Firmware panic

[isaacvr]

Feature description

Add ability to freeze firmware execution

Is your feature request related to a problem? Please describe.
If critical crypto conditions detected then device should be locked to prevent access to coins and preserve funds in wallet.

Describe the solution you'd like
Implement a function that relies on built-in device traps to halt device execution .

Describe alternatives you've considered
Setting a flag in order to exit main loop gracefully , might be hijacked (i.e. flag value reverted after failure detected but prior to loop conditional).

Additional context
Skycoin core panics if some (serious) crypto errors are detected at run time . This is to protect coins . Firmware does not support doing so .

Possible implementation

• Add void panic(char *) in error.h
• Trigger EXTI0 ISR from software so as to abandon stack execution context right away and enter an infinite loop in the end
• Send Failure message with Failure_FirmwarePanic reason
• Replace inline TODO comments related to abort() in skycoin-api with a call to panic()
• Implement firmware panic for emulator by displaying error message and disabling all interaction