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Re: questions about keyboard

To: Linux/MIPS Development <linux-mips@linux-mips.org>
Subject: Re: questions about keyboard
From: Jan-Benedict Glaw <jbglaw@lug-owl.de>
Date: Thu, 15 Apr 2004 22:22:18 +0200
In-reply-to: <F71A246055866844B66AFEB10654E7860F1B10@riv-exchb6.echostar.com>
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References: <F71A246055866844B66AFEB10654E7860F1B10@riv-exchb6.echostar.com>
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On Thu, 2004-04-15 14:08:54 -0600, Xu, Jiang <Jiang.Xu@echostar.com>
wrote in message 
<F71A246055866844B66AFEB10654E7860F1B10@riv-exchb6.echostar.com>:
> Thanks for the reply, I did some testing and found some interesting things:
> 
> 1.  Everytime I push the key on the keyboard, I can see something out from
> /dev/input/event0 by "cat /dev/input/event0".
> However, I don't see a directory named "proc/input", did I miss configure
> something in the kernel?

Maybe your kernel isn't configured with CONFIG_PROC_FS=y ?
Maybe it's not mounted?

> 2.  read() does work and is a blocking read.  However, if I use select, then
> it does not work.
> Select() never detects the state change.
> Here is the sample code I am using:
> {
>    int test_fd = -1;

No need to initialize - you're assigning a value before accessing it.

>    fd_set rfds;
>    struct timeval tv;
>   
>    tv.tv_sec = 1;
>    tv.tv_usec = 0;

tv_* need to be set before *every* select () invocation, not only once.

>    test_fd = open("/dev/input/event0", O_RDONLY); 
>    if( test_fd < 0 )
>      exit(0);
>    
>    while( 1 )
>    {  
>       FD_ZERO(&rfds);
>       FD_SET(test_fd, &rfds);
>       retval = select( 1, &rfds, NULL, NULL, &tv );

That's wrong. The "1" should be "fd + 1".

>       if( retval )
>          printf("\nDetects something....");

A negative retval would also be != 0 ...

>    }
> }
> 
> What could be wrong?

Most probably it's the hardcoded "1" with the select. That is, select
only looks at all fd's which are smaller than one, so only fd=0 would be
testes, but this one isn't in the set, so...

MfG, JBG

-- 
   Jan-Benedict Glaw       jbglaw@lug-owl.de    . +49-172-7608481
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