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)