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SeaBIOS (previously known as LegacyBIOS) is an open-source legacy BIOS implementation, which can also be used as coreboot payload.
Any software requiring 16-bit BIOS services benefits from SeaBIOS.
Windows XP has been booted on real hardware with coreboot and SeaBIOS. Some patches are required.
Windows Vista (64/32 bit) has been booted on real hardware with coreboot and SeaBIOS. Some patches are required.
Windows 7 Beta
Windows 7 Beta (64 bit) has been booted on real hardware with coreboot and SeaBIOS. Only obstacle is Coreboot ACPI support. So far K8M890/AMD64 is known to work.
GRUB works with coreboot and SeaBIOS on real hardware and boots Linux just fine.
You can download the latest version of SeaBIOS through a git repository:
<source lang="bash"> $ git clone git://git.linuxtogo.org/home/kevin/seabios.git seabios $ cd seabios </source>
Edit src/config.h and set the following values:
- define CONFIG_COREBOOT 1
- define CONFIG_DEBUG_SERIAL 1
- define CONFIG_OPTIONROMS_DEPLOYED 0
- define CONFIG_COREBOOT_FLASH 1
- define CONFIG_VGAHOOKS 1
<source lang="bash"> $ make </source>
The final SeaBIOS payload file is out/bios.bin.elf, which can be used with coreboot v2 or v3.
For best results, use coreboot-v2 and edit the target Config.lb with the following:
option CONFIG_CBFS=1 option HAVE_HIGH_TABLES=1 ... romimage "fallback" ... payload /path/to/seabios/out/bios.bin.elf end
Unfortunately, many boards don't have HAVE_HIGH_TABLES support yet. If the build fails complaining about this option, one can edit the src/mainboard/<vendor>/<board>/Options.lb file and add a "uses HAVE_HIGH_TABLES" line. Then one can edit src/arch/i386/boot/tables.c and change the lines:
<source lang="C"> uint64_t high_tables_base = 0; uint64_t high_tables_size; </source>
<source lang="C"> uint64_t high_tables_base = ( <memorysize> )*1024*1024 - (64*1024); uint64_t high_tables_size = 64*1024; </source>
where <memorysize> is the amount of memory (in MiB) available on the target machine, but not more than 3072. So, if you have more than 3GiB of ram installed, put 3072. Otherwise, put the number of MiB of ram installed in your machine.
Alternatively, one can add proper support for HAVE_HIGH_TABLES.
Once the above is done, the final image will be in coreboot.rom.
SeaBIOS and CBFS
SeaBIOS can read the coreboot flash filesystem and extract option roms and payloads.
When SeaBIOS scans the target machine's PCI devices, it will recognize option roms in CBFS that have the form "pciVVVV,DDDD.rom". It will also run any file in the directory "genroms/" as an option rom not specific to a device. In the above cases, SeaBIOS will recognize files with a ".lzma" suffix, and automatically decompress them (eg, "pci1106,3344.rom.lzma" and "genroms/sgabios.bin.lzma").
SeaBIOS will also load payloads found in the CBFS directory "img/".
The examples below show some common uses of this feature.
Adding a VGA option rom
It is frequently necessary to add a vga option rom for built-in VGA adapters so that they are properly initialized.
The first step is to find the vendor and device id of the VGA adapter. This information can be found from lspci:
<source lang="bash"> $ lspci -vnn ... 01:00.0 VGA compatible controller : VIA Technologies, Inc. UniChrome Pro IGP [1106:3344] (rev 01) (prog-if 00 [VGA controller]) </source>
In the above example, the VGA vendor/deviceid is "1106:3344". Obtain the vga rom (eg, vgabios.bin) and add it to the rom with:
<source lang="bash"> $ ./cbfstool coreboot.rom add /path/to/vgabios.bin pci1106,3344.rom 0 $ ./cbfstool coreboot.rom print </source>
Alternatively, SeaBIOS supports lzma compressed option roms. Use the following to add a compressed option rom instead:
<source lang="bash"> $ lzma -zc /path/to/vgabios.bin > vgabios.bin.lzma $ ./cbfstool coreboot.rom add vgabios.bin.lzma pci1106,3344.rom.lzma 0 $ ./cbfstool coreboot.rom print </source>
After the above is done, one can write the coreboot.rom file to flash. SeaBIOS will extract the vga rom and run it during boot.
Adding gpxe support
A [gpxe] option rom can nicely complement SeaBIOS and coreboot by adding network boot support. Adding gpxe is similar to #Adding a VGA option rom. The first step is to find the ethernet vendor/device id. For example:
<source lang="bash"> $ lspci -vnn ... 00:09.0 Ethernet controller : Realtek Semiconductor Co., Ltd. RTL-8110SC/8169SC Gigabit Ethernet [10ec:8167] (rev 10) </source>
Then one can build a gpxe option rom. For example:
<source lang="bash"> $ cd /path/to/gpxe/src/ $ make bin/10ec8167.rom </source>
And add it to the coreboot image. For example:
<source lang="bash"> $ ./cbfstool coreboot.rom add /path/to/gpxe/src/bin/10ec8167.rom pci10ec,8167.rom 0 $ ./cbfstool coreboot.rom print </source>
As with VGA option roms, the gpxe option rom may be compressed with lzma. However, compression wont significantly reduce gpxe's size as it implements its own compression.
In addition to gpxe, other option roms can be added in the same manor.
Adding sgabios support
An [sgabios] option rom can forward some vga bios requests over a serial port. To use sgabios, place its rom file in the "genroms/" directory of CBFS. For example:
<source lang="bash"> $ ./cbfstool coreboot.rom add /path/to/sgabios.bin genroms/sgabios.bin 0 $ ./cbfstool coreboot.rom print </source>
Most payloads can also be launched from SeaBIOS. To add a payload, build the corresponding .elf file and then add it to the coreboot.rom file in the "img/" directory. For example:
<source lang="bash"> $ ./cbfstool coreboot.rom add-payload /path/to/payload.elf img/MyPayload l $ ./cbfstool coreboot.rom print </source>
During boot, one can press the F12 key to get a boot menu. SeaBIOS will show all files in the "img/" directory, and one can instruct SeaBIOS to run them.
Note, SeaBIOS currently supports uncompressed and lzma compressed payloads. The nrv2b compression algorithm is not supported.