@node _bios_keybrd, bios
@findex _bios_keybrd
@subheading Syntax

@example
#include <bios.h>

unsigned _bios_keybrd(unsigned cmd);
@end example

@subheading Description

The @code{_bios_keybrd} function uses INT 0x16 to access the keyboard
services.  The @var{cmd} argument can be any of the following manifest
constants:

@table @code

@item _KEYBRD_READ
read the next key pressed.

@item _NKEYBRD_READ
read the next extended key pressed.  Unlike @code{_KEYBRD_READ}, this
command knows about keys introduced with the AT-style 101-key keyboards,
such as @key{F11} and @key{F12}, and can distinguish between the editing
keys on the numeric pad and the grey keys of the edit pad.  On the other
hand, some of the extended keys return two-byte sequences which
typically begin with the @code{E0h} (224 decimal) prefix, so code that
uses @code{_NKEYBRD_READ} should deal with this complexity.

@item _KEYBRD_READY
check if a key is waiting in the keyboard buffer.

@item _NKEYBRD_READY
check if an extended key is waiting in the keyboard buffer.  Like
@code{_KEYBRD_READY}, but recognizes extended keys such as @key{F12},
which @code{_KEYBRD_READY} ignores.

@item _KEYBRD_SHIFTSTATUS
read keyboard shift state (the byte at the address @code{40h:17h} in the
BIOS data area):

@example
7654 3210  Meaning
---- ---X  Right SHIFT is pressed
---- --X-  Left SHIFT is pressed
---- -X--  CTRL is pressed
---- X---  ALT is pressed
---X ----  Scroll Lock locked
--X- ----  Num Lock locked
-X-- ----  Caps Lock locked
X--- ----  Insert locked
@end example

@item _NKEYBRD_SHIFTSTATUS
read keyboard shift and extended shift state (the byte at the address
@code{40h:17h} in the BIOS data area combined with the extended shift
flags from the bytes at addresses @code{40h:18h} and @code{40h:96h}):

@example
FEDC BA98  7654 3210  Meaning
---- ----  ---- ---X  Right SHIFT is pressed
---- ----  ---- --X-  Left SHIFT is pressed
---- ----  ---- -X--  CTRL is pressed
---- ----  ---- X---  ALT is pressed
---- ----  ---X ----  Scroll Lock locked
---- ----  --X- ----  Num Lock locked
---- ----  -X-- ----  Caps Lock locked
---- ----  X--- ----  Insert locked

---- ---X  ---- ----  Left CTRL is pressed
---- --X-  ---- ----  Left ALT is pressed
---- -X--  ---- ----  Right CTRL is pressed
---- X---  ---- ----  Right ALT is pressed
---X ----  ---- ----  Scroll Lock is pressed
--X- ----  ---- ----  Num Lock is pressed
-X-- ----  ---- ----  Caps Lock is pressed
X--- ----  ---- ----  SysReq is pressed
@end example

@end table

Return Value

With the @code{*_READ} and @code{*_SHIFTSTATUS} arguments, the
@code{_bios_keybrd} function returns the contents of the @sc{ax}
register after the BIOS call.  For the @code{*_READ} arguments, this is
the combination of scan code and ASCII code for alphanumeric keys, or a
scan code and either zero or the @code{E0h} prefix for special keys.

With the @code{*_READY} arguments, @code{_bios_keybrd} returns 0 if no
key is waiting in the BIOS keyboard buffer.  If there is a key,
@code{_bios_keybrd} returns the key waiting to be read (that is, the
same value as the corresponding @code{*_READ} would return).

With the @code{*_READ} and @code{*_READY} arguments, the
@code{_bios_keybrd} function returns -1 if @kbd{Ctrl+@key{BREAK}} has
been pressed and is the next keystroke to be read.

@subheading Portability

@portability !ansi, !posix

@subheading Example

@example
while( !_bios_keybrd(_KEYBRD_READY) )
  try_to_do_something();
@end example