[SeaBIOS] [PATCH] docs: Add page on available CBFS/fw_cfg runtime config files
kevin at koconnor.net
Thu Feb 19 20:33:36 CET 2015
Signed-off-by: Kevin O'Connor <kevin at koconnor.net>
Much of the content on this page is also on the coreboot SeaBIOS wiki
page. After adding this page to the SeaBIOS wiki, my intent would be
to prune back the contents of the coreboot page and instead point to
the new SeaBIOS wiki page. (Though, I would leave most of the
examples in place on the coreboot page.)
I think it would be better for this to be in the SeaBIOS repo so that
new config settings and changes can be documented at the same time
they are updated.
docs/Developer_Documentation.md | 8 +-
docs/Runtime_config.md | 189 ++++++++++++++++++++++++++++++++++++++++
2 files changed, 193 insertions(+), 4 deletions(-)
create mode 100644 docs/Runtime_config.md
diff --git a/docs/Developer_Documentation.md b/docs/Developer_Documentation.md
index 843d612..24bf48a 100644
@@ -10,12 +10,12 @@ page.
See details on [building SeaBIOS](Build overview).
There is also information on the SeaBIOS [Memory Model](Memory Model).
Along with information on SeaBIOS [Execution and code flow](Execution
-and code flow).
+and code flow). A description of the process of linking the final
+SeaBIOS binary is available at [Linking overview](Linking overview).
-A description of the process of linking the final SeaBIOS binary is
-available at [Linking overview](Linking overview).
+The list of available runtime configuration items is at
To debug SeaBIOS and report problems see SeaBIOS
[debugging](Debugging). To contribute changes to SeaBIOS see
diff --git a/docs/Runtime_config.md b/docs/Runtime_config.md
new file mode 100644
@@ -0,0 +1,189 @@
+SeaBIOS can read several configuration items at runtime. On coreboot
+the configuration comes from files located in CBFS. When SeaBIOS runs
+natively on QEMU the files are passed from QEMU via the fw_cfg
+This page documents the user visible configuration and control
+features that SeaBIOS supports.
+On coreboot, when scanning files in CBFS, any filename that ends with
+a ".lzma" suffix will be treated as a raw file that is compressed with
+the lzma compression algorithm. This works for option ROMs,
+configuration files, floppy images, etc. . (This feature should not be
+used with embedded payloads - to compress payloads, use the standard
+section based compression algorithm that is built into the payload
+For example, the file **pci1106,3344.rom.lzma** would be treated the
+same as **pci1106,3344.rom**, but will be automatically uncompressed
+A file is typically compressed with the lzma compression command line
+tool. For example:
+`lzma -zc /path/to/somefile.bin > somefile.bin.lzma`
+However, some recent versions of lzma no longer supply an uncompressed
+file size in the lzma header. (They instead populate the field with
+zero.) Unfortunately, SeaBIOS requires the uncompressed file size, so
+it may be necessary to use a different version of the lzma tool.
+It is possible to create the equivalent of "symbolic links" 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:
+The above example would cause SeaBIOS to treat "pci1234,1000.rom" or
+"pci1234,1001.rom" as files with the same content as the file
+SeaBIOS will scan all of the PCI devices in the target machine for
+option ROMs on PCI devices. It recognizes option ROMs in files that
+have the form **pciVVVV,DDDD.rom**. The VVVV,DDDD should correspond to
+the PCI vendor and device id of a device in the machine. If a given
+file is found then SeaBIOS will deploy the file instead of attempting
+to extract an option ROM from the device. In addition to supplying
+option ROMs for on-board devices that do not store their own ROMs,
+this mechanism may be used to prevent a ROM on a specific device from
+SeaBIOS always deploys the VGA rom associated with the active VGA
+device before any other ROMs.
+In addition, SeaBIOS will also run any file in the directory
+**vgaroms/** as a VGA option ROM not specific to a device and files in
+**genroms/** as a generic option ROM not specific to a device. The
+ROMS in **vgaroms/** are run immediately after running the option ROM
+associated with the primary VGA device (if any were found), and the
+**genroms/** ROMs are run after all other PCI ROMs are run.
+SeaBIOS can show a custom [JPEG](http://en.wikipedia.org/wiki/JPEG)
+image or [BMP](http://en.wikipedia.org/wiki/BMP_file_format) image
+during bootup. To enable this, add the JPEG file to flash with the
+name **bootsplash.jpg** or BMP file as **bootsplash.bmp**.
+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
+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
+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](Debugging) if a valid image
+isn't displayed properly.
+On coreboot, SeaBIOS will treat all files found in the **img/**
+directory as a coreboot payload. Each payload file will be available
+for boot, and one can select from the available payloads in the
+bootmenu. SeaBIOS supports both uncompressed and lzma compressed
+It is possible to embed an image of a floppy into a file. SeaBIOS can
+then boot from and redirect floppy BIOS calls to the image. This is
+mainly useful for legacy software (such as DOS utilities). To use this
+feature, place a floppy image into the directory **floppyimg/**.
+Using LZMA file compression with the [.lzma file
+suffix](#LZMA_compression) is a useful way to reduce the file
+size. Several floppy formats are available: 360K, 1.2MB, 720K, 1.44MB,
+2.88MB, 160K, 180K, 320K.
+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
+The **bootorder** file may be used 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
+device path format. SeaBIOS will attempt to boot from each item in the
+file â 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 debug output. For example,
+one may see lines similar to:
+SearchingÂ bootorderÂ for:Â /pci at i0cf8/*@f/drive at 1/disk at 0
+SearchingÂ bootorderÂ for:Â /pci at i0cf8/*@f,1/drive at 2/disk at 1
+SearchingÂ bootorderÂ for:Â /pci at i0cf8/usb at 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:
+/pci at i0cf8/usb at 10,4/*@2
+/pci at i0cf8/*@f/drive at 1/disk at 0
+will instruct SeaBIOS to attempt to boot from the given USB drive
+first and then attempt the given ATA harddrive second.
+SeaBIOS also supports a special "HALT" directive. If a line that
+contains "HALT" is found in the bootorder file then SeaBIOS will (by
+default) only attempt to boot from devices explicitly listed above
+HALT in the file.
+Other Configuration items
+There are several additional configuration options available in the
+| Filename | Description
+| show-boot-menu | Controls the display of the boot menu. Set to 0 to disable the boot menu.
+| boot-menu-message | Customize the text boot menu message. Normally, when in text mode SeaBIOS will report the string "\\nPress F12 for boot menu.\\n\\n". This field allows the string to be changed. (This is a string field, and is added as a file containing the raw string.)
+| boot-menu-key | Controls which key activates the boot menu. The value stored is the DOS scan code (eg, 0x86 for F12, 0x01 for Esc). If this field is set, be sure to also customize the **boot-menu-message** field above.
+| boot-menu-wait | Amount of time (in milliseconds) to wait at the boot menu prompt before selecting the default boot.
+| boot-fail-wait | If no boot devices are found SeaBIOS will reboot after 60 seconds. Set this to the amount of time (in milliseconds) to customize the reboot delay or set to -1 to disable rebooting when no boot devices are found
+| extra-pci-roots | If the target machine has multiple independent root buses set this to a positive value. The SeaBIOS PCI probe will then search for the given number of extra root buses.
+| ps2-keyboard-spinup | Some laptops that emulate PS2 keyboards don't respond to keyboard commands immediately after powering on. One may specify the amount of time (in milliseconds) here to allow as additional time for the keyboard to become responsive. When this field is set, SeaBIOS will repeatedly attempt to detect the keyboard until the keyboard is found or the specified timeout is reached.
+| optionroms-checksum | Option ROMs are required to have correct checksums. However, some option ROMs in the wild don't correctly follow the specifications and have bad checksums. Set this to a zero value to allow SeaBIOS to execute them anyways.
+| s3-resume-vga-init | Set this to a non-zero value to instruct SeaBIOS to run the vga rom on an S3 resume.
+| screen-and-debug | Set this to a zero value to instruct SeaBIOS to not write characters it sends to the screen to the debug ports. This can be useful when using sgabios.
+| advertise-serial-debug-port | If using a serial debug port, one can set this file to a zero value to prevent SeaBIOS from listing that serial port as available for operating system use. This can be useful when running old DOS programs that are known to reset the baud rate of all advertised serial ports.
+| floppy0 | Set this to the type of the first floppy drive in the system (only type 4 for 3.5 inch drives is supported).
+| floppy1 | The type of the second floppy drive in the system. See the description of **floppy0** for more info.
+| threads | By default, SeaBIOS will parallelize hardware initialization during bootup to reduce boot time. Multiple hardware devices can be initialized in parallel between vga initialization and option rom initialization. One can set this file to a value of zero to force hardware initialization to run serially. Alternatively, one can set this file to 2 to enable early hardware initialization that runs in parallel with vga, option rom initialization, and the boot menu.
More information about the SeaBIOS