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Boot files and tasks are now initialised together. Theads can ask for particular space and thread ids, if they're unused. This enables us to get predefined ids for known tasks such as the VFS task. Fixes to README Other minor fixes.
102 lines
5.1 KiB
Plaintext
102 lines
5.1 KiB
Plaintext
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Codezero Microkernel 'Toy' release
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Copyright (C) 2007 Bahadir Balban
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What is Codezero?
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Codezero is a small microkernel based on the L4 microkernel principles and has
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its own interpretation of the L4 microkernel API. In addition, it has server
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tasks that implement memory management, a virtual filesystem layer, and these
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servers currently support a small but essential subset of the POSIX API.
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Codezero project is an effort to implement a modern, open source operating
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system based on the latest technology in microkernel and OS design. It targets
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realtime, high-end embedded systems and has an emphasis on the ARM architecture.
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It is quite common to see open source projects developed in a closed-doors
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fashion. Codezero project goes beyond just publishing source code as open source
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but also uses the latest open source development practices such as those used by
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the Linux Kernel.
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Why the name Codezero?
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The project focuses on simplicity, elegance, cleanliness, which are important
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assets in software engineering. The philosophy is to implement a structurally
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complete system with most modern OS features while retaining simplicity in the
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implementation as much as possible. This objective also fits well with embedded
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platforms, which usually have rigorous memory and performance requirements. Also
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the project is written from scratch, so the name emphasises that.
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Design & Features:
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Based on L4 microkernel principles, there are only a few system calls in
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Codezero. These system calls provide purely mechanism; threads and address
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spaces, and the methods of inter-process communication between them. Anything
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beyond these are policy and they are implemented in the userspace. Due to this
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rigorously simple design the same microkernel can be used to design completely
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different operating systems. In terms of other features, the microkernel is
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preemptive, and smp-ready. Currently only synchronous communication is
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implemented, but this will change in the near future.
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MM0 is the systm task that implements memory management. It contains memory and
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page allocators. It implements demand paging by managing page faults, physical
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pages and their file/task associations.
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FS0 is the system task implements a simple, modern virtual filesystem layer.
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Since it abstracts the low-level filesystem details, it is a relatively easy job
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to port a new filesystem to be used under FS0.
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License:
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The current 'Toy' release is distributed under GNU General Public License
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Version 3 and this version only. Any next version will be released in the same
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license, but there are intentions to keep the project in a dual-licensed manner.
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In any case, the project source code will always be released as open source with
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copyleft clauses.
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The third party source code under the directories loader/ tools/ libs/c libs/elf
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have their own copyright and licenses, separate from this project. All third
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party source code is open source in the OSI definition. Please check these
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directories for their respective licenses.
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Why yet another POSIX microkernel?
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There are many open source POSIX operating systems with advanced features such
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as *BSD and Linux. However these were originally not designed for embedded
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systems. Unix itself and all the tools built upon weren't meant for using on
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small devices. Accordingly, these operating systems contain a lot of historical
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code. Linux is well established, and targets a broad range of platforms and
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uses, but consequently embedded platforms don't always get enough emphasis. Also
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such well established, mature systems tend to oppose major design overhauls,
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which limits innovation to a certain extent. In addition, their code base is so
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big, that it gets more and more difficult to understand how the system works.
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Usually much of the code is irrelevant to the problem, in case of embedded
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systems. Codezero is written from scratch to solely target embedded systems and
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as such the source code is %100 relevant. It is small and free from legacy code.
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Finally monolithic kernels may have issues with dependability due to much of the
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code sharing the same address space. Being a microkernel design, Codezero aims
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to defeat this problem and increase dependability.
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Other than these modern kernels, there is systems software targeting embedded
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devices. Most of them are proprietary, with their own users. Some of the open
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source ones are structurally too simplistic, and lack modern features such as
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paging. There are existing well-designed embedded OS'es, but Codezero provides
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an alternative that will follow the open source development principles more
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closely. This will prove useful because many embedded systems still use older
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development methods and the right open source methodology would prove favorable
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in the fast-paced nature of development.
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Finally, there are new ideas in OS literature that would improve Unix but aren't
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implemented either because they have no existing users or may break compatibility
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somewhat (e.g. some are presented in Plan 9). As well as practising realistic
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development methodologies, Codezero project aims to keep up with the latest OS
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literature and provide the opportunity to incorporate the latest ideas in OS
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technology.
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