yaos

yaos is an embedded operating system for Internet of Things(IoT) devices, specifically for a single-core processor without MMU virtualization. It is designed for energy efficiency and hardware independent development.

Refer to /Documentation directory for more information such as compiling, porting, APIs, etc.

Any feedback is welcome to kwon@toanyone.net. And let me know if any of you are interested in porting to new MCU so that I can give you a hand.

Getting Started

1. Download yaos

git clone git://github.com/onkwon/yaos

2. Get a Toolchain

Get one from here if you don't have one installed yet. Or you can compile it from source code putting more effort, which is not recommended but still worth trying.

3. Build

STM32

make clean
make stm32f1 (or specify your board. e.g. mango-z1)
make
make burn

Supported boards at the moment are :

mango-z1

mycortex-stm32f4

nrf52

stm32f429i-disco

stm32f469i-disco

stm32-lcd

ust-mpb-stm32f103

stm32f1-min

In case of getting error messages something like undefined reference to __aeabi_uidiv, specify library path when you make in the way below:

make LD_LIBRARY_PATH=/usr/local/arm/lib/gcc/arm-none-eabi/4.9.2

The path is dependent on your development environment.

User task example

Let me put an example of blinking a LED for you to take a taste of how the code look like.

User tasks would be placed under /tasks(e.g. tasks/my-first-task.c):

void main()
{
	int fd, led = 0;

	if ((fd = open("/dev/gpio20", O_WRONLY)) <= 0) {
		printf("can not open, %x\n", fd);
		return;
	}

	while (1) {
		write(fd, &led, 1);
		led ^= 1;
		sleep(1);
	}

	close(fd);
}
REGISTER_TASK(main, 0, DEFAULT_PRIORITY, STACK_SIZE_DEFAULT);

Features

Task management and scheduling

Two types of task are handled: normal and real time tasks. Round-robin scheduler for normal tasks while priority scheduler for real time tasks. Each task is given a priority which can be dynamically changed with set_task_pri(). For real time tasks a higher priority task always preempts lower priority tasks while the same priority tasks take place in turn under round-robin scheduling. Scheduler can be stopped to reduce even the scheduling overhead in case of a time critical task. On the other hand normal tasks get chance to run by simplified fair scheduler, that picks the minimum value of runtime up for the next task to run.

Tasks are always in one of five states: running, stopped, waiting, sleeping, or zombie. And a task can be created both statically and dynamically at run-time.

System call interface

System resource is accessed by the system call interface entering privileged mode as a user task runs in user(unprivileged) mode.

Virtual file system

The concept of virtual file system(VFS) is implemented. The embedded flash rom in SoC can be mounted as the root file system(embedfs) while a ramfs is mounted as a devfs for a device node.

Empty flash memory is registerd as embedfs so that user can use it just like normal file system.

Memory management

Page is unit of memory management but alternative memory manager can be used in such a system of memory shortage.

Buddy allocator and first-fit allocator are implemented.

Deferred interrupt servicing (softirq)

Softirqs will preempt any work except the response to a real interrupt as they run at a high priority. In fact softirq is just a kernel task running with interrupts enabled and can sleep but has the highest priority amongst running tasks.

onkwon/yaos