linux-kernel - Re: Keys get stuck

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Message-ID: <20080314193534.GB24646@elf.ucw.cz>
Date:	Fri, 14 Mar 2008 20:35:34 +0100
From:	Pavel Machek <pavel@....cz>
To:	Lennart Sorensen <lsorense@...lub.uwaterloo.ca>
Cc:	David Newall <davidn@...idnewall.com>,
	Jiri Kosina <jkosina@...e.cz>, "Fred ." <eldmannen@...il.com>,
	linux-kernel@...r.kernel.org
Subject: Re: Keys get stuck

On Fri 2008-03-14 09:30:19, Lennart Sorensen wrote:
> On Thu, Mar 13, 2008 at 06:14:26PM +0100, Pavel Machek wrote:
> > hw is proper place to implement autorepeat, and along with some
> > buffering, it has chance to work. Kernel is not real-time, and X are
> > definitely not real-time, while autorepeat is real-time operation.
> > 
> > It actually mostly works in ps/2 case. Buffer in hardware means that
> > pretty big interrupt delays can be tolerated without problems.
> 
> So does the keyboard events generate something like this then:
> 
> KEY_x_DOWN
> KEY_x_REPEAT
> KEY_x_UP

Yes, kernel<->user interface is something like that. Try evtest to see
it.

> If so then X certainly could get all the keyboard information I imagine
> it needs from the kernel, but otherwise I am not sure how it could.
> A
> repeated series of key down events are not enough since some keys you
> don't want repeated you just want to know when the key is held down and
> when it isn't.

PS/2 keyboard sends both ups and downs. "down down down up" means
autorepeat. It is not actually ambiguous.

BTW this is what I use to generate huge latencies and cause X
problems:

void
main(void)
{
        int i;
        iopl(3);
        while (1) {
                asm volatile("cli");
                //              for (i=0; i<20000000; i++)
                for (i=0; i<1000000000; i++)
                        asm volatile("");
                asm volatile("sti");
                sleep(1);
        }
}

...run it once per core.
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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