Linux Cubed Series 3: Developer Tools/Linux Cubed Series 3 - Developer Tools.iso/utils/console/svgatext.9/svgatext/SVGATextCalc.pod

Text File | 1996-06-14 | 6.9 KB | 196 lines

=head1 NAME

SVGATextCalc - SVGATextMode mode calculator

=head1 SYNOPSIS

B<SVGATextCalc>
B<MODE>
[B<--font=fontsize>]
[B<--trick9>]
[B<--verbose>]
[B<--vsf=vertical scanning frequency>]
[B<--dot=Dot clockfrequency (Mhz)>]
[B<--hmargin=horizontal margin factor>]
[B<--vmargin=vertical margin factor>]

=head1 DESCRIPTION

SVGATextCalc takes command line arguments and generates "Modelines" suitable for
SVGATextMode. User supplied arguments are in high-level, understandable formats,
like screen width, height, font size, etc. The program will take this
data and spit out the paraphernalia necessary to (hopefully) program the
VGA registers (this is a task for F<SVGATextMode(1)>).

SVGATextCalc will do its best to make a video mode matching or as close as
possible to the video mode requested by the user. Hardware constraints
(for now, HorizSync and DacSpeed only) will be read from the
SVGATextMode configuration file F</etc/TextConfig>.

SVGATextCalc will do a purely numerical calculation of the horizontal and
vertical VGA parameters and frequencies first. Based on these results,
obvious checks are made (horizontal frequency, dot clock, etc) to see if
they fall within a range compatible with your hardware.  SVGATextCalc will
try really hard to make the best video mode as possible and has some
limited intelligence built in (for instance, it will manipulate the dot
clock frequency if the resulting horizontal frequency falls beyond your
monitor's capability).

Advanced users can control some subtle aspects of the calculations, such
as the Dot clock frequency, vertical scanning frequency and some other
interesting parameters.

=head1 OPTIONS

=over 8

=item B<MODE>

The desired mode. The format is CxR, where C is the number of desired columns and
R is the number of rows.

=item B<--font=fontsize>

Set the font size to be used. VGA hardware fonts are in the form WxH, where W
is Width and H is Height (both in pixels). The default font is 8x16 (used in
the 80x25 mode). Some other common fonts are 8x14, 8x8, etc. See the command
line option B<--trick9> for a discussion about 9 pixel fonts.

=item B<--trick9>

The VGA hardware has a "trick" that allows 9 pixel wide fonts. In fact, they
are the very same 8 point fonts with a space added. This mode has the
advantage of not being so "cluttered" on the screen. If you want this mode,
specify your normal 8 width fonts and add the B<--trick9> command line
option. You must choose an 8 pixel font as you would normally, or
this option will be silently ignored.

=item B<--verbose>

Displays some info to stderr. Nothing else. :)

=item B<--vsf=Vertical scanning frequency (in Hz)>

Set the VSF, also known as vertical refresh rate. The more your monitor can
handle, the better for your eyes. Reduced rates tend to produce flicker.
The default is 60Hz.

=item B<--dot=Dotclock frequency (in MHz)>

Use this to force the program to calculate everything based on the given
Dotclock frequency. Usually, it will be derived from other parameters and
readjusted if the horizontal scanning frequency falls off limits. If you
set the frequency with this option, SVGATextCalc will not attempt to change
it (but you have greater chances of ending with parameters outside the
limits your monitor can handle).

=item B<--hmargin> and B<--vmargin>

These options control internal aspects of the program. If you have the guts
to change them, I suppose you have the guts to take a look at the source
code and discover what you're doing. :)

=head1 ERRORS

The program will make some basic checks against the generated data. Basically,
it will try to avoid overloading your hardware but, of course, computers do
what you tell them to do, not what you want them to do.

=head1 EXAMPLES

=item F<SVGATextCalc 90x30>

I love this one. Fits nicely on my 14" monitor. :)

=item F<SVGATextCalc 90x30 --trick9>

Same as above, but (IMO) much better. Fonts don't "stick" together so much.

=item F<SVGATextCalc 100x37 --font 8x14 --vsf=66>

100 by 37 characters, using an 8x14 font at 66Hz vertical frequency scan.
If you are out of luck (like me) and have a cheap 14" monitor, you'll notice
that the resulting VSF is at 63Hz, not 66Hz as requested. In my case, the
monitor can't handle anything above 35.5Khz (Horizontal scan), so the
program dropped the dotclock frequency a little, trying to keep the
resolution. The result was degraded vertical refresh.

=item F<SVGATextCalc 100x37 --font 8x14 --vsf=66 --dot=38>

Same as above, but forcing the dot clock to 38 MHz. Notice it now sticks to
66 Hz refresh rates with a 36.76KHz horizontal scan rate. That's why it dropped to
63Hz in the previous example (in my case).

=head1 SEE ALSO

F<SVGATextMode(1)>

=head1 WARNINGS

Messing with the VGA registers may damage your hardware. The author (Marco
Paganini, [e-mail]) takes B<NO RESPONSIBILITY> for anything
caused by the use of this program. Every effort has been made to prevent
very stupid mistakes, but always remember that computers are stupid things
and there are many ways to fool a program.

Little story:

Some years ago I was sitting on my office desk, bored as always... All
of a sudden, I remembered a very old monitor we had in spare. The tube
was tainted, the case broken and the circuitry occasionally failed. The
repair would cost more than the monitor itself... I thought then: "Hey,
let's see if this thing can really be burned via software". I grabbed a
small DOS program that allows you to change the VGA registers and set
the frequencies to absurd values. All you could see was a vertical line
in the middle of the screen and a very high pitched noise coming from
the monitor. The noise was loud, but since the intent was to try to burn
the monitor, the louder, the better.

I left it at this state for over 24 hours. Nothing happened. I fiddled
even more with the registers, producing even more obscure results.
Nothing happened.

From that day on, I decided that it's not so easy to burn a monitor
via software. But caution is recommended. The monitor in question was a
Low-end Samsung SyncMaster 3, 35.5Khz/90Hz. I believe that the bigger
monitors may be more sensible to this kind of attack, so watch
carefully what you do.

=back

=head1 BUGS

=over 4

=item *

Not exactly a bug, but there's 90% of a chance that you will have to
use F<vgaset(1)> to tune your video mode. This happens whenever you
generate a new video mode, since it's almost impossible to predict
your monitor timings exactly.

=item *

No check is made for the vertical frequency

=item *

Currently, no individual horizontal frequencies are allowed. It means that
if you use HorizSync A,B,C,D-E,F,G it will only consider the A and F
frequencies as the lower and upper bounds, respectively.

=item *

No space is allowed between the values in the HorizSync line.

=head1 AUTHOR

B<Marco Paganini>
B<[e-mail]>
B<http://www.ism.com.br/~paganini>

If you use this program and find it of any use, please send me your
comments and/or suggestions.

=back