[MdeModulePkg/TerminalDxe] Why do we delay 2s for ESC being pressed?

[Heyi Guo <heyi.guo@linaro.org>]

Hi folks,

We found ESC key responded fairly slow on serial port terminal, and we 
think it might be caused by the code in UnicodeToEfiKey in TerminalConIn.c:

     if (UnicodeChar == ESC) {
       TerminalDevice->InputState = INPUT_STATE_ESC;
     }

     if (UnicodeChar == CSI) {
       TerminalDevice->InputState = INPUT_STATE_CSI;
     }

     if (TerminalDevice->InputState != INPUT_STATE_DEFAULT) {
       Status = gBS->SetTimer(
                       TerminalDevice->TwoSecondTimeOut,
                       TimerRelative,
                       (UINT64)20000000
                       );
       ASSERT_EFI_ERROR (Status);
       continue;
     }

It seems we intentionally add 2 seconds delay for ESC key press. This 
provides not so good user experience when we press ESC to exit or cancel 
some operation.

We tried reducing this timeout value to 1 second, then the experience 
improved much and we didn't find any issue introduced.

What's the reason for this timeout value and is there any improvement?

Thanks and regards,

Heyi