[coreboot] Help required to boot DUET (Seabios floppy mechanism)

Scott Duplichan spambucket at notabs.org
Tue Oct 22 21:30:49 CEST 2013

Neo wrote:

]  There has been no response to my thread [Help required to initialize
]coreboot as Seabios (floppy mechanism for DUET) payload] since a long
]time.I have eagerly waited but no solutions have turned up.
]  If Im mistaken in any way or the other please let know.


If this is really something you want I may be able to help. Be aware that
is not an active EDK2 project. Duet has many problems that you must solve
before it is usable. The Duet concept is sound, and is a good match for
But it is not in general a usable project as it exists in the public EDK2

Building Duet should be easy, relative to other EDK2 projects. Can you
build other EDK2 projects? From EFI's beginning in 1999 to recently, the
supported build toolset was Microsoft. Recently gnu build tool support was
But because Duet is not an active project, it may not build easily with gnu
In addition, EDK2 does not properly support any Windows port of the gnu
So try building with Microsoft tools for a reference point. But be aware
that EDK2
actually uses a hard-coded absolute path to the Microsoft tools. So unless
Microsoft build tools are installed in the same location as theirs, you will
have to
modify Basetools\Conf\ tools_def.template.

Once Duet builds, there are some basic bugs to fix. There is a memory
problem for example. Duet cannot work with more than 4GB of RAM if I 
remember correctly. These are all easy to fix. Another problem is a
on the DXE image size. This limitation is due to the DOS 640 KB memory
The DOS 640 KB limit is relevant because the image is read from disk in
mode and low memory is the most convenient place to put it.  This limitation
must be removed before a full featured DXE can be used.

Once all the problems are fixed, the reliance on legacy BIOS INT 13h can
be removed. The image can be kept in flash and then copied to DRAM
instead of reading it from a file.

One of the bigger problems is that UEFI needs a large amount of NVRAM.
The size is too big to fit into CMOS. That means you need to add code to
write this data to flash memory. Normally a 64-KB block of the BIOS flash
chip is set aside for this use.

There are several more problems in addition to these. They can all be
overcome, but it takes some time. The good thing about Duet is that it
uses only the generic portion of UEFI, so it is easy to run on an emulator
such as simnow or qemu for development and debug.

Duet requires that DRAM init and any other chipset initialization be
Duet finds DRAM by calling E820, though passing the info directly is
Duet does not supply ACPI tables. It finds existing ACPI tables and uses
Same for SMBIOS.


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