Defined in rt_sys.h, the
_ttywrch() function writes a character to the console.
The console might have been redirected. You can use this function as a last resort error handling routine.
The default implementation of this function uses semihosting.
You can redefine this function, or
even if there is no other input/output. For example, it might write
an error message to a log kept in nonvolatile memory.