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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.


void _ttywrch(int ch);


The default implementation of this function uses semihosting.

You can redefine this function, or __raise(), even if there is no other input/output. For example, it might write an error message to a log kept in nonvolatile memory.