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README


Broadcom-SSB SPROM data modification tool
=========================================

About this software
-------------------

A tool for the convenient modification of the
Broadcom Sonics Silicon Backplane SPROM.
This tool automatically adjusts the CRC after the modification.

Requirements
------------

1) C99 compatible compiler.


Usage
-----

The contents of the sprom are exposed to the user in sysfs. This
tool can, in principle, read and write the sprom in place; however,
making a mistake during sprom writing could render your device
unusable. For this reason, we recommend copying the sprom contents
to disk as the first step. This copy can then be modified until it
contains the desired new information. Only then and with caution
should the sprom be rewritten. DO NOT MAKE ANY CHANGES UNLESS YOU
KNOW WHAT YOU ARE DOING!!!! You have been warned!!!

Obtaining a disk copy of the sprom contents
-------------------------------------------

This file name for the sprom contents depends on the bus layout of
the specific computer being used and will be something like

/sys/devices/pci0000:00/0000:00:0d.0/0000:04:00.0/ssb_sprom

It is not recommended that you try to type the name. Instead, you
should use the following commands to get and check the path for the
sprom file:

SSB_SPROM=$(find /sys -name ssb_sprom)
echo $SSB_SPROM

If the echo command only results in a single instance of "/sys/...",
you may proceed. For systems with more than one SSB-based interface,
there will be such a string for each, and the command that sets the
SSB_SPROM symbol will have to be changed. In the name above, the
sequence states that this device is attached to the 0'th PCI bus via
bridge 0d.0 and is device 04:00.0 on that bridge. To find which of
your SSB devices to select, use the 'lspci -v' command. On my system,
the first line of such output for my interface is "04:00.0 Network
controller: Broadcom Corporation BCM94311MCG wlan mini-PCI (rev 02)".
To select only this device, one would use

SSB_SPROM=$(find /sys -name ssb_sprom | grep 04:00.0)
echo $SSB_SPROM

Of course, the "04:00.0" needs to match your system, and check the
output value to determine that there is now a single instance of
"/sys..." and that the path matches the device whose SPROM is to be
changed. If not, adjust the string after 'grep' accordingly.

Once the SSB_SPROM variable matches the path to ssb_sprom for your
device, get a working copy of the sprom contents with

sudo cat $SSB_SPROM > ssb_sprom_copy

Modifying the contents of the working copy
------------------------------------------

You may now see the contents of your sprom with the command

ssb-sprom -i ssb_sprom_copy -P

As an example, let us suppose that you have purchased a Dell mini-pci
card to use in an HP laptop. The HP BIOS refuses to use the card when
the pcivendor is Dell (code 0x1028), not HP (code 0x103C). From the
information provided by an "ssb-prom --help" command, we learn that
the switch needed to change this vendor code is "--subv". To change
that code, we use the command

ssb-sprom -i ssb_sprom_copy -o new_ssb_sprom_copy --subv 0x103C

to write the HP vendor ID to our working copy. I use different
input and output files so as not to destroy the original. If further
changes are needed, for example the PCI product ID, the command

ssb-sprom -i new_ssb_sprom_copy -o new_ssb_sprom_copy --subp 0x137C

would be used. Note that the input and output files may be the same.
Once you think you have updated correctly, use

ssb-sprom -i new_ssb_sprom_copy -P

to check the contents.

Rewriting the sprom contents
----------------------------

Once the sprom contents are the way you want them, and presumably
correct, you are ready to rewrite the file. First, use

echo $SSB_SPROM

to ensure that this symbol still contains the SPROM path. If not,
then it will have to be reloaded as discussed above.

You are then ready to rewrite the sprom with

sudo cp new_ssb_sprom_copy $SSB_SPROM

Once again, you are urged to be absolutely certain of the contents
of the working copy BEFORE taking this step. If your interface
becomes unusable as a result of writing incorrect data into the
sprom, the responsibility is YOURS. Once again, you have been warned.