PLAYING WITH OLD CISCO® IP PHONES

Cisco® IP phones are generally found everywhere in offices for the last nearly 20 years. As of this writing, there are several models that have reached their end of life and official support from Cisco®. One such model is the CP-7961G-GE which I was able to get on eBay for $15.99 with free shipping, so I purchased two of them. I also ended up purchasing the CP-7975G for $18 with free shipping. When purchased new these phones cost more than $200 to buy one.

This is going to be a series of posts in my adventures with these phones, with this being the introductory one. Several people have setup these end-of-life phones with Asterisk or FreePBX and I will be doing the same. In addition to that, I will try to get to the internals of the phone and understand the chipset and write applications that run on the phone.

NEW LIFE WITH JEKYLL!

After more than 10 years of using a custom Perl script to generate this static website and not making any updates to it, I have finally gone the distance and converted the site to work with Jekyll which is written in Ruby, a language that I can read but cannot write. This brings my site into the modern world of using Markdown to write my pages and posts, and be able to add information much more quickly than I would do with my custom Perl script. The CSS theme is still the same ncurses-style old-school retro look of a DOS terminal from the 1990s, that I had developed around 2010 from scratch and continue to use. Although, I did switch to using Monospace font as a default for readability.

x86-64 TUTORIAL: HILBERT MATRIX

The aim of solving this problem is to learn how to use the XMM registers for multiplication of floating point numbers. Matrix multiplication is a slow calculation especially if the floating point unit is used, and hence doing packed floating point calculations (if double precision is not required) might just be much faster. So this program will test that.

LABOUCHERE SYSTEM PROGRAM USING x86-64 REGISTERS

This program does not use any fixed memory locations for the head or tail of the link list, but uses all the registers available to it. However, for some of the functions it does not follow the convention of saving all the registers RBX, R12-R15 on the stack at every function call since some of these registers contain pointers to the head and tail of the link list. Even if we did that, the program would hardly change much.

LABOUCHERE SYSTEM C PROGRAM

Here is the full C code for the Doubly Linked List: Labouchere System.