PCVT(4) BSD Kernel Interfaces Manual PCVT(4)


pcvt, vt — VT220 virtual screen system console


device vt0

In /boot/device.hints:"isa"


The pcvt driver provides a virtual screen handling system. Probably most important is an emulation of a wide range of DEC VT-220 functionality. See Features for a detailed description.

The pcvt driver requires the keyboard driver atkbd to be also configured in the kernel.


Almost full DEC VT220 functionality (moving towards VT320)

Completely independent virtual terminals for MDA/HGC/CGA/EGA and VGA

25, 28, 35, 40, 43 or 50x80 screen resolution for each virtual screen

Fully remappable keyboard to support national keyboards

All VT220 character sets plus ISO Latin-1 and DEC technical supported

VT220 downloadable character set supported when run on EGA/VGA

VT220 user defined keys for each virtual terminal

Optional function key label support á la Hewlett-Packard terminals

Display function codes functionality

Support for MDA, CGA, EGA and VGA display adaptors

Support for 132 column operation on some VGA chipsets

X Window Support for XFree86 (requires XSERVER to be defined)

What it cannot:

No double wide/high characters

No softscroll

No inverse background

No VT220 printer output support

No VT52 support at all

No 8-bit controls

Only limited AT-keyboard (84 keys) support

Each virtual pcvt virtual terminal has 8 pages of memory attached which are used as a scrollback buffer. By using SHIFT-PageUp and SHIFT-PageDown it is possible to scroll the screen back and forward.

The pcvt console driver is available for the Intel-based FreeBSD operating system. It has been designed to be highly configurable in order to satisfy everyone’s needs. The preferred configuration method is to provide appropriate option lines within the kernel configuration file, possibly overriding the built-in defaults.

The following list gives a short overview of the available configuration options. Refer to the file i386/isa/pcvt/pcvt_conf.h in the kernel source tree for detailed documentation.

Note: The following conventions apply to all Boolean options. If an option value is given as 0, the option is deactivated. With any other value, or no value, the option is activated. If an option is omitted, a built-in default is assumed.


Defines the number of virtual screens.

Default: 8


If activated, a keyboard layout resembling a DEC VT200 (TM) is generated. If deactivated, a mixture between VT220 and HP is used. See the files Keyboard.VT and Keyboard.HP in the pcvt documentation directory for a full description.

Default: off


Enables the builtin screensaver feature.

Default: on


If enabled, a blinking-star screensaver is used. If disabled, the screen is simply blanked (which might be useful for energy-saving monitors).

Default: on


If enabled, the key combination ⟨ Ctrl⟩ ⟨ Alt⟩ ⟨ Del⟩ invokes a CPU reset.

Default: off


Do NOT override a security lock for the keyboard.

Default: on


If enabled, the 25-line modi (VT emulation with 25 lines, and HP emulation with 28 lines) default to 24 lines only to provide a better compatibility to the original DEV VT220 (TM). Thus it should be possible to use the terminal information for those terminals without further changes. Note that this is a startup option; it is possible to toggle between the 24- and 25-lines’ display by the scon(1) utility.

Default: off


If enabled, a sequence composed of ⟨ esc⟩ , followed by the normal key code is emitted if a key is pressed with the ⟨ Alt⟩ key modifier. If disabled, then normal key code with the value 0x80 added is sent.

Default: off

Note that there are further options available which are mainly used for debugging purposes or as a workaround for hardware problems. They are found in i386/isa/pcvt/pcvt_conf.h along with their documentation.

Internal Functions
The functionality described below may be accessed via ioctl(2) system calls with a file descriptor opened on a device node related to the pcvt driver. To make use of them, a program should contain the following line:

#include <machine/pcvt_ioctl.h>

Any parameter definitions cited below can be found in that file.

Keyboard related functions

Three functions are related to basic keyboard hardware:


reset keyboard, set defaults;


get current typematic value, parameter is a pointer to int where the values is stored to;


set current typematic value, similar to above command.

Symbolic values are available for the appropriate constants. To specify the initial typematic delay time, they are KBD_TPD250 for 250 ms through KBD_TPD1000 for 1000 ms, in steps of 250 ms. The typematic repeat rates are KBD_TPM300, specifying 30.0 characters per second through KBD_TPM20 for 2.0 characters per second. The intermediate values are: 30.0, 26.7, 24.0, 21.8, 20.0, 18.5, 17.1, 16.0, 15.0, 13.3, 12.0, 10.9, 10.0, 9.2, 8.6, 8.0, 7.5, 6.7, 6.0, 5.5, 5.0, 4.6, 4.3, 4.0, 3.7, 3.3, 3.0, 2.7, 2.5, 2.3, 2.1, 2.0 characters per second.


get key repetition switch, and


set key repetition switch

again take a pointer to int as argument. They manipulate the drivers internal keyboard repetition flag, possible values are: KBD_REPEATOFF or KBD_REPEATON.


get LED state, and


set LED state manipulate the keyboard indicators, but do not influence the drivers idea of lock key state.

The int where the argument points to may have the values KBD_SCROLLLOCK, KBD_NUMLOCK, KBD_CAPSLOCK, which may be used in any conjunction.


gets state of SCROLL,NUM,CAPS, and


sets state of SCROLL,NUM,CAPS + LEDs

should be used in a same manner to get/set the drivers internal LED flags.

Keyboard remapping

One important feature of the pcvt driver is its ability to overload the built in key definition.


get current key values,


set new key assignment values, and


get original key assignment values

arrange those functions. The take a pointer to a struct kbd_ovlkey as argument as described below. In addition,


removes a key assignment, taking a pointer to an int as argument which contains the affected key number;


removes all key assignments.

struct kbd_ovlkey /* complete definition of a key */
u_short keynum; /* the key itself */
u_short type; /* type of key, see below */
u_char subu; /* subtype, ignored on write */
char unshift[KBDMAXOVLKEYSIZE+1]; /* emitted string, unshifted */
u_char subs; /* subtype, ignored on write */
char shift[KBDMAXOVLKEYSIZE+1]; /* emitted string, shifted */
u_char subc; /* subtype, ignored on write */
char ctrl[KBDMAXOVLKEYSIZE+1]; /* emitted string, control */
u_char suba; /* subtype, ignored on write */
char altgr[KBDMAXOVLKEYSIZE+1]; /* emitted string, altgr */

The appropriate values for the type field are:


no function, key is disabled,


keyboard shift,


alternate shift, sets bit8 to ASCII code,


numeric shift, keypad numeric / application mode,


control code generation,


caps shift - swaps case of letter,


ASCII code generating key,


stop output,


function key,


keypad keys,




AltGr translation feature,


shift lock,


cursor keys, and


’’Return’’ or ’’Enter’’ keys.

The subtype field contains one of the values


key is bound to a string, or


key is bound to a function.

Downloadable character set interface

EGA and VGA video adaptors provide the capability of downloadable software fonts. Since the ’native character set’ of any IBM-compatible PC video board does not allow the full interpretation of DEC multinational character set or ISO Latin-1 (ISO 8859-1), this might be very useful for a U**X environment.


set font attr, and


get font attr

are used to manipulate the drivers information about a downloaded font. The take a pointer to a struct vgafontattr as argument:

struct vgafontattr {
int character_set; /* VGA character set */
int font_loaded; /* Mark font loaded or unloaded */
int screen_size; /* Character rows per screen */
int character_scanlines; /* Scanlines per character - 1 */
int screen_scanlines; /* Scanlines per screen - 1 byte */

Each character of each font is to be downloaded with


load vga char,

taking a pointer to struct vgaloadchar as its argument:

struct vgaloadchar {
int character_set; /* VGA character set to load into */
int character; /* Character to load */
int character_scanlines; /* Scanlines per character */
u_char char_table[32]; /* VGA character shape table */

The field character_set takes the values CH_SET0, CH_SET1, CH_SET2, CH_SET3 on EGA’s or VGA’s. Since VGA’s might have up to eight simultaneously loaded fonts, they can take CH_SET4, CH_SET5, CH_SET6, or CH_SET7, too.

Note that there is a dependence between the font size and a possible screen height (in character rows), depending on the video adaptor used:

Screen size (rows) on: EGA VGA
Font size

8 x 8 43 50
8 x 10 35 40
8 x 14 25 28
8 x 16 not 25

General screen manipulation commands


sets cursor shape,

taking a pointer to the following structure as argument:

struct cursorshape {
int screen_no; /* screen number for which to set, */
/* or -1 to set on current active screen */
int start; /* top scanline, range 0... Character Height - 1 */
int end; /* end scanline, range 0... Character Height - 1 */


set screen info, and


get screen info,

provide an interface to some general driver internal variables which might modify the behaviour of the screens, or which might simply be used to force the driver to switch to one certain screen. Their argument is a pointer to the structure:

struct screeninfo {
int adaptor_type; /* type of video adaptor installed */
/* read only, ignored on write (yet!) */
int totalfonts; /* no of downloadable fonts */
/* read only, ignored on write */
int totalscreens; /* no of virtual screens */
/* read only, ignored on write */
int screen_no; /* screen number, this was got from */
/* on write, if -1, apply pure_vt_mode */
/* and/or screen_size to current screen*/
/* else to screen_no supplied */
int current_screen; /* screen number, which is displayed. */
/* on write, if -1, make this screen */
/* the current screen, else set current*/
/* displayed screen to parameter */
int pure_vt_mode; /* flag, pure VT mode or HP/VT mode */
/* on write, if -1, no change */
int screen_size; /* screen size */
/* on write, if -1, no change */
int force_24lines; /* force 24 lines if 25 lines VT mode */
/* or 28 lines HP mode to get pure */
/* VT220 screen size */
/* on write, if -1, no change */
int vga_family; /* if adaptor_type = VGA, this reflects*/
/* the chipset family after a read */
/* nothing happens on write ... */
int vga_type; /* if adaptor_type = VGA, this reflects*/
/* the chipset after a read */
/* nothing happens on write ... */
int vga_132; /* set to 1 if driver has support for */
/* 132 column operation for chipset */
/* currently ignored on write */

Its field pure_vt_mode may take the values M_HPVT for a mixed VTxxx and HP Mode, with function key labels and a status line, or M_PUREVT for only VTxxx sequences recognized, with no labels.


sets the number of columns for the current screen,

its parameter is a pointer to an integer containing either a value of 80, or a value of 132. Note that setting the number of columns to 132 is only supported on some VGA adaptors. Any unsupported numbers cause the ioctl to fail with errno (see intro(2)) being set to EINVAL.

VGA color palette interface

Only on VGA adaptors, there is a color palette register at the output. It is responsible for the red, green and blue output voltage provided for each of the 256 internal color codes, each lying in the range of 0 through 63 (with 63 representing the brightest value for a base color). Thus, these adaptors map each color code to a color of a ’’palette’’ out of 262144 colors. The commands


read VGA palette entry, and


write VGA palette entry

establish an interface to these palette registers. Their argument is a pointer to:

struct vgapel {
unsigned idx; /* index into palette, 0 .. 255 valid */
unsigned r, g, b; /* RGB values, masked by VGA_PMASK (63) */

Driver identification


returns information if the current compiled in driver is pcvt and its major and minor revision numbers. the call is taking a pointer to the following structure as argument:

struct pcvtid {


/* driver id - string length */

char name[PCVTIDNAMELN];

/* driver name, == PCVTIDSTR


#define PCVTIDNAME "pcvt"

/* driver id - string */

int rmajor;

/* revision number, major



int rminor;

/* revision number, minor


#define PCVTIDMINOR 00


returns information if the current compiled in driver is pcvt and its compile time options. the call is taking a pointer to the following structure as argument:

struct pcvtinfo {

u_int opsys;

/* PCVT_xxx(x)BSD */



#define CONF_386BSD


/* unsupported !!! */





u_int opsysrel;

/* Release for NetBSD/FreeBSD */

u_int nscreens;


u_int scanset;


u_int updatefast;


u_int updateslow;


u_int sysbeepf;


u_int pcburst;


u_int kbd_fifo_sz;


/* config booleans */

u_long compile_opts;

/* PCVT_xxxxxxxxxxxxxxx */


Screen saver

Depending on the configuration of a pcvt driver, there might be a simple screen saver available. It is controlled by the command


set timeout for screen saver in seconds; 0 turns it off,

taking a pointer to an integer as argument. Despite its command name, this is available on any kind of adaptor if configured in by the config(8) option ’’PCVT_SCREENSAVER’’

Compatibility commands for USL-style VT’s

pcvt supports a subset of the USL-style commands used to control the virtual terminal interface. This feature is mainly intended to allow XFree86 to switch between virtual screens even when running an X server. They are ugly with respect to the implied semantics (i.e., they break Berkeley semantics). See the file i386/include/pcvt_ioctl.h for their documentation.


Definitions for ioctl(2) function calls


Device nodes to access the pcvt driver


(relative to the kernel source tree) Documents the various compile-time options to tailor pcvt.


cursor(1), loadfont(1), scon(1), intro(2), ioctl(2), atkbd(4), keyboard(4), config(8), ispcvt(8)


The pcvt driver has been developed for and contributed to 386BSD 0.1. Since then pcvt has become a standard part of FreeBSD, NetBSD and OpenBSD. Since FreeBSD 5.0, pcvt is FreeBSD specific with support for NetBSD and OpenBSD removed to ease further maintenance.


Written by Hellmuth Michaelis <hm [AT]> with much help from Brian Dunford-Shore <brian [AT]> and Jörg Wunsch <joerg [AT]>.

This driver is based on several people’s previous work, notably the historic pccons(4) implementation by William Jolitz <ljolitz [AT]> and Don Ahn, and the keyboard mapping code from Holger Veit <veit [AT]>.


At least one left.

BSD March 26, 2000 BSD