[gPXE-devel] About !PXE and UNDI_LOADER

[Glenn Brown]

Sean,

I wonder:

Since you say "our OS" it sounds like you are writing your own OS.
If so, I expect you might work around the BIOS not loading and 
initializing the gPXE ROM by having the OS do it.  Specifically:
	Scan the PCI bus for Ethernet network devices with
	PCI expansion ROMs.
	Scan the PCI expansion ROM chain for the ROM compatible
	with your architecture.
	Copy the ROM into low memory allocated from the BIOS.
	Call the ROM's POST entry point.
I believe that would register PXE and UNDI, assuming the BIOS still
provides the necessary PCI access and low memory allocation support 
required by gPXE.

If your OS runs in 32-bit or 64-bit mode, using 16-bit PXE/UNDI must be 
horribly complex.  However, I believe gPXE can provide an EFI SNP 
interface over PXE, possibly hiding the complexity, and providing a 
64-bit interface that can be used on 32-bit and 64-bit systems.  So, if 
you make your OS expect the EFI SNP interface, then you may be able to 
layer the OS over both PXE/UNDI via a gPXE shim, or over native EFI drivers.

It's quite possible, even likely, that I'm wrong somewhere, since I'm no 
expert on preboot environments or on the internals of gPXE's EFI 
implementation, but I expect others will correct me where I'm wrong.

--Glenn