# Getting Started with Real-time Operating Systems

Video link: https://atollic.wistia.com/medias/gwgee6ev93

## RTOS Introduction
microcontroller
* before , 4~16K RAM, 8MHz CPU
* now, 16~32K RAM

we can build really cool stuff.

## Bare-metal scheduling technique

### Round-Robin Scheduling

int main(void) {
    System_Init();
    while (1) {
        Task1();
        
        Task2();
        
        Task3();
    }
    
    return 1;
}

* pros
* easy to implement
* cons
* Adding new task will change the real-time attribute (need to tune again)
* not the best for RTOS

#### Round-Robin scheduling improvement

With interrupts, we can change the current task.

### Cooperative Scheduling

* Read system time
* Run task1? yes: Task1, no: check next task
* Run task2? yes: Task2, no: read system time

* procs
* only need to check all task end with the deadline
* can have interrupt
* can have hard real-time
* cons
* Can't preemptive

## Task Concurrency

* Sequential Tasks
* Task 1
* Task 2
* Task 3
* Task 1
* ...
* Concurrent Tasks
* Task 1
* Task 3
* Task 1
* Task 2
* Task 1
* ...

## RTOS Characteristics

A **Real-Time Operating System (RTOS)** is an operating system designed to manage hardware resources of an embedded system with very precise timing and a high degree of reliability.

* Example 6 characteristics
* Reliability
* Predictability
* Performance
* Compactness
* Scalability
* Multi-Tasking

## Bara-metal or RTOS

* 7 Reason to choose an RTOS
* Concurrency
* Preemption
* a task to be interrupt by higher priority to run on the CPU
* In bare-metal, using preemption will make code too complex.
* Available RAM
* Available flash
* Sync tools
* 3rd party software
* Ease of use

## FreeRTOS


## Task Fundamentals


### Create Task

xTaskCreate(
    Led_BlueBlink,                       /* Task Pointer */
    (const char *const) "led_blue",      /* Task Name */
    configMINIMAL_STACK_SIZE,            /* Stack Depth */
    0,                                   /* Parameters to Pass to task */
    1,                                   /* Task Priority */
    0                                    /* Pass handle to create task */
);

### Task States


## FreeRTOS Resource