How to keep the same MAC address after consecutive build and flash operations

[gc0rreiab]

I'm developing an OpenThread Sleepy End Device (SED) that periodically sends a payload to a CoAP server, including its own MAC address as one of the values. However, I noticed that the MAC address changes every time I build and flash the firmware. How to keep the MAC address persistent across firmware flashes?

My code for retrieving the MAC address:

void get_my_mac_address(char* buf, size_t buf_size) {
  otInstance* myInstance = openthread_get_default_instance();
  const otExtAddress* ext_addr = otLinkGetExtendedAddress(myInstance);
  snprintf(buf, buf_size, "%02X:%02X:%02X:%02X:%02X:%02X:%02X:%02X", ext_addr->m8[0], ext_addr->m8[1], ext_addr->m8[2], ext_addr->m8[3],
           ext_addr->m8[4], ext_addr->m8[5], ext_addr->m8[6], ext_addr->m8[7]);

  LOG_INF("My MAC: %s. (line %i)\n", buf, __LINE__);
}

[Amanda Hsieh]

Hi, 

Do you mean the IEEE 802.15.4 extended address or the IEEE EUI-64 address? Check this post. 

otLinkGetExtendedAddress() function would gets the IEEE 802.15.4 Extended Address. It could be that you are not setting the extended address persistent, so it is changed upon reset/flash.

Regards,
Amanda H.

[gc0rreiab]

If I understand correctly, the IEEE EUI-64 address is a globally unique identifier assigned by the IEEE Registration Authority and consists of a 24-bit Organizationally Unique Identifier (OUI) and a 40-bit unique extension. Nordic Semiconductor likely purchases a block of these addresses and programs one unique EUI-64 into each nRF54x device during manufacturing.

The IEEE 802.15.4 extended address, on the other hand, is a 64-bit MAC address used in IEEE 802.15.4 networks (such as Thread or Zigbee) and it is typically derived from the EUI-64 either by hardware or during software stack initialization. This means the IEEE 802.15.4 extended address can change between resets or reinitializations unless it is explicitly stored and made persistent?

[Amanda Hsieh]

That's correct. 

[gc0rreiab]

What is the expected behavior if the flash memory is erased in the middle of a flashing operation? For example, what happens when I use the Erase Board function while an nRF54L15 DK is connected to my laptop? Will the persistent IEEE 802.15.4 Extended Address be erased and regenerated?

[Amanda Hsieh]

It will be erased.