VKBD(4) 						   BSD Kernel Interfaces Manual 						   VKBD(4)

NAME

     vkbd -- the virtual AT keyboard interface

SYNOPSIS

     device vkbd

DESCRIPTION

     The vkbd interface is a software loopback mechanism that can be loosely described as the virtual AT keyboard analog of the pty(4), that is,
     vkbd does for virtual AT keyboards what the pty(4) driver does for terminals.

     The vkbd driver, like the pty(4) driver, provides two interfaces: a keyboard interface like the usual facility it is simulating (a virtual AT
     keyboard in the case of vkbd, or a terminal for pty(4)), and a character-special device ``control'' interface.

     The virtual AT keyboards are named vkbd0, vkbd1, etc., one for each control device that has been opened.

     The vkbd interface permits opens on the special control device /dev/vkbdctl.  When this device is opened, vkbd will return a handle for the
     lowest unused vkbdctl device (use devname(3) to determine which).

     Each virtual AT keyboard supports the usual keyboard interface ioctl(2)s, and thus can be used with kbdcontrol(1) like any other keyboard.
     The control device supports exactly the same ioctl(2)s as the virtual AT keyboard device.	Writing AT scan codes to the control device gener-
     ates an input on the virtual AT keyboard, as if the (non-existent) hardware had just received it.

     The virtual AT keyboard control device, normally /dev/vkbdctl<N>, is exclusive-open (it cannot be opened if it is already open) and is
     restricted to the super-user.  A read(2) call will return the virtual AT keyboard status structure (defined in <dev/vkbd/vkbd_var.h>) if one
     is available; if not, it will either block until one is or return EWOULDBLOCK, depending on whether non-blocking I/O has been enabled.

     A write(2) call passes AT scan codes to be ``received'' from the virtual AT keyboard.  Each AT scan code must be passed as unsigned int.
     Although AT scan codes must be passes as unsigned ints, the size of the buffer passed to write(2) still should be in bytes, i.e.,

	   static unsigned int	   codes[] =
	   {
	   /*	   Make    Break */
		   0x1e,   0x9e
	   };

	   int
	   main(void)
	   {
		   int	   fd, len;

		   fd = open("/dev/vkbdctl0", O_RDWR);
		   if (fd < 0)
			   err(1, "open");

		   /* Note sizeof(codes) - not 2! */
		   len = write(fd, codes, sizeof(codes));
		   if (len < 0)
			   err(1, "write");

		   close(fd);

		   return (0);
	   }

     Write will block if there is not enough space in the input queue.

     The control device also supports select(2) for read and write.

     On the last close of the control device, the virtual AT keyboard is removed.  All queued scan codes are thrown away.

SEE ALSO

     kbdcontrol(1), atkbdc(4), psm(4), syscons(4)

CAVEATS

     The vkbd interface is a software loopback mechanism, and, thus ddb(4) will not work with it.  Current implementation of the syscons(4) driver
     can accept input from only one keyboard, even if it is virtual.  Thus it is not possible to have both wired and virtual keyboard to be active
     at the same time.	It is, however, in principal possible to obtain AT scan codes from the different sources and write them into the same vir-
     tual keyboard.  The virtual keyboard state synchronization is the user's responsibility.

HISTORY

     The vkbd module was implemented in FreeBSD 6.0.

AUTHORS

     Maksim Yevmenkin <m_evmenkin@yahoo.com>

BSD
								  August 12, 2004							       BSD