Re: [9fans] What a poor VGA support !

[Agnelo de la Crotche <agnelo.geo@yahoo.com>]

presotto@plan9.bell-labs.com wrote:

> > Simple, because it is supported by the 28 other
> > operating systems I managed to install on that machine.
>
> My interest is clearly piqued.  What are those 28 OS's and
> what to you use to boot them all?
>

As long as you're asking 'how?' and not 'why?' ....

- 6 DOSez : MS-DOS, PC DOS, Open DOS, DR DOS,  PTS DOS, Free DOS
    - 6 Windozes : 95, 98 , ME, NT, 2K, XP
    - 3 BSD : Free BSD, Open BSD, Net BSD
    - 2 Linux : Debian, Suse
    - 2 Unix : SCO, Solaris
    - 1 Minix
    - 8 others : Hurd, BeOS, QNX, OS/2, AtheOS, VsTa, Netware, Amoeba
    - 1 Plan9

on 2 IBM IDE 40 GB harddisks,  a single AMD K6-2 500 MHz CPU and 512 MB Ram.

Basically I use 3 bootmanagers :
    - xfdisk ( http://www.mecronome.de/xfdisk/ ) in the MBR of the first HD
    - the XP bootloader in the bootsector of a primary FAt 16 partition ( <=
256 MB )
    - Grub in a bootsector of some logical partition.

    and some small shell scripts and batchfiles calling utilities (like dd)
to rewrite
    the partition tables when necessary.

As a rule, I never use a floppy, emulator or virtual machine. If I cannot
boot an
operating system the simple way from the harddisk, I don't install it.

It is not as complicated  as writing video drivers and probably much more
useless, but
having spent the last couple years playing around with bootsectors, hard disk

partitions and 'ennemy' operating systems, I would probably have enough stuff
to
dedicate a website to the subject, although there are already plenty of
those, but
I've never heard of anybody getting as many bootable OS.  The only problem is

that I need at least  3 hours of sleep.

You can easily figure out that the greatest difficulty has been to get the
widest compatible
hardware components for all these OS.   Replacing a video card is a great big
deal
for me.


>
> > But , please, tell me, because I'm curious : Why is it so difficult, so
> > impossible to add some kind of minimum VGA support  ?
>
> We used to have minimum support, i.e., 640x480x{1,2,4}.  Those modes are
> standard and normally grey scale.  You can use a color map with them
> but 16 or fewer colors doesn't make for great viewing, red letters on
> a blue backround was my favorite headache producer.
>

Even under DOS I can get some graphic based applications working
in a reasonnable resolution. ( which doesn't mean that I use them !)

>
> We nuked support for the standard modes because
> a) it was very odd to implement especially after we changed
>   graphics models.  It doesn't really fit the
>   model of a frame buffer.  Instead you had to do odd things
>   to write the different bits to diferent planes.
> b) it was made clear to us that supporting 640x480x4 grey scale
>   was so inferior to what people wanted that it wasn't worth the
>   effort.
>
> All other modes are non-standard, i.e., different from card type
> to card type.  There are a smaller number of VGA chips than cards
> though even that number is unwieldy.  How the differenty
> card manufacturers map the chips and plug them together varies.
> Often the only extra info we have to know about a card is how to
> recognize it.  PCI is helping there though in the past we had to
> look at the onboard BIOS and look for patterns; half of /lib/vgadb
> is just trying to figure out what's there.  If you wc /sys/src/cmd/aux/vga
> you'll see that the ammount of code per chip type is pretty small
> (often with an equivalent amount in the kernel to support
> cursors and such).  However figuring out that code is hard:
>

I've already tried, read, compared, posted, modified all that ( without
knowing what
I was doing ) last year, with the only result of destroying a monitor.  I'm
not
complaining about that, I was aware of the risk.


>
> - documentation is usually poor or non-existant.  Drivers from
>  more popular OS's (or X) are often the only documentation
> - Some registers bits lock out other registers; just reading the
>  settings used by windows and rewriting them back is usually
>  impossible.
> - setup requires writing values into MANY registers, most of
>  which are different from chip to chip.  The values are dependent
>  on clock speed, bit depth, screen size, and chip version.  Just
>  getting them working on one machine doesn't ensure they'll work
>  on another.  In some cases it takes futzing with a number of
>  machines and board revs to get a `stable' implementation.

What I found particularly annoying and frustrating is that it almost works.
Almost !  I have already discussed that issue and probalby other people
did as well.  You know : the problem with the overlapped screen !
The chipset is identified,  because different ATI Xpert use the same
chipset and so have the same BIOS signature. I was told that they run at
different clock speed.
Even if what I got to  see, about 2/3 of  windows is sufficient for the
installation,
you cannot think of starting anything  with it.


>
> Our most popular laptop is the T23 (because of a company deal with
> IBM) and we set it up by being careful not to touch too many registers
> since we have no idea what the LCD extension registers do.
>
> In our group, we have one person, jmk, who sepnds a considerable amount
> of time just getting the cards we have working.  However, that's
> in addition to what he's supposed to be doing, not what he's paid
> for.  Some of the community is also nice enough to send us the /lib/vgadb
> info + drivers to get other cards working.

So did I.


>  However, because the
> Plan 9 distribution is a 'free time' effort at the Labs we can't
> aim one person to doing full time VGA support.  If the community
> were larger, we'ld probably get enough contributions to cover a
> larger percentage of the cards or if Plan 9 were actually popular
> we might be able to get manufacturers to write drivers.
>
> It would be useful if the manufacturers could get together and
> come up with another VGA standard so that we would waste less
> time and angst.  However, there's no real motivation for this.
> To first order, there's only one OS for PC's, and to second order
> only two.  It's not that hard for a manufacturer to put together
> drivers for their new board for 2 OS's.

Obviously if they were humanists, they won't be manufacturers.


>  I'm pretty impressed that
> there are 26 others that manage to support all cards.

As I said Plan9 is the 'only' OS which doesn't work like it should.
I've been coming so far with that operating system to write a
bootmenu and set the default to 'no vga'. So at least, it boots
and opens a console and I can count it as the 29th.

>

> Besides, if you ever got your ATI Xpert (Rage Pro) working,
> we'ld have to go through this conversation again explaining why
> we don't have a web browser worth using.

Since I (almost) never get up, I keep trying regurarly ...

agnelo.