Operating Systems - TinyOS-3

Kernel extensions for TinyOS-3, a small educational operating system written in C11, developed for the Operating Systems Lab at the Technical University of Crete (2021–22).

TinyOS-3 does not run on real hardware. It runs as a Linux process on top of a simulated multi-core machine (CPU cores, timers, terminals), while still doing the core jobs of an OS kernel: creating, scheduling and terminating processes and threads, and handling I/O.

The base code comes from vsamtuc/tinyos3.

What was implemented

Part 1 - Threads and Scheduling

Multithreaded processes. System calls CreateThread, ThreadSelf, ThreadJoin, ThreadExit and ThreadDetach, built on a new Process Thread Control Block (PTCB) that links each thread to its TCB and PCB.

Multilevel Feedback Queue scheduler. Replaces the original Round-Robin scheduler with 20 priority queues. A thread's priority drops when it uses up its time quantum and rises when it blocks on I/O. All threads are periodically boosted to prevent starvation.

Part 2 - Inter-Process Communication and System Info

Pipes. One-way byte streams with a circular buffer. Readers and writers block when the buffer is empty or full.

Sockets. Local stream sockets with Socket, Listen, Accept, Connect and ShutDown, built on top of pipes and using a port map.

System information. OpenInfo lets user programs (e.g. ps in the shell) read information about running processes, like /proc in Linux.

Build & Run

Requires Linux with gcc and make.

cd tinyos3
touch .depend
make
./mtask 1 0 1 1          # run the demo program
./tinyos_shell 1 1       # start the TinyOS shell (1 core, 1 terminal)

Testing

The implementation passes the full validate_api test suite:

./validate_api

Suite	Tests	Result
basic_tests	31	✅ passed
thread_tests	14	✅ passed
pipe_tests	6	✅ passed
socket_tests	25	✅ passed