Anti-brick system

The Spectrum Next and the TBBlue have an anti-brick system that allows to recover the machine in case of an unsuccessful update of the firmware.

This system is actually a core that is initialized when the machine is turned on, testing if the M1 and Drive buttons are pressed. If both buttons are pressed, the anti-brick system loads the updater module from SD card and starts it to allow a new update.

When no buttons are pressed, the anti-brick core sends a command to the FPGA to reload a new core recorded in another address of the flash where the Next/TBBlue core is written, essentially booting the machine normally.