Basic Text Mode (was: Re: Question about SysRq)

Basic Text Mode (was: Re: Question about SysRq)

[Thorsten Glaser Geuer]

> Thought, i really love all sysrq properties of linux, so i need less often
> to make hardware resets an then await and fear, what fsck will print.

101% ACK

> One more property, that i'd like to have should be request key to force the
> most basic text mode (say 80x25) on the console, when eg. X freezes and 
> i kill its session, then last gfx mode resides on the screen and see no way 
> to restore back the text mode - /usr/bin/reset or something alike will not 
> do it. But it seems to be not a good idea at all, does it ? 

It is a very good idea, and to implement quite easy. You just do have to
diff between three types of video cards (MDA, MGA and HGC vs. CGA and AGA vs. EGA+).
Then you do direct register writes. For the HGC I did it recently in a DOS proggy
which switched from text to gfx and back. I had a TSR which simulated a gfx BIOS.
Only problem is, I lost the source. But I could rewrite and test it on request.
I even would put it under GPL for the kernel (normally this is a no-no for me),
just ask me. I will write it in NASM then because I can't the AT&T syntax.
For non-i386 Platforms I do not know about this topic. (IIRC the Apples didnt
even have a text mode)
Maybe I could look up the EGA register values somewhere.

-mirabilos

Re: Basic Text Mode (was: Re: Question about SysRq)

[James Simmons]

> One more property, that i'd like to have should be request key to force
> the most basic text mode (say 80x25) on the console, when eg. X freezes
> and i kill its session, then last gfx mode resides on the screen and
> see no way to restore back the text mode - /usr/bin/reset or something
> alike will not do it. But it seems to be not a good idea at all, does it
> ?

I'm working on this. In theory it should be possible with SAK. Alt-SysRq-k
resets the console. Here it set the vc_mode back to KD_TEXT and the
keyboard back to VC_XLATE. It even reset ths palette. What it doesn't do
is reset the hardware state. I hope to change this for 2.5.X. It is
possible using fbdev to do this very easily. I'm working on it so you can
go back and forth between fbdev and vgacon for those who want to if their
hardware supports it use vgacon. This can be applied to this problem very
easily.

MS: (n) 1. A debilitating and surprisingly widespread affliction that
renders the sufferer barely able to perform the simplest task. 2. A disease.

James Simmons  [jsimmons@linux-fbdev.org]               ____/|
fbdev/console/gfx developer                             \ o.O|
http://www.linux-fbdev.org                               =(_)=
http://linuxgfx.sourceforge.net                            U
http://linuxconsole.sourceforge.net

Re: Basic Text Mode (was: Re: Question about SysRq)

[Boris Pisarcik]

> It is a very good idea, and to implement quite easy. You just do have to
> diff between three types of video cards (MDA, MGA and HGC vs. CGA and AGA vs. EGA+).
> Then you do direct register writes. For the HGC I did it recently in a DOS proggy
> which switched from text to gfx and back. I had a TSR which simulated a gfx BIOS.
> Only problem is, I lost the source. But I could rewrite and test it on request.
> I even would put it under GPL for the kernel (normally this is a no-no for me),
> just ask me. I will write it in NASM then because I can't the AT&T syntax.
> For non-i386 Platforms I do not know about this topic. (IIRC the Apples didnt
> even have a text mode)
> Maybe I could look up the EGA register values somewhere.

The hardware part of mode restoring could really be done the register way and
may be interesting - i did code a lot in dos and this is what i did too, 
if i had experience with register programming and vga(..). Mostly i skipped
this arena, because i have had information about vga registers just enough
to damage monitor, so rather used VESA for video stuff :)
But i think only this way should break some internal state of console or
what driver. 

Thanks for the willingness, thought. I read from the thread - James Simmons,
console developer, is working on it, so you may eg. ask to cooperate with him,
he surely has a lot of ideas of text/vga switching in linux.

Cheers                                                               B.

Re: Basic Text Mode (was: Re: Question about SysRq)

[Boris Pisarcik]

Some stupid questions about videomem:

1) How do 2 or more X servers, or svgalibbed apps share the same physical video
memory ? Does it get saved to ram when switching between them ? 

2) Does console switching (gfx or text) save and restore all registers of
videocard in kernel ? Or kernel only restores text things and gfx apps must
it do in their own ?