Description
This is an utility for packing/unpacking of Cisco IP Phone firmwares based on CNU_File_Archive_3.0 format, called so after strings found in firmware files. These are 7911/7906, 7941/7961, 7970/7971 and others for 79xx series phones.
Firmwares for 3911, 7931 and other newer models have different format and can't be unpacked with this utility.
About
Some development history and firmware format description is available, partly translated from Russian.
Download
Disclaimer number one
This version was never tested on real hardware. It is a rewrite of the very first working unpacker version. During my tests it repacks original firmware unpacked files with no binary difference, so I think it's safe to try.
Disclaimer number two
Original firmware files are distributed with digital signature placed at beginning of file. To unpack firmware file you should remove signature with tool included in distribution, see README. Actually, repacked files should be signed too, but phones accept unsigned firmwares by default. In case you use Cisco Call Manager with firmware security features enabled, you should disable this on per phone basis or find the way to sign modified firmwares with correct keys, possibly found in Call Manager. I don't really know.
Download cnu_fpu-0.2.tar.gz
How to use it
See README in archive.
What to do if you bricked your phone?
Take another $200 and buy new phone. Or better take your $200 and pay it to electronics guru who will fix phone bootloader with JTAG, and you then publish his research on the web. What you are not supposed to do is asking me why this tool turned your shiny phone into the brick.
7941 and higher models are viable ones, I have strange feeling they automatically revert to previous successful firmware after 10 tries to upgrade from TFTP. Possible this is not true, because I saw too much reboots of this devices while debugging my firmware, so I can be wrong interpreting its behavior.