Hello Ruiyu,
currently I am struggling a bit with interpreting the UEFI spec concerning the EFI_SIMPLE_TEXT_INPUT_PROTOCOL.
In UEFI spec 2.7. chapter 12.1.2 ConsoleIn Definition there is this sentence:
"Only the control characters defined in Table 100 have meaning in the Unicode input or output streams."
Table 100:
U+0000 Null character ignored when received. U+0008 Backspace. Moves cursor left one column. U+0009 Tab. U+000A Linefeed. Moves cursor to the next line. U+000D Carriage Return. Moves cursor to left margin of the current line.
Rob interpreted this in a patch for U-Boot such that he simply suppressed all other Unicode characters in the 0x00-01F range except for special treatment of 0x001b as ESC.
When I look at EDK2 function USBKeyboardReadKeyStroke() (MdeModulePkg/Bus/Usb/UsbKbDxe/EfiKey.c:700) it seems that EDK2 would pass CTRL+C as Unicode character U+0003 (cf. your patch 608817ad7114 "Change the SimpleTextInEx implementation to return CTRL+C").
The same seems to be the case in function KeyboardReadKeyStroke() (MdeModulePkg/Bus/Isa/Ps2KeyboardDxe/Ps2KbdTextIn.c:265).
So do I get it right that for CTRL+A to CTRL+Z we should return a value U+0001 - U+001a in Key->UnicodeChar and table 100 is about meaning of control characters only and does *not* prescribe a filter?
But what about CTRL+[ - CTRL+_ ? Why are they suppressed in the EDK2 keyboard drivers? How do we enter U+001c - U+001f?
Best regards
Heinrich