RT-Thread OS的启动流程

1、RT进入main之前，

SystemInit函数初始化时钟。

2、main函数位于startup.c文件中。进行两个工作

系统开始前，rt_hw_interrupt_disable关闭所有中断。

之后使用rtthread_startup启动RTThread

3、函数rtthread_startup()完成的工作：

1、调用函数rt_hw_board_init 完成板子初始化工作

2、显示版本信息：rt_show_version

3、初始化系统滴答：rt_system_tick_init

4、系统内核对象初始化：rt_system_object_init

5、定时器初始化：rt_system_timer_init

6、系统堆栈初始化rt_system_heap_init

7、任务调度器初始化：rt_system_scheduler_init

8、rt_application_init //加入用户自定义的任务

9、FINSH模块初始化 ,

10、定时器线程初始化：rt_system_timer_thread_init

11、空闲任务初始化rt_thread_idle_init

12、开始任务调度，OS接管MCU：rt_system_scheduler_start

任务调度开始之后，OS就算是启动好了。之后的东西都是在OS的管理下运行了。

4、在RTT示例工程中添加外设驱动的方法：

　　驱动头文件加入board.h

RT-thread系统的main函数位于startup.c文件中。

/**
 * This function will startup RT-Thread RTOS.
 */
void rtthread_startup(void)
{
    /* init board */
    rt_hw_board_init();//NVIC_config, SysTick_config, serial_device register, set CONSOLE for output(rt_kprintf(...)) in board.c

    /* show version */
    rt_show_version(); //show the version of rtthread by serial device(set to be console-device in board.c) in kservice.c 

    /* init tick */
    rt_system_tick_init();  //empty fucntion(since 1.1.0) in clock.c

    /* init kernel object */
    rt_system_object_init();//empty fucntion(since 0.3.0) in object.c

    /* init timer system */
    rt_system_timer_init(); //init rt_timer_list[0].next=rt_timer_list[0].prev=rt_timer_list[0](means rt_timer_list is empty) in timer.c

    rt_system_heap_init((void*)STM32_SRAM_BEGIN, (void*)STM32_SRAM_END);//init system heap in mem.c

    /* init scheduler system */
    rt_system_scheduler_init();//init the system scheduler, and init rt_thread_defunct(dead thread list) to be empty in scheduler.c

    /* init application */
    rt_application_init();     //init all defined thread in application.c

//#ifdef RT_USING_FINSH       //replace finsh_set_device() after the function of rt_components_init() in rt_init_thread_entry() of application.c
    /* init finsh */
    //finsh_system_init();    //INIT_COMPONENT_EXPORT(finsh_system_init) in shell.c, so it needn't finsh_system_init here
    //finsh_set_device( FINSH_DEVICE_NAME );//sets the input device of finsh shell(rt_device_open(dev, RT_DEVICE_OFLAG_RDWR | 
                                            RT_DEVICE_FLAG_INT_RX | RT_DEVICE_FLAG_STREAM) in shell.c
//#endif

    /* init timer thread */
    rt_system_timer_thread_init();//init system software timer thread(opened by #define RT_USING_TIMER_SOFT in rtconfig.h) in timer.c

    /* init idle thread */
    rt_thread_idle_init();        //init idle thread(cleanup all dead thread), then start to be ready in idle.c

    /* start scheduler */
    rt_system_scheduler_start();  //startup scheduler(first swith to the highest priority thread and enable interrupt )in scheduler.c

    /* never reach here */
    return ;
}

int main(void)
{
    /* disable interrupt first */
    //enable interrupt(CPSIE I) when the first thread switch(rt_hw_context_switch_to) in lipcpu/cortex-m4/context_rvds.S
    rt_hw_interrupt_disable();

    /* startup RT-Thread RTOS */
    rtthread_startup();

    return 0;
}