SVGATextMode - Textmode manipulation/enhancement tool

SVGATextMode [ -ndhrfcvsam ] [ -t ConfigFile ] [ TextmodeLabel ]

SVGATextMode provides a means to seriously enhance the looks of your Linux text consoles, by re-programming the (S)VGA hardware. It uses a configuration file similar to the one the XFree86 X-windows server uses (Xconfig or XF86Config) to set up better looking textmodes. (=higher resolution, larger font size, higher display refresh...).

It works independently of what text modes are allowed from the BIOS. In theory, any text mode size is possible, as long as your VGA card is up to the job. Whether it is or not, depends greatly on the chipset.

SVGATextMode can resize the console screen on the fly, without rebooting, to any other size. The configuration file holds all the parameters needed for the new mode.

It needs kernel version 1.1.54 or newer if screen resizing is to be possible.

Supported chipsets

Example output:

OPTIONS

Example

In order to be able to do anything, SVGATextMode must be run by the superuser, or it must be setuid root.

Having SVGATextMode installed with the SETUID bits ON makes it run as root, even when a non-root user runs it. This is a potential security problem, since SVGATextMode can be made to execute external programs (font loader and ResetProg).

The default distribution will NOT renounce superuser rights EVER, so it'll run any external program as root also (if the setuid bits on SVGATextMode are on, of course). If you are administering a critical system, don't set the SETUID bits on SVGATextMode (which will have the side effect that non-root users cannot use SVGATextMode), or if you do, make sure that all externally called programs are secure.

If you want to have the SUID bits on, but don't trust the external program's security, then recompiling SVGATextMode with the compile-time option "RUN_SECURE" enabled will make SVGATextMode renounce superuser rights immediately after requesting rights to write to the VGA registers. Any program run thereafter will be run with the user ID of the one executing SVGATextMode.

If the programs called by SVGATextMode are not setuid root, they might fail, because they want to change things only root is allowed to tamper with.

There is a DOS version of all SVGATextMode tools (including SVGATextMode itself) included in the distribution.

The stm.exe program will do the same, and require the same as SVGATextMode under Linux, with the following exceptions:

*

The TextConfig file is in \etc\textconf. Note the lack of a drive letter. You have to execute stm.exe from the same drive the textconf file is on. Otherwise, use the -t option to specify a full textconf file path.

*

No font loading (yet?). Do not enable the "loadfont" option in the textconf file. It will not work: there is no DOS font loader included in the SVGATextMode distribution. This basically means you are limited to modes that still work with the same font you started with. There are no doubt numerous font loaders available for DOS that could solve this problem.

*

Stm.exe is really of limited use. DOS was not designed to have flexible screen sizes (DOS was not designed - period. DOS was patched). DOS programs follow the same route. Some DOS programs assume a certain screen size (like 80x25). Many assume at least a constant screen width (80 chars). Only a few support all screen sizes without trouble. You can expect DOS versions of UNIX tools to be of the last kind (like the editor joe.exe).

*

Running stm.exe in a Windows DOS box IS possible, although you must remain 80 chars wide, or Windows will report that "due to the way this program uses the VGA, it must be run full-screen". If you run stm.exe to change from a 80x25 screen to a 80x50 screen, the DOS box will auto-resize to the new height.

Probaby zillions of them. And for a program that must be run as root, and that changes hardware registers, this is not a good thing.

mode switching

SVGATextMode's purpose is to change the previous text mode into the new one. It only changes those VGA registers that determine the text mode size. Any other register is left untouched. This has the advantage that the special (tricky) registers that were set up by the BIOS when the machine booted remain unchanged, so SVGATextMode doesn't need to have the intelligence built-in to deal with all kinds of special settings.

The downside of this is that it can only go from one text mode to another. In most cases, SVGATextMode cannot switch to text mode from a non-text screen (e.g. from graphics mode, or from a messed-up screen when some graphical application exits ungracefully).

chipset

SVGATextMode does not even try to detect the VGA chipset you are using. This means that if you configure it for an S3 chip, but there's a Cirrus Logic under the bonnet, you'll get a similar effect as when you try to use diesel fuel in a petrol engine...

kernel version

You need at least kernel version 1.1.54 to be able to resize the screen to some other X/Y dimension than is currently being used. The program will refuse to resize the screen when it detects an older kernel version.

out of memory

When the system is under heavy load, screen resizing could bail out with an `out of memory' error. The reason for this is rather obscure, but it boils down to the fact that you need to have at least a certain amount of free, contiguous RAM if you want to avoid this. The amount depends on the requested screen size. On most linux systems (which have a maximum possible amount of 64 virtual consoles), this is:

X * Y * 2 * 64

bytes of memory, where X is the number of characters per line, and Y the number of text lines on the screen.

When the kernel fails to resize the screen because of a lack of the right kind of memory, SVGATextMode tries to free some more by temporarily requesting a large block of memory and freeing it immediately again, forcing some disk buffers to be flushed to disk, and forcing some programs to be swapped out.

If the resizing still fails, it tries to free twice that much memory, and if that fails, three times the amount. If you attempt to resize to a really big screen, this is resp. 2, 4 and 6 MB of memory that will be "freed" before trying to resize the screen. If all that fails, then SVGATextMode will finally give up, and announce this in a large, friendly error message.

The -m option is a way around this, but it has its own problems. When it temporarily switches to a 1x1 screen in order to free some more memory, some other process might snatch memory away from under it before SVGATextMode can switch back to the new mode, causing the final resize to the new size to fail. This is very unlikely to happen, but when it does, you are left with a 1x1 screen, which is rather small. When that happens, blindly stopping some jobs, and blindly resizing to a 80x25 mode (either through SVGATextMode or set80) is the only solution.

A much better option to avoid out-of-memory problems is to tell the kernel it needs to keep more memory free, by swapping a little sooner. This can be done only in Linux kernels from somewhere around the 1.3.60's and up, using /prov/sys/vm/freepages. The default contents of this configuration "file" are:

32 48 64

These numbers represent the amount of free pages (one page is 4096 bytes on an Intel platform) below which the kernel will begin to swap pages out or reduce buffer sizes aggressively, moderately and lightly, resp. All this means that in the default case, an unloaded machine will saturate towards 64 free pages (256k) free memory. Changing these settings to higher values, e.g.

cat 128 256 1024 >/proc/sys/vm/freepages

will cause an unloaded machine to have 4M free memory after a while. This will reduce the risk of running out of memory for SVGATextMode resizing significantly.

Slow startup

This is more a feature than a bug, but it could bother you at some time that SVGATextMode starts up extremely slow. This only happens when you are starting SVGATextMode from a non-working text mode (screen blank, monitor doesn't sync,...).

While experimenting with mode timings, at some point you could end up with a mode that the VGA card cannot handle, and it just stops outputting anything at all: no video, no sync, nothing.

SVGATextMode does its work in the vertical blanking interval, waiting for a vertical sync signal before starting to change VGA registers. But when there is no sync, it would wait forever. A timeout of one second prevents that, but shows up as a relatively long delay before the new mode becomes active.

In addition to that, the default TextConfig file has the "SyncDisks" option active, which makes SVGATextMode execute a "sync" instruction to flush all remaining data in the disk cache to disk. Since there is no way to know when that has finished, SVGATextMode just waits a good while (a few seconds), hoping that all data is flushed by the time it starts.

Your worst nightmare: SVGATextMode bails out!

SVGATextMode works its way through the VGA register programming sequentially, working its way through all the registers one at a time. When it encounters some kind of error in the middle, it will most probably bail out with an error message.

But that message will not be of much use, since leaving those VGA registers halfway programmed will most probably result in no video at all. So the message is there, telling you in all detail what went wrong, but you will not be able to see it...

The author has been made aware of this problem on various occasions, and future versions will not be as unforgiving.

In the mean time, make sure nothing will go lost when you first experiment with SVGATextMode and you have to reboot to get back into a visible text mode. Preferably use `savetextmode' from svgalib to enable a future `textmode' restore command when something goes wrong. Also consider redirecting standard error to a file when you expect trouble. You can then inspect the result when (or "if" ;-) you get back your screen.

There are some nasty interactions with other programs that do VGA programming. Amongst them are: the XFree86 XWindows server, svgalib, dosemu and probably others. The most common effect is a distorted screen when such a program switches back to text mode. The real reason for this mostly lies with that program, because it doesn't restore all VGA chip registers as they were before that program started. They were all written a long time before SVGATextMode saw the light of day, so how could they know?

SVGATextMode cannot really solve this problem, since it exits after setting the new mode, and so it doesn't stay active to restore the mode whenever another one screws it up.

For a more in-depth discussion of these kinds of problems, read the doc/FAQ file in the SVGATextMode distribution.

XFree86

Most problems with XFree86 happen when you change the text mode after X has been started. The X-server remembers all VGA chip settings when it first starts up, and never seems to check them again. So when you start X, switch back to text mode while X is still running, then change the text mode to something else, switch back to X, and then back to text mode, you're in trouble.

X has restored the VGA register contents of when it started, which are not the same that you programmed with SVGATextMode. But the kernel still thinks you are in the new mode, since X didn't tell it about the restoration to the old values, and thus the kernel draws its characters in the wrong place in the video memory.

Result: screen completely garbled. Solution: re-running SVGATextMode whenever you switch back from X to text mode, or exit X, and restart it after re-programming the new text mode.

The former case will need the -a option to tell SVGATextMode to force a full resize. When X restores the VGA register contents, it doesn't restore the tty settings, nor the kernel screen size parameters. Thus SVGATextMode is made to believe that the screen is not resized, and thus doesn't do all the resizing code, leaving the kernel parameters and tty settings as they were: wrong.

A general rule of thumb to avoid interaction-problems with the X-server is to specify as much as possible, thus allowing the server as little guesswork as possible. This is recommended by the XFree86 manuals also, even without SVGATextMode. In practice this means you let the server guess for all hardware parameters just once, i.e. when you first install it on a new VGA card, and preferably from a non-tweaked textmode (no SVGATextMode). You then copy as much parameters from the probe to the XF86Config file as possible. The reason for this is that some probing routines in the XFree86 server work well only under a standard text mode (e.g. the S3 IBM RGB RAMDAC RefClk probe).

other X-servers

If you thought XFree86 was evil for doing this, keep in mind that some commercial X-servers (e.g. Accelerated-X from Xinside) for Linux are even worse (don't shoot me guys! They are absolutely MARVELOUS X-servers, but their textmode support is not just bad, it's non-existent).

They _assume_ you start from a 80x25 screen, and will always return to a 80x25 screen when doing a VT-switch or when exiting the server. Since they don't tell the linux kernel what they've just done, the linux kernel, still thinking it's in some weirdo text mode, will draw its characters all over the place, except in the right one... A partial solution is to change the `startx' script to make it re-run SVGATextMode after the server exits. But this doesn't solve the VT-switching problem.

svgalib

Svgalib will show the same type of problems as the X-server. Some cards will react differently than from XFree86, because they are more or less supported in svgalib.

DOSEMU

Ditto. Only worse. Dosemu only "knows" about some basic VGA cards, but has no knowledgs whatsoever about clock chips and more modern VGA chips. Chances are DOSEMU gets you in text mode trouble.

DOSEMU might not be clever enough to reset all your card's VGA registers (including the clock setting registers) when it starts up in VGA-mode. In that case, any non-standard SVGATextMode mode could produce a non-syncing DOS display. The only cure in this case is to reset to a standard VGA text mode like 80x25 before starting DOSEMU.

A similar problem might pop up when exiting DOSEMU. If it doesn't restore all linux textmode registers, the linux console might get corrupted.

Both problems can be resolved by embedding the DOSEMU call in a script, which does something like this:

	SVGATextMode 80x25x9
	dos
	SVGATextMode My_SuperMode

This will not solve the problem when switching to another virtual terminal while DOSEMU is still running.

DOS

After rebooting to DOS (shame on you! There's a Doom for Linux also) or when starting DOSEMU, the text mode screen, or, more likely some graphics modes might produce a non-syncing display. This is more likely to happen on boards that use a clockchip (i.e. when the TextConfig file has a `ClockChip' line enabled.

The reason for this is that some card's BIOSses don't care to reset all clocks to their defaults when they get a reset signal (i.e. when rebooting). Some die-hard cards won't even do that when you hit the cold-reset switch, and will only revert to the default clock values when you power-cycle the machine.

A simple solution to this is to put an SVGATextMode (or ClockProg) command in the system shutdown script. This is in most cases

	/etc/rc.d/rc.0

If the programmed clock is the correct default clock value, your DOS problems will be solved. The only tricky part here is to find out what that default clock is...

Since SVGATextMode reprograms clock #2 (the third clock) on most clockchips, the default clock value depends on the clockchip type you're using.

Only clocks #0 and #1 are the same for (almost) all VGA chips, and thus this method is only really simple for those clockchips where clock #0 (default = 25.175 MHz) or #1 (28.3 MHz) is reprogrammed. This is currently only for the icd2061a (or the equivalent ics9161) clockchips when the "clockchip_x" option is used.

More Information

Read doc/FAQ in the SVGATextMode distribution for more reading on this subject.

/etc/TextConfig

The (default) configuration file for SVGATextMode

/usr/sbin/SVGATextMode

The main text mode manipulation program described here

SVGATextMode was written by Koen Gadeyne <koen.gadeyne@barco.com>, with help from a lot of local and remote Linux fans.

Much of the VGA code for SVGATextMode was borrowed (I will give it back :-) from the XFree86 3.1 server code (and also from newer versions). The S3 clock chip code and Cirrus Logic clock code was copied (with some improvements added) from the original XFree86 code.

See the CREDITS file in the distribution for a full list of all helping hands.

TextConfig(5) - Configuration file for SVGATextMode

grabmode(8) - A XFree86/SVGATextMode VGA mode grabber

SVGATextMode-x.y/doc/FAQ - description of problems you could encounter when using SVGATextMode, and some solutions.

The 'doc' directory in the SVGATextMode distribution contains a lot of miscellaneous documentation on a range of topics related to configuring and using SVGATextMode.