Re: [Discuss] What is causing C2? / USB autosuspension?

Re: [Discuss] What is causing C2? / USB autosuspension?

[Oliver Neukum]

Am Mittwoch 07 Mai 2008 00:24:58 schrieb Alan Jenkins:
> I think I've worked out how to avoid the lost key-presses.  Sometimes
> they get lost; sometimes they don't.  The difference seems to how long I
> wait after the keyboard suspends.  If I wait a few seconds after it's
> suspended (as shown by the LEDs), then it resumes flawlessly.  It should
> be possible to reduce the impact of the hardware misfeature by
> increasing the timeout.  The longer the keyboard has been idle already,
> the lower the probability it'll be used in the next few seconds. 

This suggests a possible work around. Keyboards known to be buggy in this
way could be reawoken periodically before the critical amount of time is over.
How long is that time? What percentage of time does a keyboard need to be
suspended for a positive energy balance?

	Regards
		Oliver
--
To unsubscribe from this list: send the line "unsubscribe linux-input" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html

Re: What is causing C2? / USB autosuspension?

[Alan Jenkins]

Oliver Neukum wrote:
> Am Mittwoch 07 Mai 2008 00:24:58 schrieb Alan Jenkins:
>   
>> I think I've worked out how to avoid the lost key-presses.  Sometimes
>> they get lost; sometimes they don't.  The difference seems to how long I
>> wait after the keyboard suspends.  If I wait a few seconds after it's
>> suspended (as shown by the LEDs), then it resumes flawlessly.  It should
>> be possible to reduce the impact of the hardware misfeature by
>> increasing the timeout.  The longer the keyboard has been idle already,
>> the lower the probability it'll be used in the next few seconds. 
>>     
>
> This suggests a possible work around. Keyboards known to be buggy in this
> way could be reawoken periodically before the critical amount of time is over.
> How long is that time? What percentage of time does a keyboard need to be
> suspended for a positive energy balance?
>   
Sorry, I didn't explain that very clearly.

The problem happens if the keyboard resumes _immediately after_ it's 
autosuspended.  If I start typing as soon as the LED goes off, it loses 
some of the keypresses.  If I instead wait a few seconds before typing, 
it works flawlessly.  Since it's the keyboard that's resuming itself I 
don't think you could fix this.  Unless it's your code that's buggy and 
not the keyboard :-).

What I was trying to say was that I can mitigate this problem by 
increasing the autosuspend timeout from the default of 2 seconds.  I 
will quite often pause for periods of about 2 seconds while typing.  But 
if the keyboard is only suspended after 60 seconds of inactivity or 
longer, then it's far less likely that I will start typing immediately 
afterwards.

Alan

Re: [Discuss] What is causing C2? / USB autosuspension?

[Oliver Neukum]

Am Mittwoch 07 Mai 2008 15:17:27 schrieb Alan Jenkins:
> The problem happens if the keyboard resumes _immediately after_ it's 
> autosuspended.  If I start typing as soon as the LED goes off, it loses

OK, I misunderstood you. Yes, there's nothing I can do. Your hardware
is broken.

	Regards
		Oliver

--
To unsubscribe from this list: send the line "unsubscribe linux-input" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html