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BIOS extension for serial console?

Discussion in 'PC Hardware' started by Harald Milz, Dec 10, 2003.

  1. Harald Milz

    Harald Milz Guest

    Hi folks, sorry for the repost but I could not get help in any of the fora
    I've tried so far.

    F'up set to myself, I'll followup accordingly.

    [ This is a repost of the following article: ]
    [ From: Harald Milz <> ]
    [ Subject: BIOS extension for serial console? ]
    [ Newsgroups: comp.lang.asm.x86 ]
    [ Message-ID: <br41mu$isp$> ]


    I have been doing some research on the topic, mainly because I would
    like to add a serial console to my servers running Linux. As soon as
    the boot loader takes over, they provide serial access themselves but I
    would like to be able to fiddle with the BIOS setup or see if a server's
    RAID adapter barfs at his harddisks. We're talking about older legacy
    machines here which can't be upgraded to AMIBIOS8 for example. In my case,
    it's a Tyan S1590S and an Asus A7V.

    Research shows that there appears to be nothing available. Sooooo -
    before I write something myself I would like to get some better idea how
    the most popular BIOSes (AMI, Award/Phoenix) actually boot. This effort
    makes only sense if legacy adapter BIOS extensions at C800 are found
    and initialized very early in the boot process, in particular before
    the BIOS enters the setup screen if requested.

    I am a little bit confused about various sources which I've found. Some
    say, adapter ROMs are found and initialized very early, e.g. before the
    serial ports (!) (like <807hq7$kc1$>#1/1 posted here
    in 1999i). Others like http://www.bioscentral.com/postcodes/awardbios.htm
    say something completely different. And none of them clearly say whether
    it's before or after the entry point for the setup. I would expect that
    all BIOSes use the same or a very similar sequence of events because
    they need to accomodate each and every add-on card with its own BIOS, and
    they can't know if the extension cards need the serial port for example.

    Ideally, I'd like to see everything including the memory check.

    The question is whether a C800 ISA BIOS extension is the Right Thing
    at all. Looking at various BIOS images with CBROM shows that there
    are some more blocks in a compressed BIOS image. Can I add something
    which will be initialized earlier than block C800, directly after the
    VGA BIOS and the serial ports? The "master BIOS" of size 128k (Award)
    seems to be the same in all cases. Modifying the BIOS proper would be
    easy if one had the source code but ... ;-) Yes I know there's LinuxBIOS
    but my boards are not supported by the project, and I don't want to dive
    into the topic _that_ deep.

    Any insight is appreciated...

    Harald Milz, Dec 10, 2003
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  2. Harald Milz

    Robert Myers Guest

    On Wed, 10 Dec 2003 14:58:13 +0000 (UTC), Harald Milz

    Wouldn't any number of KVM technologies available solve your problem
    much more easily than fiddling with the BIOS?

    Robert Myers, Dec 10, 2003
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  3. Harald Milz

    Arno Wagner Guest

    It is a question of bandwidth and cost. Serial can easily
    be converted to TCP/IP with a cheap/old PC or sent over a modem.
    Video/Kbd can be sent over TCP/IP, but the cheapest solutions are
    in the 2000 Euro price range. Cheaper maybe with vga->TV->TV-grabber,
    but what about the keyboard? Modem is out of the question.

    I recently had some similar taks to solve (Linux CLuster), and
    decided to do without remote BIOS access. Now it is KVM switch
    for on-site debugging, booting via etherboot and remote power
    switch for one test machine.

    Arno Wagner, Dec 11, 2003
  4. Harald Milz

    CJT Guest

    That's one thing that makes Sun gear so nice.
    CJT, Dec 11, 2003
  5. Harald Milz

    Robert Myers Guest

    It's also a question of what your time is worth. The card I cited in
    a post that went only to one newsgroup costs about $700US.


    I'm sure VAT would make it significantly higher in Europe, but I don't
    know how much. To get power-on and reset access to an important
    server in a closet somewhere as compared to paying that price, I know
    *I* wouldn't be fiddling ROM code or jury rigging the VGA.

    Robert Myers, Dec 11, 2003
  6. Harald Milz

    Harald Milz Guest

    which is far out of reach for my home network, as is the PC Weasel. AMI and
    Intel have addon cards for that purpose as well but these are also above
    $750. For a customer wanting to revive a legacy machine this may well be
    more than what the machine itself is worth.

    As far as the Startech card is concerned - thanks for the hint, I wasn't
    aware of that. Unfortunately, the only distributor that is active in Europe
    is Ingram Micro, and their web site is a closed dealers' community so that
    I can't check whether they have it over here or not. If not, this is
    not an option for corporate customers due to cross-atlantic support and
    warranty issues.

    And then, a new mainboard which does have serial console support per se
    will be cheaper in many cases. The business case for such a card is flaky
    at best. The PC Weasel at $350 for the PCI version is a borderline case
    as far as price (and there isn't a European distributor either). What
    I intend is a low-cost solution that admittedly will not cover all cases.
    If you can or would use LinuxBIOS, you could use such a solution as well.
    Well that's a matter of taste. Hacking is fun. Otherwise things like
    Unix or Linux would never have existed. :))

    But anyways - I would rather not dive into philosophical discussions. I am
    looking for technical help :)

    While we're at it - I had a look at the BIOS of my Matrox G200 card. In
    DOS DEBUG, I could "d c000:0" or "u c000:3" just fine. But - I could
    not write the block c000:0 32K to a floppy directly using INT 21h,
    AH=40h. Strangely, all that came up were FFh bytes, and 32K of them. I
    could, though, copy the block to another memory location using lodsw,
    stosw, and write it to a floppy from there. Any idea why this is so? I
    mean we're talking about x86 real mode here, and the idea that there
    may be some sort of copy protection seems very weird to me.

    Legacy PCI cards with socketed DIL ROMs are ten a penny on Ebay - many AGP
    cards have socketed PLCC ROMs instead. Which is also fine if you buy or
    make a DIL-PLCC adapter. I'd use EEPROMs for the job because they can be
    reprogrammed without UV erase...

    Without hving looked at other VGA cards - is it safe to assume that their
    BIOS chips are 32K only, and real mode, or do they play dirty tricks like
    compressed images etc.? The card's I've seen on photos have 28pin DIL
    sockets, and the maximum for 28 pins is 1Mx8 (27C801) AFAIK.
    Harald Milz, Dec 11, 2003
  7. Harald Milz

    Robert Myers Guest

    You can't put a dollar (or euro) sign on those rewards. We all have
    different skill sets and time constraints.

    Robert Myers, Dec 11, 2003
  8. The floppy controller is one of the last devices using legacy dma, and the dma
    controller simply cannot access expansion roms on your machine.
    For development a 62256 ram chip would be a better choice. Load it, reset and
    try. If your computer hangs, turn off and on an try again.
    Bios extensions can be up to 64k and start with 55 aa (length/512) on a 2k
    boundary. VGA biosses aren't compressed.

    I've got a Powrtwell comunication appliace which has a bios with a serial
    console. I don't know how they do it - it also works with direct video ram

    Mit freundlichen Grüßen

    Dipl.-Ing. Frank-Christian Krügel
    Frank-Christian Kruegel, Dec 11, 2003
  9. Harald Milz

    Harald Milz Guest

    With a 3V Li cell or so, yes. I've still got some of them left.
    Harald Milz, Dec 14, 2003
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