Home

LILOS

LILOS is a bare-bones OS for the Atmel AVR processor (currently the ATmega328p). It's designed to be simple, and to use no dynamic memory. It provides:

• Lightweight cooperative multitasking -- 37 bytes of RAM for a minimal task.
• Inter-task communication and synchronization based on message passing.
• Convenience libraries for using GPIO pins and the USART.

A Small Example

A tiny LILOS program that simply toggles pin B5 looks like this:

#include <lilos/gpio.hh>
#include <lilos/task.hh>

TASK(blinky, 32) {
  lilos::Pin led = PIN(B, 5);
  while (1) {
    led.toggle();
  }
}

NORETURN main() {
  lilos::schedule(blinky);
  lilos::startTasking();
}

Of course, a single task program isn't a great use for LILOS. A better example might echo characters on the USART while it toggles an LED:

#include <lilos/gpio.hh>
#include <lilos/task.hh>
#include <lilos/usart.hh>

TASK(blinky, 32) {
  lilos::Pin led = PIN(B, 5);
  while (1) {
    led.toggle();
    lilos::yield();
  }
}

TASK(echo, 32) {
  lilos::usart_init<38400>();
  while (1) {
    lilos::usart_send(lilos::usart_recv());
  }
}

NORETURN main() {
  lilos::schedule(blinky);
  lilos::schedule(echo);
  lilos::startTasking();
}

Many LILOS functions, like lilos::usart_recv above, cause the calling task to block. When a task blocks, other tasks get CPU time. Our blink task never uses any blocking calls, so we have to include an explicit lilos::yield call to give echo time.

More Information

• Tasks