Lockable Teensy 4.0 for commercial products and secure applications

Lockable Teensy 4.0 for commercial products and secure applications.

Secure mode can only be activated on Lockable Teensy. While Standard and Lockable Teensy are identical hardware, the permanent fuse configuation differs. Standard Teensy does not allow changes to fuses affecting boot or other critical configuration. Standard Teensy is meant to safe from "bricking" by programs which could write to fuse memory, but this safety means secure mode can not be activated. Standard Teensy can have a key written and can run encrypted code, but encryption alone is not fully secure. Only Lockable Teensy provides proper code security, and only when a key is written and secure mode is locked.