[openfirmware] Making Open Firmware look like CE

[Mitch Bradley]

On 5/28/2011 2:19 AM, Mark Morgan Lloyd wrote:
> A few weeks ago (mid March) I mentioned that I had some ARM boards that
> I'd like use as Linux development systems. Unfortunately, they come with
> CE, and while the manufacturer does supply Linux it's prohibitively
> expensive.
>
> CE is booted from a partitioned CompactFlash card, and I initially
> thought that the code in the partition and filesystem boot sectors was
> relevant, i.e. that there was something equivalent to a PC's BIOS in
> Flash. However on inspection I think that the code is x86, which implies
> that the loader in Flash is reading and transferring control to the OS
> image directly.
>
> Is it possible to build Open Firmware to look like a CE image, which
> would possibly allow this board (and potentially many other devices) to
> run Linux without modification to the content of internal Flash?
>

It should be relatively easy.  The ARM version of OFW is dynamically 
relocatable, so all you have to do is put it somewhere in memory and 
jump to it.

I believe that WinCE use the PECOFF image format, documented at 
http://msdn.microsoft.com/en-us/windows/hardware/gg463125

There is also /usr/include/linux/coff.h which may clarify some things.

PECOFF has a lot of features but I think all you need is file header 
followed by a single section header.  My best guess is that the section 
name should be ".text".  The physical address and virtual address should 
be the desired load address (which is pretty flexible as I mentioned), 
and the file pointer would be the offset to the OFW image data.

This is the sort of thing - slapping on random headers as required by 
some pre-existing bootloader - that I do routinely when porting to a new 
platform.

The thing to do is to hex dump the first thousand bytes of the CE image 
and see if you can make sense of it as a PECOFF header.  Then put a 
similar header on the front of the OFW image.

cpu/arm/savefort.fth contains an example of making a header (in this 
case in AIF - ARM Image Format) then writing the header and the OFW 
dictionary image out to a file.