BIOS Autodetection Design

Eric R. Kern eric_kern at
Mon Jan 11 21:45:26 CET 1999

> After alot of thinking about this I've come to the conclusion that I
> that there should be autodetection of chipsets. I have been reading
> pciset documents from Intel, and as Andrew says there is really only
> smaller differences (between the PCI chipsets that is). But all this
> depends on one things; if it is possible to, with 100% accuracy,
> what chipset the BIOS is running on. If this is possible, is see no
> not to include autodetection. A wild guess is that the code for the
> various chipsets (all together) is not more then a couple of kB.

I'll give you a little help with sizing the chipset code since I have
had some experience with this (I am a BIOS programmer for IBM's
Commercial Desktop Division).  Upon bootup of a system, there are many
PCI configuration registers that need to be set to a certain value in
order for the system to boot DOS (let alone a sophisticated operating
system like Linux, Windows NT or Windows 98).  These registers are
generally set through a table early on in POST (Power On Self Test).
The autodetecting BIOS would need to keep a table for every chipset that
it detects.  The tables for all of the chipsets that you want to support
would fill any BIOS EEPROM on the market and you haven't even written
one line of code yet.

I think I have a better design.  There are generally three ways of
modifying the BIOS on a computer.   The first way is to pull the EEPROM
off the mother board and "burn" an image using an EEPROM burner.  The
second way is to enable boot block recovery mode, put the desired flash
image in the floppy drive (or whatever media that was preselected) and
turn the computer on.  (Boot block recovery mode is usually a jumper
setting that runs a "bare bones" portion of BIOS in order to load the
desired image.)  The third way is through a flash utility.

The flash utility should run from DOS (or maybe Linux for you Linux fans
out there).  DOS is used since this utility is run at manufacturing time
before an operating system has been loaded onto the harddrive and DOS
fits nicely onto a floppy.  My proposed design would have the system
boot to a CDROM (more space and everyone has one) which boots DOS.  The
autodetection would be built into the flash utility.  The chipset and
other hardware detected by the flash utility would load the appropriate
modules.  These modules would then be put together to form a BIOS image
and a table of pointers to each module would be created at a specified
location in the image.

+------------------------+ FFFFh
|  Jmp Vector                   |
|  Table of Pointers           |
|  North Bridge Config.    |
|  South Bridge Config.    |
|  Cache Configuration     |
|  Memory Configuration  |
|  ISA Configuration         |
|  PCI Configuration         |
|  Keyboard Controller     |
|  BIOS Functions (int 15)|
|  Planar Hardware           |
|  Etc.                               |
+------------------------+ E000h

Just a thought.  Good luck.

Eric R. Kern

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