Anti-brick system
From SpecNext official Wiki
The anti-brick system is used to recover from potential corruption of the firmware or FPGA image.
The anti-brick system is a secondary FPGA core which activates when the machine is turned on and runs the updater module from SD card if the M1 and Drive buttons are both pressed.
If the two buttons are not pressed then the FPGA reloads the core that is stored in the updatable firmware.