Re: [Etherboot-developers] AoE - questions needing answers

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On Tue, Dec 13, 2005 at 08:31:57PM +1100, James Harper wrote:
> I think I've now got a vague grasp on the asm code and the concepts of
> 16 bit mode and 32 bit protected mode, but need some more information...
> 
> Ideally, imho, the AoE code would replace the ROM on an existing network
> adapter and turn it into an AoE initiator as far as the boot process is
> concerned. I have an intel gigabit card with a boot rom on it, and the
> boot rom can configure a few things, like how long to present the 'press
> ctrl-S to configure' message for, etc, which indicates some extra
> configuration space which could be used for AoE specific config... Or
> maybe it is using a block of flash for that...
> 
> It might be nice if the individual network code could provide a routine
> to store and retrieve configuration data, but I fear that that sort of
> stuff is not chipset specific but rather implementation specific (eg
> three different cards with an eepro100 chipset might be completely
> different in all other respects).
> 
> Anyway, the boot process on x86 should look like:
> Rom Init:
> . Do the copy to ram and setup 32 bit stuff*
> . Display some version information.
> . Probe C: (and D:?) and display details on screen.

(c:  those smileys, are that local hardisks?  :-D)

> . Prompt user for key combination to enter configuration screen
> . Clean up allocated ram and 32 bit stuff*
> . Legacy: Assuming that the AoE initiator is to be active, install a
> handler for int19 to start the boot
> . PNP/PCI: Assuming that the AoE initiator is to be active, return to
> the BIOS indicating that we can be booted from
> 
> Config Menu Options:
> . Enable/Disable

  . Be "Disk" or "Disk Controller"   (or "both"? )

> . Show all AoE targets found on the network
> . Select targets for C: and D:
> . Configure geometry/translation (defaults will be provided based on
> standard translations)
> 
> Boot:
> . Install int13 handler in memory and protect so it won't be
> overwritten*
> . Do the normal boot stuff (load the first sector of C: into memory and
> boot it)
> 
> * I'm a bit vague on why the 32 bit code needs to be allocated to such a
> high area of memory, and once there, how to stop it being overwritten by
> something else. Why couldn't the rom be not compressed, and copied to
> ram which is then mapped over the rom, at the same address? In 32 bit
> mode, we can pretend the virtual address is anything without worrying
> about the physical address yes? Or is this too system dependant? Or does
> going from a 32k rom to a 64k rom make this too hard?
> 
> With the code I've got, GRUB loads the kernel and initrd, but then
> crashes. My best guess is that GRUB tries to issue an int13h reset as
> the last thing it does once the operating system is loaded into memory,
> before jumping into the operating system. But at the time this happens,
> my int13 aoe code has been clobbered. I haven't yet had a close enough
> look to see if this is the case though. How does the PXE EXPORT code get
> around this?
> 
> Any and all information you can give me will be much appreciated!

I think it is a cool project, but I'm allready occupied by other stuff.
At http://wiki.etherboot.org/pmwiki.php/Main/AoE is a pointer to this
thread, so I hope that it gets more momentum.


> Thanks
> 
> James

HTH
GSt
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