Re: Boot (i386) hangs in absence of video hardware

[Martin Husemann <martin%duskware.de@localhost>]

On Fri, Mar 04, 2011 at 02:04:56PM -0700, Scrap Happy wrote:
> I would prefer to understand what the problem really *is*
> than to go flailing at possible fixes.  I.e., knowing
> how the kernel is talking *to* the hardware at various
> stages of the process (since the boot process begins AS IF
> the console has already been redirected to the serial port;
> so, how orderly will the handoff -- BIOS to kernel -- be
> when/if it happens?).  Otherwise, I'll just waste time
> getting back to exactly the same problem...  :<

Well, as you describe it, it looks like this:

 - BIOS emulates the vga (int 10) output functions by talking to the
   serial console
 - the bootloader only uses bios calls to do input/output
 - bootloader loads kernel (output works so far), then passes console
   device used, disk where it loaded the kernel from, etc., to the kernel
 - kernel takes over and imediately talks directly to hardware - assuming,
   as it has been told by the bootloader, that there is a functional vga
   device

Now the problem with "consdev com0" could either be serial port
parameters, or the bios not allowing access to com0 - as it is busy
with the vga emulation.

My bet would be: once you get the bootloader to pass "console is com0 at
speed ...." to the kernel, everything should work fine. A pretty common
hardware with similar bios emulation is the Soekris stuff, maybe you can
find some hints in the mailing list archives googling for that.

Martin