Linux-kernel mailing list archive 1999-22,: Re: vgacon & mdacon hercules related question

# Re: vgacon & mdacon hercules related question

Martin Mares (mj@ucw.cz)
Mon, 31 May 1999 12:12:26 +0200

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Hi,

> We're using a pentium based PC with hercules monochrome monitor&card at
> home running Linux. The main disadvantage of this combination is the missing
> scroll back function. Since hercules is an ISA card there're also problems
> with scolling VTs (produces strange noise when playing something through
> an isa based sound card). BUT hercules supports hardware scrolling as wall
> as VGA. drivers/video/vgacon.c can handle MDA console as well but it doesn't
> know anything about hercules. So first I must detect hercules. Then I realized
> that in mdacon.c there're the right routines ! And NOW, what's up ?
> Should I put the SAME code into vgacon.c which is existed in mdacon.c ?

The problem is that the video memory size detection routines in mdacon.c
are not 100% reliable. I've already seen several bug reports on this and it
seems we'll have to add a optional parameter to override the size. I want
vgacon (being the default console driver on PC's) to work perfectly with
all cards, even if it means scrollback being unsupported on the HGC.

Anyway, we might try adding a command-line option for specifying the
size manually or just detect HGC and assume minimum memory size possible
for a HGC. This (and setting vga_hardscroll_enable to 1) should be enough
to get a working hardware scrolling and scrollback.

> The best thing would be separated mda and vga console code but it has
> got one big disadvantage : kernel compiled to VGA console won't run
> on hercules and vice versa. I think there should be a cleaning about
> mda & vga console handling ... Also interesing things about dual heading
> system (VGA/Hercules). Maybe we should have only ONE driver for mda (and
> hercules too) / VGA with capability to handle multiple output (like VGA
> and MDA) ?

Current situation is:

o vgacon supports MDA, HGC, EGA and VGA cards, but can be
loaded only once.
o mdacon supports MDA/HGC as a secondary display, but it can be
also configured to take over the videocard and replace vgacon.

It would be nice to have one driver which could be loaded multiple
times, but it isn't trivial to implement.

> Another question : is there way to reduce the effect to sound playing of
> hercules displaying (for example using XF86_MONO ...) or this is the effect
> of the famous "excellent" PC architecture ?

It's probably because of poor shielding of the sound card :-(

Have a nice fortnight

    --
    Martin `MJ' Mares   <mj@ucw.cz>   http://atrey.karlin.mff.cuni.cz/~mj/
    Faculty of Math and Physics, Charles University, Prague, Czech Rep., Earth
    "And God said: E = 1/2mv^2 - Ze^2/r ...and there *WAS* light!"

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