CONSOLE(4)						     Kernel Interfaces Manual							CONSOLE(4)

NAME

       console, keyboard, log - system console

DESCRIPTION

       The  TTY  device driver manages two devices related to the main user interface, the system screen and the keyboard.  These two together are
       named "the Console".

   The Screen
       The screen of a PC can be managed by a Monochrome Display Adapter, a Hercules card, a Color Graphics Adapter, an Enhanced Graphics Adapter,
       or a Video Graphics Array.  To the console driver these devices are seen as a block of video memory into which characters can be written to
       be displayed, an I/O register that sets the video memory origin to the character that is to be displayed on the top-left  position  of  the
       screen, and an I/O register that sets the position of the hardware cursor.  Each character within video memory is a two-byte word.  The low
       byte is the character code, and the high byte is the "attribute byte", a set of bits that controls the  way  the  character  is	displayed,
       character and background colours for a colour card, or intensity/underline/reverse video for monochrome.

       These are the characteristics of the adapters in text mode:

	      Adapter	     Usable memory  Mono/Colour
	       MDA	      4K	     M
	       Hercules       4K	     M
	       CGA	      16K	     C
	       EGA	      32K	     M or C
	       VGA	      32K	     M or C

       MDA and Hercules are the same to the console driver, because the graphics mode of the Hercules is of no use to Minix.  EGA and VGA are also
       mostly seen as the same in text mode.  An EGA adapter is either a monochrome or a colour device depending on the screen attached to it.	 A
       VGA adapter can run in either monochrome or colour (grayscale) mode depending on how the Boot Monitor has initialized it.

       The  driver  uses the video origin to avoid copying the screen contents when scrolling up or down.  Instead, the origin is simply moved one
       line.  This is named "hardware scrolling", as opposed to copying memory: "software scrolling".

       The video origin is also used to implement several virtual consoles inside the video memory of the adapter.  Each virtual  console  gets  a
       segment of video memory.  The driver chooses which console to display by moving the video origin.  Note that an MDA or Hercules adapter can
       only support one console.  CGA can support up to four 80x25 consoles, and EGA and VGA can have eight.  It is best  to  configure  one  less
       console to leave some video memory free so that hardware scrolling has some space to work in.

       Character codes are used as indices into a display font that is stored in the adapter.  The default font is the IBM character set, which is
       an ASCII character set in the low 128 codes, and a number of mathematical, greek, silly graphics, and accented characters in the upper  128
       codes.  This font is fixed in the MDA, Hercules and CGA adapters, but can be replaced by a user selected font for the EGA and VGA adapters.

       A  number of control characters and escape sequences are implemented by the driver.  The result is upward compatible with the ANSI standard
       terminal.  The termcap(5) type is minix.  Normal characters written to the console are displayed at the cursor position and the	cursor	is
       advanced  one  column  to  the right.  If an entire line is filled then the cursor wraps to the first column of the next line when the next
       character must be displayed.  The screen is scrolled up if needed to start a new line.  Some characters have special effects when  sent	to
       the  console.  Some even have arguments in the form of comma separated decimal numbers.	These numbers default to the lowest possible value
       when omitted.  The top-left character is at position (1, 1).  The following control characters and escape sequences are implemented by  the
       console:

       Sequence  Name		     Function
	^@	  Null		      Ignored (padding character)
	^G	  Bell		      Produce a short tone from the speaker
	^H	  Backspace	      Move the cursor back one column, wrapping from the left edge up one line to the right edge
	^I	  Horizontal Tab      Move to the next tab stop, with each tab stop at columns 1, 9, 25, etc.  Wrap to the next line if necessary.
	^J	  Line Feed	      Move one line down, scrolling the screen up if necessary
	^K	  Vertical Tab	      Same as LF
	^L	  Form Feed	      Same as LF
	^M	  Carriage Return     Move to column 1
	^[	  Escape	      Start of an escape sequence
	^[M	  Reverse Index       Move one line up, scrolling the screen down if necessary
	^[[nA	  Cursor Up	      Move the cursor up n lines
	^[[nB	  Cursor Down	      Move the cursor down n lines
	^[[nC	  Cursor Forward      Move the cursor right n columns
	^[[nD	  Cursor Backward     Move the cursor left n columns
	^[[m;nH   Cursor Position     Move the cursor to line m, column n
	^[[sJ	  Erase in Display    Clear characters as follows:
				      s = 0: From cursor to end of screen
				      s = 1: From start of screen to cursor
				      s = 2: Entire screen
	^[[sK	  Erase in Line       Clear characters as follows:
				      s = 0: From cursor to end of line
				      s = 1: From start of line to cursor
				      s = 2: Entire line
	^[[nL	  Insert Lines	      Insert n blank lines
	^[[nM	  Delete Lines	      Delete n lines
	^[[n@	  Insert Characters   Insert n blank characters
	^[[nP	  Delete Characters   Delete n characters
	^[[nm	  Character Attribute Set character attribute as follows:
				      n = 0: Normal (default) attribute
				      n = 1: Bold (mono) / Yellow (colour)
				      n = 4: Underline (M) / Light green (C)
				      n = 5: Blinking (M) / Magenta (C)
				      n = 7: Reverse Video
				      n = 30: Black foreground colour
				      n = 31: Red
				      n = 32: Green
				      n = 33: Orange
				      n = 34: Blue
				      n = 35: Magenta
				      n = 36: Light blue
				      n = 37: White
				      n = 40 - 47: Same for background colour

       The console device implements the following ioctl to copy a font into font memory on EGA and VGA adapters:

	      ioctl(fd, TIOCSFON, u8_t font[256][32]);

       Font  memory  consists of 256 character definitions of 32 lines per character and 8 pixels per line.  The first line is the topmost line of
       the character.  The leftmost pixel is lit if the most significant bit of a line is set, etc.  The 80x25 video mode used	by  Minix  has	an
       8x16 character cell, which means that only the first 16 lines of a character are displayed.

   The Keyboard
       The  keyboard  produces	key codes for each key that is pressed.  These keys are transformed into character codes or sequences according to
       the current keyboard translation table.	The format of this table is described in keymap(5).  The character codes can be read from the con-
       sole device unless they map to special hotkeys.	The hotkeys are as follows:

       Name		KeyFunction
	CTRL-ALT-DEL	 Send an abort signal to process 1 (init).  Init then halts the system
	CTRL-ALT-KP-.	 Likewise for keypad period
	F1		 Process table dump
	F2		 Show memory map
	F3		 Toggle software/hardware scrolling
	F5		 Show network statistics
	CTRL-F7 	 Send a quit signal to all processes connected to the console
	CTRL-F8 	 Send an interrupt signal
	CTRL-F9 	 Send  a  kill signal.	If CTRL-F8 or CTRL-F7 don't get 'em, then this surely will.  These keys are for disaster recovery.
			 You would normally use DEL and CTRL- to send interrupt and quit signals.
	ALT-F1		 Select virtual console 0 (/dev/console)
	ALT-F2		 Select virtual console 1 (/dev/ttyc1)
	ALT-F(n+1)	 Select virtual console n (/dev/ttycn)
	ALT-Left	 Select previous virtual console
	ALT-Right	 Select next virtual console

       The keyboard map is set with the KIOCSMAP ioctl whose precise details are currently hidden in the loadkeys utility.

   Log device
       The log device can be used by processes to print debug messages onto the console.  The console is a terminal type device, so  it  is  taken
       from processes when a session leader exits.  This does not happen with the log device.

SEE ALSO

       tty(4), loadkeys(1), keymap(5), boot(8).

NOTES

       Output processing turns Line Feeds into CR LF sequences.  Don't let this surprise you.  Either turn off output processing or use one of the
       synonyms for LF.

AUTHOR

       Kees J. Bot (kjb@cs.vu.nl)

																	CONSOLE(4)