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The Implementation of the ULIX Literate Operating System

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A diary documenting the implementation of ULIX-i386

Welcome to the ULIX blog.

Ulix (Literate Unix) is a Unix-like operating system developed at University of Erlangen-Nürnberg. I use D. E. Knuth's concept of Literate Programming for the implementation and documentation. The goal was a fully working system which can be used in operating system courses to show students how OS concepts (such as paging and scheduling) can be implemented. Literate programs are very accessible because they can be read like a book; the order of presentation is not enforced by program logic or compiler restrictions, but instead is guided by the implementer's creative process.

Ulix is written in C and assembler for the Intel architecture. The literate programming part is handled by noweb.

On this page I document my progress with the implementation.


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User Mode (21.08.2011)


Ulix can now switch to user mode and execute simple code. Since we have no syscalls yet, it cannot do much in user mode. So the next step is to set up syscalls for "print character" and "read character" -- then I can convert the current simple shell into a user mode shell. This is not yet a process, it is just code being executed with privilege level 3 (in ring 3) instead of the kernel's own privilege level 0 (ring 0). However, it's nice to have it, because the transition from kernel to user mode requires weird code and a TSS (Task State Segment).

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