Date: Sat, 07 Sep 1996 14:04:48 +0200 From: Arve Ronning <Arve.Ronning@alcatel.no> To: J Wunsch <j@uriah.heep.sax.de> Cc: arver@sn.no, freebsd-hackers@freebsd.org Subject: Re: Support for fixed-scan monitors Message-ID: <323164E0.41C67EA6@alcatel.no> References: <199609061814.UAA05394@uriah.heep.sax.de>
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J Wunsch wrote:
>
> As Arve Ronning wrote:
>
> > I've been thinking about submitting my patches to FreeBSD.org. The new code
> > would be hidden behind an 'option PREFER_MDA'. But as one of the changes is
> > in the boot-blocks I think this will be a problem because kernel-config
> > options aren't visible when making the boot-blocks (I'm on thin ice here,
> > please feel free to give some advice:).
>
> This is tricky and in the same boat as the ``FORCE_COMCONSOLE'' stuff
> that is already in the bootstrap. Probing would be more ideal, but
> 7.5 KB are not plenty of space.
>
Ok, I'll have a look at the 'FORCE_COMCONSOLE' stuff.
>From my old files I can see that I first did the 'PREFER_MDA' thing in jan.96
and it has worked ok with three different BIOSes/motherboards.
What it does is this : (compared to the stock version)
in start.S : old new
use whatever BIOS #ifdef PREFER_MDA
is using; if (BIOS is using MDA) /*do nothing*/;
else if (MDA present) { /* 'probe' ! */
'trick' BIOS into using MDA;
}
#endif
use whatever BIOS is using;
in syscons.c, scinit() :
old new
if (!(VGA present)) #ifdef PREFER_MDA
use MDA; if (MDA present)
else use MDA;
use VGA; else
use VGA;
#else
if (!(VGA present))
use MDA;
else
use VGA;
#endif
The (MDA present) and (VGA present) 'probes' are simple write-something-and-
check-if-it-can-be-read-back (like the original in scinit()).
What this is all meant to achieve is :
1) if PREFER_MDA is *not* defined, the code is unchanged.
2) if PREFER_MDA is defined and only MDA present, MDA is used.
3) if PREFER_MDA is defined and both MDA and VGA present, MDA is used.
4) if PREFER_MDA is defined and only VGA is present, VGA is used.
So, in effect PREFER_MDA does what it says : PREFER MDA over VGA, while the
original code does PREFER VGA over MDA.
(And the point to all this is that my large cheap fixed-scan monitor can be
used for X while the MDA monitor is used for booting and starting X:).
Would you be interested in looking at the patches and give me your opinion ?
Do you think there would be any interest in including this in -current ? (or
any other version for that matter:).
Regards Arve
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