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SeaBIOS is an open-source legacy BIOS implementation which can be used as a coreboot payload. It implements the standard BIOS calling interfaces that a typical x86 proprietary BIOS implements.
This page describes using SeaBIOS with coreboot. SeaBIOS can also run natively in QEMU and bochs — see the SeaBIOS website for information on non-coreboot uses.
Any software requiring 16-bit BIOS services benefits from SeaBIOS (eg, Windows and DOS). SeaBIOS also enables booting Linux out of the box (using standard boot-loaders like GRUB and Syslinux).
SeaBIOS supports booting from ATA hard drives, ATAPI CDROMs, USB hard drives, USB CDROMs, payloads in flash, and from Option ROMs (eg, SCSI or network cards). SeaBIOS can initialize and use a PS/2 keyboard or USB keyboard.
SeaBIOS has been tested with Windows XP, Windows 2008, Windows Vista (64/32 bit), Windows 7 (32 bit and 64 bit).
However, Windows has a very strict ACPI interpreter, and some coreboot boards do not have a complete ACPI definition. As a result, some coreboot boards may fail during Windows boot (eg, it may fail with a STOP 0xA5 code).
Many boards do have working ACPI and are able to boot XP/Vista/Windows 7. Please check the board documentation or ask on the mailing list if unsure of the status.
SeaBIOS has been tested with GRUB, LILO, and Syslinux. Linux booting works well.
SeaBIOS has also been tested with FreeDOS, NetBSD, and OpenBSD.
Because SeaBIOS implements the standard x86 BIOS interfaces, it is expected many other operating systems and boot-loaders will work.
Probably the easiest way to use SeaBIOS as coreboot payload is to simply use the coreboot build process, which downloads and builds SeaBIOS as payload by default nowadays. You just have to run the following in your coreboot checkout:
<source lang="bash"> $ make menuconfig $ make </source>
Both SeaBIOS and coreboot will be built, and SeaBIOS will be added as payload to the coreboot.rom image that is being built.
One can download the latest version of SeaBIOS through a git repository:
<source lang="bash"> $ git clone git://git.seabios.org/seabios.git seabios $ cd seabios </source>
There's also a cgit facility to browse the latest source code online.
Run make menuconfig and set the following variables:
- CONFIG_COREBOOT 1
- CONFIG_DEBUG_SERIAL 1
<source lang="bash"> $ make </source>
The final SeaBIOS payload file is out/bios.bin.elf.
Configure coreboot with the following all disabled: CONFIG_VGA_ROM_RUN, CONFIG_PCI_ROM_RUN, CONFIG_ON_DEVICE_ROM_RUN
Then configure the SeaBIOS out/bios.bin.elf file as the coreboot payload and build coreboot. The resulting coreboot.rom file will contain both SeaBIOS and coreboot, and it can be flashed to a ROM chip.
SeaBIOS and CBFS
SeaBIOS can read the coreboot flash filesystem and extract files. Details on the CBFS files that SeaBIOS supports are on the SeaBIOS wiki.
The following examples show some commonly used features.
Adding a VGA option ROM
It is frequently necessary to add a VGA option ROM to CBFS in order to use a VGA adapter that is built-in to a motherboard. Note, VGA adapters on external cards (PCI, AGP, PCIe) do not require this step as SeaBIOS will automatically extract the VGA BIOS directly from the card. For machines without a VGA adapter, please follow the sgabios instructions below.
Using your BIOS's VGA option rom
The first step is to find the vendor and device ID of the built-in 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/device ID is 1106:3344. Obtain the VGA ROM (eg, vgabios.bin) and add it to the ROM with:
<source lang="bash"> $ ./build/cbfstool build/coreboot.rom add -f /path/to/vgabios.bin -n pci1106,3344.rom -t optionrom $ ./build/cbfstool build/coreboot.rom print </source>
Alternatively, SeaBIOS supports LZMA compressed option ROMs. Use the following to add a compressed option ROM instead:
<source lang="bash"> $ ./build/cbfstool build/coreboot.rom add -f /path/to/vgabios.bin -c lzma -n pci1106,3344.rom.lzma -t optionrom $ ./build/cbfstool build/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 sgabios support
An sgabios option ROM can forward many VGA BIOS requests and keyboard events over a serial port. One can deploy it in addition to the primary VGA BIOS or by itself.
If the target machine does not have a VGA adapter, then one should install sgabios. Most bootloaders (eg, GRUB) require a VGA BIOS in order to function properly — the sgabios ROM can fill this requirement.
Place the sgabios ROM file in the vgaroms/ directory of CBFS. For example:
<source lang="bash"> $ ./build/cbfstool build/coreboot.rom add -f /path/to/sgabios.bin -n vgaroms/sgabios.bin -t raw $ ./build/cbfstool build/coreboot.rom print </source>
When using sgabios, all the characters that SeaBIOS writes to the screen will be seen twice — once from SeaBIOS sending the character to the serial port and once from sgabios forwarding the character. To prevent the duplicates set the config file etc/screen-and-debug to zero.
Using coreboot VGA support
Coreboot can initialize the GPU of some mainboards. After initializing the GPU, the information about it is passed to the payload.
SeaBIOS can provide an option rom that implements legacy VGA BIOS compatibility for coreboot initialized GPUs. To use this feature select CONFIG_VGA_COREBOOT (in "make menuconfig" under "VGA ROM ---> VGA Hardware Type" select "coreboot linear framebuffer").
The resulting option rom out/vgabios.rom should be added to the vgaroms/ directory of CBFS. For example:
<source lang="bash"> $ ./build/cbfstool build/coreboot.rom add -f /path/to/seabios/out/vgabios.bin -n vgaroms/seavgabios.bin -t raw $ ./build/cbfstool build/coreboot.rom print </source>
One should note that many bootloaders expect some vbios functionality which this vgabios does not provide. To overcome this issue one can use a bootloader not requiring this functionality. For instance grub works fine if configured in textmode. To achieve this comment out or add to /etc/default/grub:
and regenerate the grub configuration:
<source lang="bash"> grub-mkconfig -o /boot/grub/grub.cfg </source>
Geode option roms
There are two VGA option roms for geode in SeaBIOS, they can be found in "VGA ROM --->" in "make menuconfig":
- The first one is for the Geode LX, its named "GeodeLX" in "make menuconfig"
- The second one if for the Geode GX2, its named "Geode GX2" in "make menuconfig"
Adding a graphical "bootsplash" image
SeaBIOS can show a custom JPEG image or BMP image during bootup. To enable this, add the JPEG file to flash with the name bootsplash.jpg or BMP file as bootsplash.bmp. For example:
<source lang="bash"> $ ./build/cbfstool build/coreboot.rom add -f /path/to/image.jpg -n bootsplash.jpg -t raw $ ./build/cbfstool build/coreboot.rom print </source>
The size of the image determines the video mode to use for showing the image. Make sure the dimensions of the image exactly correspond to an available video mode (eg, 640x480, or 1024x768), otherwise it will not be displayed.
SeaBIOS will show the image during the wait for the boot menu (if the boot menu has been disabled, users will not see the image). The image should probably have "Press F12 for boot menu" embedded in it so users know they can enter the normal SeaBIOS boot menu. By default, the boot menu prompt (and thus graphical image) is shown for 2.5 seconds. This can be customized via a configuration parameter.
The JPEG viewer in SeaBIOS uses a simplified decoding algorithm. It supports most common JPEGs, but does not support all possible formats. Please see the Trouble reporting section if a valid image isn't displayed properly.
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"> $ ./build/cbfstool build/coreboot.rom add -f /path/to/gpxe/src/bin/10ec8167.rom -n pci10ec,8167.rom -t optionrom $ ./build/cbfstool build/coreboot.rom print </source>
As with VGA option ROMs, the gpxe option ROM may be compressed with LZMA. However, compression won't significantly reduce gpxe's size as it implements its own compression.
In addition to gpxe, other option ROMs can be added in the same manner.
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"> $ ./build/cbfstool build/coreboot.rom add-payload -f /path/to/payload.elf -n img/MyPayload $ ./build/cbfstool build/coreboot.rom print </source>
During boot, one can press the ESC key to get a boot menu. SeaBIOS will show all files in the img/ directory, and one can instruct SeaBIOS to run them.
SeaBIOS supports both uncompressed and LZMA compressed payloads.
Adding a floppy image
It is possible to embed an image of a floppy in flash. SeaBIOS can then boot from and redirect floppy BIOS calls to the flash image. This is mainly useful for legacy software (such as DOS utilities). To use this feature, place a floppy image into the CBFS directory floppyimg/. For example:
<source lang="bash"> $ ./build/cbfstool build/coreboot.rom add -f /path/to/myfloppy.img -c lzma -n floppyimg/MyFloppy.lzma -t raw $ ./build/cbfstool build/coreboot.rom print </source>
Both uncompressed and LZMA compressed images are supported. Several floppy formats are available: 360K, 1.2MB, 720K, 1.44MB, 2.88MB, 160K, 180K, 320K. SeaBIOS expects the uncompressed images size to be equal to the ones just mentioned. Else, given enough debug, it will complain with: "No floppy type found for ramdisk size".
The floppy image will appear as writable to the system, however all writes are discarded on reboot.
When using this system, SeaBIOS reserves high-memory to store the floppy. The reserved memory is then no longer available for OS use, so this feature should only be used when needed.
Configuring boot order
Place a file in CBFS with the name bootorder to configure the boot up order. The file should be ASCII text and contain one line per boot method. The description of each boot method follows an Open Firmware device path format. SeaBIOS will attempt to boot from each item in the file — first line of the file first.
The easiest way to find the available boot methods is to look for "Searching bootorder for" in the SeaBIOS serial output. For example, one may see lines similar to:
Searching bootorder for: /pci@i0cf8/*@f/drive@1/disk@0 Searching bootorder for: /pci@i0cf8/*@f,1/drive@2/disk@1 Searching bootorder for: /pci@i0cf8/usb@10,4/*@2
The above represents the patterns SeaBIOS will search for in the bootorder file. However, it's safe to just copy and paste the pattern into bootorder. For example, the file:
will instruct SeaBIOS to attempt to boot from the given USB drive first and then attempt the given ATA harddrive second.
Once a file has been created, add it to CBFS with the name bootorder. For example:
<source lang="bash"> $ ./build/cbfstool build/coreboot.rom add -f mybootlist.txt -n bootorder -t raw $ ./build/cbfstool build/coreboot.rom print </source>
Other Configuration items
Additional configuration options are available in the CBFS etc/ directory. For example, to set the duration of the boot menu to five and a half seconds, one would do the following:
<source lang="bash"> $ ./build/cbfstool build/coreboot.rom add-int -i 5500 -n etc/boot-menu-wait $ ./build/cbfstool build/coreboot.rom print </source>
The cbfstool "add-int" command will create a litte-endian encoded binary integer and place it into the specified CBFS file.
See the SeaBIOS wiki for details on available options.
It is possible to create the equivalent of "symbolic links" in CBFS so that one file's content appears under another name. To do this, create a links file with one line per link and each line having the format of "linkname" and "destname" separated by a space character. For example, the "links" file may look like:
pci1234,1000.rom somerom.rom pci1234,1001.rom somerom.rom pci1234,1002.rom somerom.rom
Then add the "links" file to CBFS:
<source lang="bash"> $ ./build/cbfstool build/coreboot.rom add -f links -n links -t raw $ ./build/cbfstool build/coreboot.rom print </source>
The above example would cause SeaBIOS to treat "pci1234,1000.rom" or "pci1234,1001.rom" as files with the same content as the file "somerom.rom".
If you are experiencing problems with SeaBIOS, please follow the directions on the SeaBIOS wiki to report the issue.