Arduino MiniOS is a tiny multi-tasking operating system for Arduino. It was developed during a course focusing on assembler programming and operating system internals.
This operating system currently serves demonstrational purpose and is not thought to be a mature OS for productional use. Although it can and probably will be enhanced and further developed.
You may also have a look at AVRShell which is a far more mature version of this.
The core components of MiniOS is a dispatcher (context_switch()) and a
dumb scheduler (get_next_proc()). Both are implemented in the file process.S. The time slices for context switching are defined by the T0
timer interrupt, every ~16ms on a 16 MHz Arduino board. The code is found in timer.S. This file additionally contains an uptime counter which is used
in the function wait() in ledproc.c which sleeps a specific number
of time slices. Process.S also contains the function to start new
processes (start_proc()). After system initialization a single task
(main()) is started by the OS (see below). All other processes have to be
started subsequently by main() or its sub-processes by calling start_proc().
The file serial_io.S contains the code for complete interrupt driven
sending and receiving of data on the serial line. In this case it is used for a
tiny command line interface (which actually does not know any commands at the
current stage of development ;) ).
The system is initialized in init.S. This is initializing the interrupts,
the timer and all registers and starts the first initial task which is main() located in the file main.S. Main() can then start further child processes.
Currently two processes are running: main() which implements the command
line and serial communication and led_proc() which toggles the LED on
the Arduino board. The latter is implemented in C to show the interference
between C and Assembler on AVR by following the calling conventions accordingly.
Arduino MiniOS is developed and maintained by Bernhard R. Fischer, 4096R/8E24F29D bf@abenteuerland.at. You may also follow me on Twitter or read my tech and society blog. You may also have a look at my collection of Arduino materials.
Feel free to contact me :)
This code is completely free. Do what every you like with it and buy me a beer.