How to debug BTX loader?

[Darmawan Salihun]

Hi guys, 

I'm currently working on a BIOS for a custom Single Board Computer (SBC). 
I have the required BIOS source code and tools at hand. 
However, the boot process always stuck in the BTX loader 
(the infamous "ACPI autoload failed") when I booted out of USB stick 
(with the FreeBSD 8.1 USB stick image). 

I could get the system to boot into FreeBSD 8.1 
(by keeping the CDROM tray open and close it when the board looks for 
boot device, otherwise BTX will reboot instantly). 

The target development is actually pfsense 2.0 which is based on 
FreeBSD 8.0. I need to know how to make BTX be as "verbose as possible" 
in order to find out what went wrong with the BIOS. I'm suspecting that
 the el-torito support in the BIOS is incomplete. Nonetheless, I need
 hints about debugging the BTX loader to pin point the exact problem(s). 

Anyway, I have fixed the first issue which involves erratic PCI IRQ routing and the board works just fine in Windows XP and Linux 
(Backtrack 3 and CentOS i386). 

I found that FreeBSD boot CD contains this file: boot/defaults/loader.conf 
In order to get verbose BTX output, do I need to set the 'verbose_loading="NO"' to "YES"? 
I'm thinking about "editing" FreeBSD USB stick boot image (how to do that?)

Another thing is, where to find guides about BTX development/debugging 
in order to analyse a crash dump from the BTX? I have been googling for
 one night but doesn't find enough info. I read the FreeBSD developer
 handbook but BTX is not explained in detail there. Where is the location
 of the BTX source code in FreeBSD source code?

That's a lot of questions. Thanks in advance for any response. 

Regards,

Darmawan