[syslinux] "pre-OS"

[H. Peter Anvin]

Josh Lehan wrote:
> 
> I'm thinking along the lines of a tool that would go out and 
> auto-discover various devices connected via USB, FireWire, etc. and then 
> set up a BIOS "driver" to support INT 13 access to them.
> 

This certainly is more than possible; it's a big job however.  An 
example of this kind of stuff is actually MEMDISK, which creates a disk 
interface for a chunk of RAM.

At least the number of USB and Firewire interfaces has stabilized (USB 
is UHCI/OHCI/EHCI, and Firewire is OHCI1394).

The biggest challenge is that the code has to be small, and written as 
true 16-bit code if you want it to be universal.  Even touching high 
memory *at all* is problematic, as evidenced by MEMDISK.  You have 640K 
of RAM to play with, and the OS loader will want some part of that -- 
how much, exactly, is OS loader dependent.  SYSLINUX, for example, uses 
up to 320K; a PXE stack can be ~150K, etc.  If you care about DOS; DOS 
programs tend to want as much of the low 640K as it can get.

	-hpa