boot2 -> BTX halted, but loader(8) boots fine

[Anton Shterenlikht]

I'm trying to bootstrap the system using boot2 directly as described
in the Admin Guide (3rd edition, 2004, section 2.3) and in the man
page for boot(8), FreeBSD 6.0, dated 18/08/2005. I have 3 different
kernels. However, no matter which kernel I choose at the boot prompt,
I always get "BTX halted". An example is reporduced below.

-
FreeBSD/i386 boot
Default 0:ad(0,a)/boot/loader
boot: /boot/kernel/kernel
int=00000006  err=00000000  efl=00010002  eip=c0443c30
eax=c0443c30  ebx=c0a273c4  ecx=c0a273c4  edx=a020001e
esi=00000050  edi=c0443c30  ebp=00002275  esp=0009eaf0
cs:eip=ff ff ff ff ff ff ff ff-ff ff ff ff ff ff ff ff
       ff ff ff ff ff ff ff ff-ff ff ff ff ff ff ff ff
ss:esp=69 95 00 00 00 00 00 80-1e 00 20 a0 00 00 00 00
       00 00 00 00 00 00 00 00-a0 dc 00 78 4b 09 00 00
BTX halted

At this point I have to reboot with CTRL+ALT+DEL.

Only values of the following registers(?) change for 3 different kernels:
 eip, eax, ebx, ecx, edi, ebp. However, the values are always identical for
eip, eix, edi and for ebx, ecx. All other values do not change from one
kernel to another.

Bootstrapping with loader(8) works fine, I can load any kernel.

I use FreeBSD 6.0-release on compaq armada 1700 laptop with BIOS
dated 11/30/1999. I cannot find a newer BIOS version for this model.

I've read several reports regarding BTX halted issue on old compaq.
Most people report turing off UDMA or DMA in BIOS as a solution.
I cannot see any DMA settings in my BIOS (I used Compaq Computer
Setup for Portables, ver 2.01H dated 24 Jan 1999). I'm also not sure
if it applies in my case as booting with loader(8) works with no
problems.

How can I learn about the meaning of the registers(?) above?
Do I need to look into the souces for /boot/boot2? 
Am I at all correct in thinking that it is /boot/boot2 that reports BTX halted?

thanks
anton