Note 1
Permission of the author has been granted to publish this here.
Note 2
This is based on the 1.2.13 kernel, with an addendum for 1.3.28.
I've now checked back from 2.4.12. None of the information below has been changed. The only added feature is console cut-n-paste.
(I used http://lxr.linux.no/blurb.html to check the changes. How very useful.)

Linux Console Driver

(Everything you ever wanted to know but couldn't be bothered to look in the source for.)


Author: Peter L Jones <thanatos@drealm.org>
Date: Wed Sep 27 19:12:25 BST 1995
Kernel: 1.2.13
Addendum for: 1.3.28

General Processing

I've not documented "hardware scrollback".

I don't use UTF. I've only covered it to the extent I can fathom from the source.

In UTF mode, once a complete character is assembled, it is translated.

Otherwise, the character then has its top bit set, if requested, and is then translated.

A glyph is to be displayed if

  • we've assembled a complete UTF character
  • we translated it okay
  • it's not a control character, or we're displaying control characters

Otherwise, it might be a control character.
Otherwise it's ignored.

Glyphs

These are characters that make a "mark" on the display.

You can never display the glyph for char(27) by transmitting ESC.

You cannot display glyphs for any character in the Control Characters table, unless enabled.

If there is a "pending newline"

a crlf sequence is issued prior to the glyph.

If we're in "insert mode",

the rest of the line is shifted right; the character in the last column is lost.

The glyph is then displayed.

If the cursor is in the last column,

If automatic margins are turned on,
the "pending newline" state is set (see earlier)
otherwise,
the next glyph can overwrite this one.
Otherwise the cursor is advanced.

Control Characters

Control characters can occur during ESCape sequence processing.

^g
bell - make a tone on the console speaker
^h
bs (backspace) - cursor to previous character (will not wrap to previous line)
^i
tab - cursor to next tab position
^j ^k ^l
lf (linefeed) - cursor to next line, scroll if end of scrolling region; if CRLF mode select, cr as well
^m
cr (carriage return) - cursor to start of current line
^n
charset 1 - translate table G1, display control characters as glyphs
^o
charset 0 - translate table G0, don't display control characters as glyphs
Note: "charset n" sets the current translate table; e.g. ^n (sets charset 1, translate table G1, display control characters as glyphs) followed by ^[[10m would leave G1 in effect but disable display of control characters as glyphs and display setting the top bit of glyphs.
^x ^z
cancel any ESCape sequence in progress
^[
begin an ESCape sequence
^?
"delete" - ignored
128+^[
begin a CSI sequence

ESCape Sequences

^[[
begin a CSI sequence
^[%
begin a UTF control sequence
^[(
begin a set G0 sequence
^[)
begin a set G1 sequence
^[#
begin a DEC test sequence
^[E
cr, lf
^[M
ri (reverse index) - cursor up, reverse scroll if top of scrolling region
^[D
lf
^[H
set tab in the current column
^[Z
request for terminal ID (response is ^[[?6c - VT102)
^[7
store cursor position
^[8
restore cursor position
^[c
reset terminal completely
^[>
Keypad is numeric (normal)
^[=
Keypad is application (act as function keys)

CSI sequences

There are two formats:

  • Function keys are indicated by CSI [ and are dealt with later.
  • The general format is CSI (i.e. ^[[), zero to 16 parameters (decimal numbers separated by semicolons) and a character to indicate the function being performed. E.g ^[[1;43;37m.

Missing parameters are defaulted. Screen co-ordinates and movements start at and default to 1 (unless otherwise stated). Parameters are named par1, par2 etc in the following descriptions.

CSI h and CSI l can have an optional ? after the CSI and before any parameters. This indicates "DEC Private" modes.
Note:Other manufacturers use different characters to select their private modes - Linux doesn't support any but DEC.

CSI h
Set Mode sequence
CSI l
Clear Mode sequence
CSI n
Request report:
par1 = 5
Status report: response is ^[[0n (terminal okay)
par1 = 6
Cursor report: response is ^[[y;xR - where y is relative if origin mode is selected
CSI A
Cursor Up by par1 lines
CSI F
Cursor Up by par1 lines, and to start of line
CSI B
CSI e
Cursor Down by par1 lines
CSI E
Cursor Down by par1 lines, and to start of line
CSI C
CSI a
Cursor Right by par1 characters
CSI D
Cursor Left by par1 characters
CSI d
Set cursor vertical position to par1
CSI G
CSI `
Set cursor horizonal position to par1
CSI H
CSI f
Set cursor vertical position to par2 and horizontal position to par1
CSI L
Insert par1 lines
CSI M
Delete par1 lines
CSI @
Insert par1 characters
CSI P
Delete par1 characters
CSI X
Erase par1 characters (wraps around line ends)
CSI J
Screen Erase sequence:
par1 = 0
erase from cursor to end of display
par1 = 1
erase from start of display to cursor
par1 = 2
erase whole display
CSI K
Line Clear sequence:
par1 = 0
erase from cursor to end of line
par1 = 1
erase from start of line to cursor
par1 = 2
erase whole line
CSI c
If par1 = 0 (default), requests terminal ID (response is ^[[?6c - VT102)
CSI g
Clear tabs:
par1 = 0
Clears tab at the current column
par1 = 3
Clears all tabs
CSI q
Set LEDs; par1 indicates which LED to turn on - 0 - none, 1 - , 2 - , 3 - .
CSI r
Set scrolling region
par1
top, default and minimum 1, must be less than par2
par2
bottom, default and maximum end of display
CSI s
Store cursor position
CSI u
Restore cursor position
CSI m
Character Rendition sequence
CSI ]
setterm(1) command sequence

Set and Clear Mode Sequences

CSI h sets modes; CSI l clears modes. There are two sets of modes - ANSI standard and DEC private.

ANSI modes:

3
Monitor (display control characters)
4
Insert
20
CRLF

DEC Private modes:

1
Cursor keys as application keys (send ^[Ox as appl, ^[[x as normal)
3
80 (off) or 132 (on) columns
5
Inverse video
6
Origin mode (and go to origin)
7
Autowrap (right margin)
8
Autorepeat
9
Mouse reports #1
25
Cursor visible
1000
Mouse reports #2

Character Rendition Sequences

Each parameter is actioned in order. You cannot get bright backgrounds (rather, I can't).
Author's comment:On SVR4, attribute code 6 is used for bright background, if I remember correctly.

0
default (intensity normal, underline off, blink off, normal video, default colours (which start as white on black))
1
intensity bold
2
intensity dim
21 22
intensity normal
4
underline on
24
underline off
5
blink on
25
blink off
7
reverse video
27
normal video
10
restore translate table, turn off display of control chars, don't set the "top" bit of glyphs displayed
11
disable the translate table, display control chars as glyphs, don't set the "top" bit of glyphs displayed
12
disable the translate table, display control chars as glyphs, set the "top" bit of glyphs displayed
38
underline on, set foreground colour to default
39
underline off, set foreground colour to default
49
set background colour to default
30-37
set foreground colour (0-black, 1-red, 2-green, 3-brown, 4-blue, 5-magenta, 6-cyan, 7-white)
40-47
set background colour (as foreground)

Setterm Commmand Sequences

The command is in par1, followed by parameters.

par1
Description
1
Set underline colour - par2 is 0 to 15, which is 0 to 7 as in set foreground colour above, plus bold versions
2
Set dim colour - par2 as above
8
Store current attributes as defaults (so that CSI 0 m restores to them)
9
Set blanking interval to par2 minutes (max one hour - i.e. 60)

UTF Control Sequences

^[%@
Turn off UTF
^[%G
^[%8
Turn on UTF (^[%8 is deprecated)

G0/G1 Sequences

There are two character sets, known as G0 and G1. G0 is the default character set. Each can be set to one of four mappings. The mappings, and the sequences to select them, are:

G0 G1
Map Name
^[(B ^[)B 0
Normal Map (default G0 map)
^[(0 ^[)0 1
Graphics Map (default G1 map)
^[(U ^[)U 2
Null Map
^[(K ^[)K 3
User Map

The maps themselves are defined in "consolemap.c". "Normal Map" translates the standard IBM PC ROM character set to standard 8-bit ISO Latin-1. "Graphics Map" translates to the VT100 character set in graphics mode. "Null Map" passed the ROM characters straight through, except BS, CR, LF, LL, SO, SI and ESC. "User Map" is available to be changed in the source or by mapscrn(8).

DEC Test Sequences

Only one test, ^[#8, is defined. This fills the display with the character 'E' (to allow the display to be centred).

Addendum

The console driver changed in 1.3.x. This section documents the changes between 1.2.13 and 1.3.28.

Font support is enhanced.

In addition to ESC, some other control characters cannot have their glyphs displayed - ^@ ^H ^J ^L ^M ^N ^O ^[.

Hardware scrollback has been enhanced.

The "Normal Map" has been renamed "Latin 1 Map" (LAT1_MAP).

UTF support has been enhanced.
Note:UTF mode can be used to display the excluded control characters - display UTF character 0xF0cc, where cc is the hex code of the position in the ROM character set to display.

512 byte font support is added.

Font height support allows the screen to resize to fit the font.

A new set of Nonstandard Sequences is defined, prefixed by ESC ]. (setterm commands are still CSI ].)

Each virtual console gains a colour palette, which defines the actual colours used on the display (so you can get yellow rather than brown, for example).

Nonstandard Sequences

^[]P
Set palette. Seven parameters are collected:
par1
is the palette element to redefine (0-7, as set foreground colour above)
par2, par3
set the red component
par4, par5
set the green component
par6, par7
set the blue component
^[]R
Resets the default palette

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