With semihosting the target can do keyboard input, screen output, and file I/O on the host.

Standard ARMv6-M/ARMv7-M semihosting is supported, i.e. you can build your application in a special way to have calls to certain functions (open(), close(), read(), write(), lseek(), rename(), unlink(), stat(), isatty(), system()) executed on the debugging host itself. To make use of these facilities, add --specs=rdimon.specs and -lrdimon to the linker flags for your firmware.

If you’re going to use stdin, stdout or stderr (e.g. via printf()/scanf()) and you’re not using newlib’s C runtime (by specifying -nostartfiles), you need to add this to your initialisation:

void initialise_monitor_handles(void);

Arm Arduino users can use the semihosting library from the Library Manager.

These documents from ARM describes the low level interface the target must implement: