EUI64 Support

[brushlow18]

I am trying to get an EUI64 value from my ESP32, as I want to use it for a LoRaWAN DevEUI value, but I'm unclear where the last four bytes are coming from? The 48-bit MAC is clearly visible in the eFuse, but I'm not sure where the 0xFC3F comes from that gets amended to the 48-bit MAC when I call esp_efuse_mac_get_default().

I'm really trying to determine:
- Is this a valid EUI64?
- How can I reliably read and/or assemble this EUI64 using the python tools (esptool and espefuse)?

Thanks for your help

[MicroController]

Apparently, an EUI-64 is built from a 48-bit MAC by splitting the MAC into 2x 3 bytes and inserting 0xfffe between the halves.
This also seems to be what the IDF does.