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

["Brian J. Johnson" <brian.johnson@hpe.com>]

On 11/08/2017 07:34 AM, Heyi Guo wrote:
> 
> 
> On 11/08/2017 05:07 PM, Gerd Hoffmann wrote:
>> On Wed, Nov 08, 2017 at 04:44:37PM +0800, Heyi Guo wrote:
>>>
>>> 在 11/8/2017 4:34 PM, Ni, Ruiyu 写道:
>>>> No.
>>>> Even a terminal tool can recognize F10, it still needs to translate 
>>>> it into "ESC [ V"
>>>> and send the three bytes to firmware.
>>> Got it. But the 2 seconds timeout is not for this situation, right? If
>>> terminal tool could translate and send the key sequence, I think it can
>>> complete 3 bytes transfer in a very short time, isn't it? E.g. 9600 
>>> baud / 8
>>> = 1200 Bytes/s (ignore control bits).
>>>
>>> So 2 seconds timeout is still for user to enter the sequence "ESC [ V"
>>> manually?
>> No.  Alot of software has this kind of delay because it is recommended
>> in some classic unix documentation to avoid mis-interpreting incomplete
>> terminal control sequences coming from slow terminals.
>>
>> Where a "slow terminal" which actually would need such a long delay is a
>> physical terminal from the 70ies of the last century, or a virtual
>> terminal hooked up over a *really* slow network connection.
>>
>> Reducing the delay from 2 seconds to roughly 0.2 seconds should be
>> pretty safe, things are not that slow any more these days :)
> That will be great if we can make such change :)
> 

You'd be surprised how much delay you can get with a few layers of 
firewalls, VPNs, and cross-country (or intercontinental) WAN links. 
That's the advantage of serial:  you can tunnel it anywhere.

Here's a quick workaround:  if you start typing other text after the 
ESC, the terminal driver will see the new keystrokes and resolve the ESC 
immediately, without the delay.  For instance, at the shell prompt, type 
something, press ESC to clear the line, then just start typing new text 
without waiting for the timeout.  The line will be cleared and the new 
text will appear correctly, without delay.

On setup screens, I usually hit escape to return to the previous screen, 
then hit one of the arrow keys to cause the ESC to be processed without 
the timeout.  That works pretty well in practice.

I'd think a PCD to control this delay would be appropriate, though.
-- 
Brian J. Johnson
Enterprise X86 Lab

Hewlett Packard Enterprise