NOTE! NOTE! NOTE! NOTE! NOTE! NOTE! NOTE! NOTE! NOTE! NOTE! NOTE! NOTE!
/dev/bios is obsolete and no longer under development.
Please use the flashrom utility instead: https://www.flashrom.org/
NOTE! NOTE! NOTE! NOTE! NOTE! NOTE! NOTE! NOTE! NOTE! NOTE! NOTE! NOTE!
/dev/bios documentation 2002/02/19
Table of contents
------------------
1. What is /dev/bios?
2. What hardware/software do I need to run /dev/bios?
3. Where to get the latest release of /dev/bios
4. How to get /dev/bios work
5. Writing to the devices
6. About PCI chipsets (ix86 only)
7. About APM Powermanagement (ix86 only)
8. About different flashchips.
9. Hints for BIOS flashing
If you want better information on this driver, read the ChangeLog,
mail me or read the source, Luke :-)
1. What is /dev/bios?
----------------------
This is a kernel driver for different kinds of (Flash)BIOSs that are
available in today's hardware.
There are well known BIOSs for
- System BIOS (resides at 0xe0000 on Intel PCs)
- graphics hardware
- SCSI host adapters
- networking interfaces with 'BOOT ROM'
- ...
While in former times these BIOSs were implemented by using ROM or
EPROM (both can't be updated without opening your computer) today's
PC hardware is often delivered with so called FLASH ROMs. These
can simply be updated by software. This driver has the approach to
make Linux read and write flash roms.
One word before you read ahead: This is still alpha software and
writing to your flash roms may destroy them. So if you notice anything
strange, don't even think about going on, but write some mail to:
Stefan Reinauer <stefan.reinauer@coreboot.org>
Please note that I am not responsible in any way for what you
do with this code or for what this code does with your computer.
2. What hardware/software do I need to run /dev/bios?
------------------------------------------------------
Currently this driver supports ix86 (mainly Pentium,
PPro, PII/III, Athlon, but some 486s), Itanium and Alpha
architecture.
It supports all flash chips from 32k to 2M (theoretically).
Minimum kernel version is v2.2.x, but it's wise to use a
2.4.x kernel.
3. Where to get the latest release of /dev/bios?
-------------------------------------------------
/dev/bios was recently integrated into the OpenBIOS CVS
tree for easier maintainance. General information can be
found on the /dev/bios status page:
http://www.freiburg.linux.de/OpenBIOS/status/devbios.html
Latest releases of /dev/bios can be found at the download page:
http://www.freiburg.linux.de/OpenBIOS/dev/download.html
Latest development trees of /dev/bios can be found in the
OpenBIOS CVS. For information how to access it, go to
http://www.freiburg.linux.de/OpenBIOS/dev/cvs.html
4. How do I get /dev/bios work
-------------------------------
Create the system bios device with
mknod /dev/bios c 104 0
Now you can add devices for the other BIOSs (often known as option
roms) in your Computer, i.e. like this:
mknod /dev/gfxbios c 104 1
mknod /dev/hddbios c 104 2
mknod /dev/netbios c 104 3
The order of the devices may vary on your computer, maybe you even don't
have a flash bios on your network card or on your scsi host adapter. You will
have to decide this after playing around a bit.
Now you have to compile and insert the kernel driver module:
cd devbios
make clean && make
insmod bios.o
Now you have a new device, /dev/bios and, if you have
your kernel configured to have the /proc/ interface,
you have a status file /proc/bios.
Since this driver is in an early state, you should have
a look at dmesg very often.
5. Writing to the devices
--------------------------
If you insert bios.o without any options, you are not able
to write any of the devices. To enable writing, you should
use
insmod bios.o write=1
Writing is now possible with i.e.
dd if=yourbios.bin of=/dev/bios bs=128k count=1
or
dd if=yourbios.bin of=/dev/bios bs=256k count=1
depending on the size of your flash chip.
You can use 'cat' for flashing as well. Note: Many flashchips are
sectored and the whole sector has to be rewritten, the 4k clusters
of cat may be very slow (and an 112 kb sector has to be written 28
times completely instead of 1 time with dd)
Make sure that your file "yourbios.bin" is a valid bios image for
your motherboard and that it is not pkzipped or exe-pkzipped.
(Usually, a 128kb bios images consist of 112kb lha-compressed data,
2*4kb ESCD and DMI (PnP) Data and an 8 kb emergency boot block.)
Writing to /dev/bios does not work for many chips right now. Write
accesses are ignored in this case. If you want an unsupported flash
rom supported, please mail me.
WARNING: Setting an unsupported chip to "supported" without changing
the rest of the code will *very likely* destroy the contents of your
chip.
On machines with an AWARD bios you can test whether writing works
safely by only deleting the ESCD/DMI memory on the flash chip.
This data is rewritten by the bios when empty, corrupted or when
you put in a new expansion device. In that case you should see a
message stating "Updating ESCD" during the next boot.
Please have a close look at the size of your flash chip. For 128k
flash chips, try
dd if=/dev/zero of=/dev/bios bs=4096 seek=28 count=2
For 256k flash chips, you _MUST_ use the following line instead,
or your system bios is going byebye:
dd if=/dev/zero of=/dev/bios bs=4096 seek=56 count=2
Attention: I found other machines with their ESCD memory in the
first sectors of the flash chip. These are afaics 512k+ chips
often connected via a firmware hub.
Behaviour of other BIOSs may be similar, but I can't give you
any warranty it works.
NOTE: If you listen to music from your soundcard while flashing,
you may get errors like this:
Sound: DMA (output) timed out - IRQ/DRQ config error?
Second, sound switches off while flashing. This is because all
IRQs are blocked while the write procedure to ensure it doesn't
get disturbed by any other hardware.
6. About PCI chipsets
----------------------
Because this driver uses direct PCI accesses to switch shadowing
and write protection of the bios off on PC architecture, each PCI
chipset (or at least chipset group) has to be implemented and
tested seperately. Successfully tested PCI chipsets are
* Intel 430HX/TX, 440BX/ZX, 460, 8x0
* UMC 486 (8881F/8886A)
* VIA (M)VP3
* AMD Irongate and others
* ServerWorks chipsets
* NSC CS5530 (geode companion)
Any success/error reports are highly welcome. If you need a certain
system type supported, contact me.
7. About APM Power Management (ix86 only)
------------------------------------------
This driver is known to cause kernel oopses with some of the chipset
drivers when APM is enabled. Reason is that the flash chip is mapped
to the low bios address space which makes the unpacked bios image vanish
so all pointers to APM functions are invalid.
Nowadays most of the chipset drivers only map the high bios area, so
this problem should not occur on any but old UMC/SiS chipsets. If you
encounter oopses while reading/probing flash devices, disable power
management before any write attempts. To achieve so, please pass "apm=off"
as a kernel option, if your kernel is compiled with APM support.
8. About different flashchips
------------------------------
Flash chips, /dev/bios has been successfully tested (writing) on:
* Winbond 29EE011
* Intel 28F008(SA)
* Atmel AT29C512
* SST 29EE010, 39SF020
It *should* work, if you see a "Supported: yes" in /proc/bios, but
I am not responsible in any way for what you do.. Please be careful.
Please report any working flash chips so that this list can be completed.
Currently many more flash chips than mentioned here will work.
If you need a certain flash device supported, contact me.
9. Hints for BIOS-Flashing
---------------------------
* Always try to write to the ESCD/DMI Memory before you overwrite the rest
of a bios (ix86) If you get ANY errors in dmesg output, DO NOT CONTINUE!
* Always "diff" the new bios with the written image before rebooting
* You may use comp, a little utility in the devbios source tree instead
of diff. It has a nicer output for binary files.
* on Intel, only write the first 120k of an image to the System ROM, this keeps
the emergency bootblock working.
************** FINAL NOTE *****************************
If you want to help this project, send me
* /proc/bios-output
* dmesg-output (after insmodding the driver)
* your system-configuration
(e.g. output of lspci or /proc/bus/pci/devices)
* any comments
* any ideas
Stefan Reinauer <stefan.reinauer@coreboot.org>
