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

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

On 11/24/2017 01:21 AM, Heyi Guo wrote:
> Hi Brian,
> 
> 
> 在 11/9/2017 12:00 AM, Brian J. Johnson 写道:
>> 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.
> 
> Can we really use a PCD in TerminalDxe? I remember some experts in the 
> community said that TerminalDxe is a pure UEFI driver; it can't use PCD 
> since PCD is not defined in UEFI spec.
> 
> Thanks,
> 
> Gary (Heyi Guo)
> 

Gary,

I'm not sure what the rules are for PCDs.  I'm just saying that if 
there's a good way to make the delay configurable for each platform, I 
wouldn't be against it.  2 seconds is a long time in some contexts.

-- 
Brian J. Johnson
Enterprise X86 Lab
Hewlett Packard Enterprise
brian.johnson@hpe.com