Intel Extensible Firmware Interface - Manual (Page 301)

Protocols — Console Support
Version 1.10 12/01/02 10-7
Description
The ReadKeyStroke() function reads the next keystroke from the input device. If there is
no pending keystroke the function returns EFI_NOT_READY . If there is a pending keystroke,
then ScanCode is the EFI scan code defined in Table 10-2. The UnicodeChar is the actual
printable character or is zero if the key does not represent a printable character (control key,
function key, etc.).
Status Codes Returned
EFI_SUCCESS The keystroke information was returned.
EFI_NOT_READY There was no keystroke data available.
EFI_DEVICE_ERROR The keystroke information was not returned due to hardware errors.