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154 lines
3.5 KiB
Groff
154 lines
3.5 KiB
Groff
.\" $Id: vkbd.4,v 1.4 2004/11/16 16:49:39 max Exp $
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.\" $FreeBSD$
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.\"
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.Dd August 12, 2004
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.Os
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.Dt VKBD 4
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.Sh NAME
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.Nm vkbd
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.Nd the virtual AT keyboard interface
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.Sh SYNOPSIS
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.Cd "device vkbd"
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.Sh DESCRIPTION
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The
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.Nm
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interface is a software loopback mechanism that can be loosely
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described as the virtual AT keyboard analog of the
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.Xr pty 4 ,
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that is,
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.Nm
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does for virtual AT keyboards what the
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.Xr pty 4
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driver does for terminals.
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.Pp
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The
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.Nm
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driver, like the
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.Xr pty 4
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driver, provides two interfaces: a keyboard interface like the usual
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facility it is simulating (a virtual AT keyboard in the case of
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.Nm ,
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or a terminal for
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.Xr pty 4 ) ,
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and a character-special device
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.Dq control
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interface.
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.Pp
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The virtual AT keyboards are named
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.Pa vkbd0 , vkbd1 ,
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etc., one for each control device that has been opened.
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.Pp
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The
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.Nm
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interface permits opens on the special control device
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.Pa /dev/vkbdctl .
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When this device is opened,
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.Nm
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will return a handle for the lowest unused
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.Pa vkbdctl
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device (use
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.Xr devname 3
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to determine which).
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.Pp
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Each virtual AT keyboard supports the usual keyboard interface
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.Xr ioctl 2 Ns s ,
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and thus can be used with
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.Xr kbdcontrol 1
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like any other keyboard.
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The control device supports exactly the same
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.Xr ioctl 2 Ns s
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as the virtual AT keyboard device.
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Writing AT scan codes to the control device generates an input on
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the virtual AT keyboard, as if the
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(non-existent)
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hardware had just received it.
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.Pp
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The virtual AT keyboard control device, normally
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.Pa /dev/vkbdctl Ns Aq Ar N ,
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is exclusive-open
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(it cannot be opened if it is already open)
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and is restricted to the super-user.
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A
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.Xr read 2
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call will return the virtual AT keyboard status structure
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(defined in
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.In dev/vkbd/vkbd_var.h )
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if one is available;
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if not, it will either block until one is or return
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.Er EWOULDBLOCK ,
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depending on whether non-blocking I/O has been enabled.
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.Pp
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A
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.Xr write 2
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call passes AT scan codes to be
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.Dq received
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from the virtual AT keyboard.
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Each AT scan code must be passed as
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.Vt "unsigned int" .
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Although AT scan codes must be passes as
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.Vt "unsigned int" Ns s ,
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the size of the buffer passed to
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.Xr write 2
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still should be in bytes, i.e.,
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.Bd -literal -offset indent
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static unsigned int codes[] =
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{
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/* Make Break */
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0x1e, 0x9e
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};
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int
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main(void)
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{
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int fd, len;
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fd = open("/dev/vkbdctl0", O_RDWR);
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if (fd < 0)
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err(1, "open");
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/* Note sizeof(codes) - not 2! */
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len = write(fd, codes, sizeof(codes));
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if (len < 0)
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err(1, "write");
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close(fd);
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return (0);
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}
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.Ed
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.Pp
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Write will block if there is not enough space in the input queue.
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.Pp
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The control device also supports
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.Xr select 2
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for read and write.
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.Pp
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On the last close of the control device, the virtual AT keyboard is removed.
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All queued scan codes are thrown away.
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.Sh SEE ALSO
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.Xr kbdcontrol 1 ,
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.Xr atkbdc 4 ,
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.Xr psm 4 ,
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.Xr syscons 4
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.Sh CAVEATS
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The
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.Nm
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interface is a software loopback mechanism, and, thus
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.Xr ddb 4
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will not work with it.
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Current implementation of the
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.Xr syscons 4
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driver can accept input from only one keyboard, even if it is virtual.
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Thus it is not possible to have both wired and virtual keyboard to be active
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at the same time.
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It is, however, in principal possible to obtain AT scan
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codes from the different sources and write them into the same virtual keyboard.
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The virtual keyboard state synchronization is the user's responsibility.
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.Sh HISTORY
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The
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.Nm
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module was implemented in
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.Fx 6.0 .
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.Sh AUTHORS
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.An Maksim Yevmenkin Aq m_evmenkin@yahoo.com
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