@c -*-texinfo-*-
@c This is part of the XEmacs Lisp Reference Manual.
@c Copyright (C) 1995, 1996 Ben Wing.
@c See the file lispref.texi for copying conditions.
@setfilename ../../info/consoles-devices.info
@node Consoles and Devices, Positions, Frames, top
@chapter Consoles and Devices
@cindex devices
@cindex consoles

  A @dfn{console} is an object representing a single input connection
to XEmacs, such as an X display or a TTY connection.  It is possible
for XEmacs to have frames on multiple consoles at once (even on
heterogeneous types -- you can simultaneously have a frame on an
X display and a TTY connection).  Normally, there is only one
console in existence.

  A @dfn{device} is an object representing a single output device, such
as a particular screen on an X display. (Usually there is exactly one
device per X console connection, but there may be more than one if you
have a multi-headed X display.  For TTY connections, there is always
exactly one device per console.)

  Each device has one or more @dfn{frames} in which text can be
displayed.  For X displays and the like, a frame corresponds to the
normal window-system concept of a window.  Frames can overlap, be
displayed at various locations within the display, be resized, etc.  For
TTY, only one frame can be displayed at a time, and it occupies the
entire TTY display area.

However, you can still define multiple frames and switch between them.
Their contents are entirely separate from each other.  These sorts of
frames resemble the ``virtual console'' capability provided under Linux
or the multiple screens provided by the multiplexing program
@samp{screen} under Unix.

  When you start up XEmacs, an initial console and device are created to
receive input and display frames on.  This will either be an X display
or a TTY connection, depending on what mode you started XEmacs in (this
is determined by the @samp{DISPLAY} environment variable, the
@samp{-nw}, @samp{-t} and @samp{-display} command-line options, etc.).

  You can connect to other X displays and TTY connections by creating
new console objects, and to other X screens on an existing display by
creating new device objects, as described below.  Many functions (for
example the frame-creation functions) take an optional device argument
specifying which device the function pertains to.  If the argument is
omitted, it defaults to the selected device (see below).

@defun consolep object
This returns non-@code{nil} if @var{object} is a console.
@end defun

@defun devicep object
This returns non-@code{nil} if @var{object} is a device.
@end defun

@menu
* Basic Console Functions::     Functions for working with consoles.
* Basic Device Functions::      Functions for working with devices.
* Console Types and Device Classes::
                                I/O and color characteristics.
* Connecting to a Console or Device::
* The Selected Console and Device::
* Console and Device I/O::      Controlling input and output.
@end menu

@node Basic Console Functions
@section Basic Console Functions

@defun console-list
This function returns a list of all existing consoles.
@end defun

@defun console-device-list &optional console
This function returns a list of all devices on @var{console}.  If
@var{console} is @code{nil}, the selected console will be used.
@end defun

@node Basic Device Functions
@section Basic Device Functions

@defun device-list
This function returns a list of all existing devices.
@end defun

@defun device-or-frame-p object
This function returns non-@code{nil} if @var{object} is a device or
frame.  This function is useful because devices and frames are similar
in many respects and many functions can operate on either one.
@end defun

@defun device-frame-list device
This function returns a list of all frames on @var{device}.
@end defun

@defun frame-device frame
This function returns the device that @var{frame} is on.
@end defun

@node Console Types and Device Classes
@section Console Types and Device Classes

Every device is of a particular @dfn{type}, which describes how the
connection to that device is made and how the device operates, and
a particular @dfn{class}, which describes other characteristics of
the device (currently, the color capabilities of the device).

The currently-defined device types are

@table @code
@item x
A connection to an X display (such as @samp{willow:0}).

@item tty
A connection to a tty (such as @samp{/dev/ttyp3}).

@item stream
A stdio connection.  This describes a device for which input and output
is only possible in a stream-like fashion, such as when XEmacs in running
in batch mode.  The very first device created by XEmacs is a terminal
device and is used to print out messages of various sorts (for example,
the help message when you use the @samp{-help} command-line option).
@end table

The currently-defined device classes are
@table @code
@item color
A color device.

@item grayscale
A grayscale device (a device that can display multiple shades of gray,
but no color).

@item mono
A device that can only display two colors (e.g. black and white).
@end table

@defun device-type device
This function returns the type of @var{device}.  This is a symbol whose
name is one of the device types mentioned above.
@end defun

@defun device-or-frame-type device-or-frame
This function returns the type of @var{device-or-frame}.
@end defun

@defun device-class device
This function returns the class (color behavior) of @var{device}.  This
is a symbol whose name is one of the device classes mentioned above.
@end defun

@defun valid-device-type-p device-type
This function returns whether @var{device-type} (which should be a symbol)
species a valid device type.
@end defun

@defun valid-device-class-p device-class
This function returns whether @var{device-class} (which should be a symbol)
species a valid device class.
@end defun

@defvar terminal-device
This variable holds the initial terminal device object, which
represents XEmacs's stdout.
@end defvar

@node Connecting to a Console or Device
@section Connecting to a Console or Device

@defun make-device &optional type device-data
This function creates a new device.
@end defun

The following two functions create devices of specific types and are
written in terms of @code{make-device}.

@defun make-tty-device &optional tty terminal-type 
This function creates a new tty device on @var{tty}.  This also creates
the tty's first frame.  @var{tty} should be a string giving the name of
a tty device file (e.g. @samp{/dev/ttyp3} under SunOS et al.), as
returned by the @samp{tty} command issued from the Unix shell.  A value
of @code{nil} means use the stdin and stdout as passed to XEmacs from
the shell.  If @var{terminal-type} is non-@code{nil}, it should be a
string specifying the type of the terminal attached to the specified
tty.  If it is @code{nil}, the terminal type will be inferred from the
@samp{TERM} environment variable.
@end defun

@defun make-x-device &optional display argv-list
This function creates a new device connected to @var{display}.  Optional
argument @var{argv-list} is a list of strings describing command line
options.
@end defun

@defun delete-device device
This function deletes @var{device}, permanently eliminating it from use.
This disconnects XEmacs's connection to the device.
@end defun

@defvar create-device-hook
This variable, if non-@code{nil}, should contain a list of functions,
which are called when a device is created.
@end defvar

@defvar delete-device-hook
This variable, if non-@code{nil}, should contain a list of functions,
which are called when a device is deleted.
@end defvar

@defun console-live-p object
This function returns non-@code{nil} if @var{object} is a console that
has not been deleted.
@end defun

@defun device-live-p object
This function returns non-@code{nil} if @var{object} is a device that
has not been deleted.
@end defun

@defun device-x-display device
This function returns the X display which @var{device} is connected to,
if @var{device} is an X device.
@end defun

@node The Selected Console and Device
@section The Selected Console and Device

@defun select-console console
This function selects the console @var{console}.  Subsequent editing
commands apply to its selected device, selected frame, and selected
window.  The selection of @var{console} lasts until the next time the
user does something to select a different console, or until the next
time this function is called.
@end defun

@defun selected-console
This function returns the console which is currently active.
@end defun

@defun select-device device
This function selects the device @var{device}.
@end defun

@defun selected-device &optional console
This function returns the device which is currently active.  If optional
@var{console} is non-@code{nil}, this function returns the device that
would be currently active if @var{console} were the selected console.
@end defun

@node Console and Device I/O
@section Console and Device I/O

@defun console-disable-input console
This function disables input on console @var{console}.
@end defun

@defun console-enable-input console
This function enables input on console @var{console}.
@end defun

Each device has a @dfn{baud rate} value associated with it.
On most systems, changing this value will affect the amount of padding
and other strategic decisions made during redisplay.

@defun device-baud-rate &optional device
This function returns the output baud rate of @var{device}.
@end defun

@defun set-device-baud-rate device rate
This function sets the output baud rate of @var{device} to @var{rate}.
@end defun
