Make original Arduino ATMEGA328P-AU

The built-in POR circuit only provides a flag to see if it has occurred and does not have a setting register or fuse, so I think it is always active and cannot be disabled.

https://ww1.microchip.com/downloads/en/DeviceDoc/ATmega48A-PA-88A-PA-168A-PA-328-P-DS-DS40002061A.pdf#page=57