debug x86 custom OS

[HaQue <admin () smartwave-wireless com>]

Hi all,

Long time listener, first time caller.

The hint to post here came from Intern Mikes great talk at B-Sides.

I am hoping that someone here can give me some pointers on how to 
debug/monitor a custom OS that runs on a standard Intel mainboard.  
Basically it boots up and used the hardware directly, the Intel chipset 
and integrated video. Doesn't run on DOS, windows or Linux, is not a 
Linux or DOS "derivative or clone.  It does use hardware interrupts, and 
I believe BIOS routines.

Obviously this means custom drivers and executables (which are very 
few).

IDA sees the driver files as "MS-DOS SYS-file(perhaps device 
driver)[dos.ldw]" and I get some coherent code mentioning interrupts, 
such as Strategy_Routine, Interrupt_Routine but nothing to really speak 
of.

I Initially thought to hook up to the serial port and monitor with 
another PC, similar to what you would do in an embedded system, though 
quickly realised that this output of dmesg Is programmed into Linux, and 
no such functionality exists in my case.

Short of JTAG on the CPU or video, is there anything anyone could 
suggest to figure out the routines?

Is there anything on a standard Intel PC motherboard that can help?

All the embedded hardware hacking I have done doesn't seem to transfer 
to this, and though ripping apart the software is kind of helpful to see 
the overall picture of how the system works, I don't see how to use the 
info to interact with the OS aside from the basic, intended 
functionality.

Any tips or links to sites that may help would be great.

Cheers,

HaQue

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