi all,

I’m working with an RP2350 board and a W5500 (WIZNET5K driver in MicroPython).
When I bring up the interface, it always appears with a generated MAC address that seems to be derived from the board’s unique ID.

For my project (which may go into production), I need to assign a fixed, custom MAC address — either one I provide at runtime or stored in flash.

So far I’ve tried things like:

`import network, ubinascii

nic = network.WIZNET5K(spi, cs, rst)
nic.config(mac=b'\x02\x12\x34\x56\x78\x9a')
nic.active(True)

print(ubinascii.hexlify(nic.config('mac'), `

But the driver seems to overwrite my value with its own generated MAC during initialization.

Questions:
1. Is there an official / supported way in MicroPython to set a custom MAC on the WIZNET5K interface?
2. If not, what’s the recommended workaround — e.g. setting it after active(True), patching the driver, or some other method?
3. For production: is there a clean way to make the MAC persist (e.g. storing it in flash and applying it on startup)?

Any pointers to code examples or the right place in the MicroPython RP2 port / WIZNET driver to patch would be hugely appreciated.

Thanks in advance!

[MilhouseVH]

Have you tried setting the new MAC after active()? I'm fairly sure this was working previously but haven't tested it in a while...

mac = '00:11:22:33:44:55'

nic = network.WIZNET5K(spi, cs, rst)

nic.active(True)

# Set a custom MAC address. Must be exactly 6 hex pairs. Upper or lower case. Colons optional.
nic.config(mac=bytes.fromhex(mac.replace(':', '')))

new_mac = nic.config('mac').hex(':')

[scruss]

See this: Duplicate MAC addresses on W5500 modules? · micropython · Discussion #18070
Short answer: you can't.

[MilhouseVH]

See this: Duplicate MAC addresses on W5500 modules? · micropython · Discussion #18070 Short answer: you can't.

Maybe check again?

Sep 22 23:45:35 dnsmasq-dhcp[748]: DHCPDISCOVER(eth0) 00:11:22:33:44:55
Sep 22 23:45:35 dnsmasq-dhcp[748]: DHCPOFFER(eth0) 192.168.0.216 00:11:22:33:44:55
Sep 22 23:45:35 dnsmasq-dhcp[748]: DHCPREQUEST(eth0) 192.168.0.216 00:11:22:33:44:55
Sep 22 23:45:35 dnsmasq-dhcp[748]: DHCPACK(eth0) 192.168.0.216 00:11:22:33:44:55

[scruss]

I don't have the hardware: they do. Post your solution there

[MilhouseVH]

I don't have the hardware: they do. Post your solution there

I posted it here. Look above.

[sosi-deadeye]

It seems to work.

It was tested with a ESP32-S3-ETH-8DI-8RO-C from Waveshare. A W5500 is used for Ethernet.

[huababua]

Thank you all!