codezero/README

		Codezero Microkernel 'Toy' release

		Copyright (C) 2007 Bahadir Balban


What is Codezero?

Codezero is a small microkernel based on the L4 microkernel principles and has
its own interpretation of the L4 microkernel API. In addition, it has server
tasks that implement memory management, a virtual filesystem layer, and these
servers currently support a small but essential subset of the POSIX API.

Codezero project is an effort to implement a modern, open source operating
system based on the latest technology in microkernel design. It targets
realtime, high-end embedded systems and has an emphasis on the ARM architecture.

It is quite common to see open source projects developed in a closed-doors
fashion. Codezero project goes beyond just publishing source code as open source
but also uses the latest open source development practices such as those used by
the Linux Kernel.


Why the name Codezero?

The project focuses on simplicity, elegance, cleanliness, which are assets
usually hard to achieve in software engineering. The philosophy is to implement
a structurally complete system with most modern and complex operating system
features while retaining simplicity in the implementation as much as possible.
Avoidance of code bloat is a short way to put it. This objective also fits well
with embedded platforms, which usually have rigorous memory and performance
requirements.


License:

The current 'Toy' release is distributed under GNU General Public License
Version 3 and this version only. Any next version will be released in the same
license, but there are intentions to keep the project in a dual-licensed manner.
In any case, the project source code will always be released as open source with
copyleft clauses.

The third party source code under the directories loader/ tools/ libs/c libs/elf
have their own copyright and licenses, separate from this project. All third
party source code is open source in the OSI definition. Please check these
directories for their respective licenses.


Why yet another Posix (micro) kernel?

There are many open source Posix operating systems with advanced features such
as *BSD and Linux. However these were originally not designed for embedded
systems. Unix itself and all the tools built upon weren't meant for using on
small devices. Besides, these operating systems naturally contain a lot of
historical code. Linux is well established, and targets a broad range of
platforms and uses, but consequently embedded platforms don't always get enough
emphasis. Also such well established, mature systems tend to oppose major design
overhauls, which limits innovation to a certain extent. In addition, their code
base is so big, that it gets more and more difficult to understand how the
system works. Usually %95 of the code is irrelevant to the problem, in case of
embedded systems. Codezero is written from scratch to solely target embedded
systems and as such the source code is %100 relevant. It is small and free from
legacy code. Finally monolithic kernels may have issues with dependability due
to much of the code sharing the same address space. Being a microkernel design,
Codezero aims to defeat this problem and increase dependability.

Other than these modern kernels, there is systems software targeting embedded
devices. Most of them are proprietary, with their own users. Some of the open
source ones are structurally too simplistic, and lack modern features such as
paging. There are certainly existing well-designed embedded operating systems,
but Codezero provides an alternative that will follow the open source
development principles more closely. Finally, there are new ideas in OS
literature that would improve Unix but aren't implemented either because they
have no existing users or may break compatibility somewhat. (E.g. some are
presented in Plan 9, or ReiserFS 4). As well as practising realistic development
methodologies, Codezero project aims to keep up with the latest OS literature
and provide the opportunity to incorporate the latest ideas in OS technology.