.\" $OpenBSD: wsdisplay.4,v 1.8 2001/12/14 18:00:42 mpech Exp $
.\" $NetBSD: wsdisplay.4,v 1.5 2000/05/13 15:22:19 mycroft Exp $
.\"
.Dd March 20, 1999
.Dt WSDISPLAY 4
.Os
.Sh NAME
.Nm wsdisplay
.Nd generic display device support in wscons
.Sh SYNOPSIS
.Cd wsdisplay* at ega? console ?
(EGA display on ISA)
.Cd wsdisplay* at vga? console ?
(VGA display on ISA or PCI)
.Cd wsdisplay* at pcdisplay? console ?
(generic PC (ISA) display)
.Cd wsdisplay* at tga? console ?
(DEC TGA display, alpha only)
.Cd wsdisplay* at nextdisplay? console ?
(NeXT display)
.Cd wsdisplay* at sti? console ?
(HP CRX and Visualize series framebuffers)
.Cd wsdisplay0 at smg0
(VAXstation small monochrome display)
.Cd options WSDISPLAY_DEFAULTSCREENS=N
.Sh DESCRIPTION
The
.Nm
driver is an abstraction layer for display devices within the
.Xr wscons 4
framework.
It attaches to the hardware specific display device driver and
makes it available as text terminal or graphics interface.
.Pp
A display device can have the ability to display characters on it
(without help of an X server), either directly by hardware or through
software drawing pixel data into the display memory.
Such displays are called
.Dq emulating ,
the
.Nm
driver will connect a terminal emulation module and provide a
tty-like software interface.
In contrary, non-emulating displays can only be used by special programs
like X servers.
.Pp
The
.Em console
locator in the configuration line refers to the device's use as output
part of the operating system console.
A device specification containing a positive value here will only match
if the device is in use as system console.
(The console device selection in early system startup is not influenced.)
This way, the console device can be connected to a known
.Xr wsdisplay 4
device instance.
(Naturally, only
.Dq emulating
display devices are usable as console.)
.Pp
The logical unit of an independent contents displayed on a display
(sometimes referred to as
.Dq virtual terminal
) is called a
.Dq screen
here.
If the underlying device driver supports it, multiple screens can
be used on one display.
(As of this writing, only the
.Xr vga 4
and the
.Tn VAX
.Dq smg
display drivers provide this ability.)
Screens have different minor device numbers and separate tty instances.
One screen possesses the
.Dq focus ,
this means it is displayed on the display and its tty device will get
the keyboard input.
(In some cases, if no screen is set up or if a screen
was just deleted, it is possible that no focus is present at all.)
The focus can be switched by either special keyboard input (typically
CTL-ALT-Fn) or an ioctl command issued by a user program.
Screens are set up or deleted through the
.Pa /dev/ttyCcfg
control device (preferably using the
.Xr wsconscfg 8
utility).
Alternatively, the compile-time option
.Cm WSDISPLAY_DEFAULTSCREENS=N
will set up N screens of the display driver's default type and using
the system's default terminal emulator at autoconfiguration time.
.Pp
In addition and with help from backend drivers the following features
are also provided:
.Bl -bullet
.It
Loading, deleting and listing the loaded fonts.
.It
Browsing backwards in the screen output, the size of the
buffer for saved text is defined by the particular hardware driver.
.It
Blanking the screen by timing out on inactivity in the
screen holding the input focus.
Awakening activities consist of:
.Pp
.Bl -bullet -compact
.It
pressing any keys on the keyboard;
.It
moving or clicking the mouse;
.It
any output to the screen.
.El
.Pp
Blanking the screen is usually done by disabling the horizontal sync
signal on video output, but may also include blanking the vertical
sync in which case most monitors go into power saving mode.
See
.Xr wsconsctl 8
for controlling variables.
.El
.Pp
Consult the back-end drivers' documentation for which features are supported
for each particular hardware type.
.Sh FILES
.Bl -tag -width /usr/include/dev/wscons/wsconsio.h -compact
.It Pa /dev/ttyC*
terminal devices (per screen)
.It Pa /dev/ttyCcfg
control device
.It Pa /usr/include/dev/wscons/wsconsio.h
.El
.Sh SEE ALSO
.Xr ega 4 ,
.Xr pcdisplay 4 ,
.Xr tty 4 ,
.Xr tga 4 ,
.Xr vga 4 ,
.Xr wscons 4 ,
.Xr wsconscfg 8 ,
.Xr wsconsctl 8 ,
.Xr wsfontload 8
.Sh BUGS
The
.Nm
code currently limits the number of screens on one display to 8.
.Pp
The terms
.Dq wscons
and
.Dq wsdisplay
are not cleanly distinguished in the code and in manual pages.
.Pp
.Dq non-emulating
display devices are not tested.