1.启动分析

基于：rt-thread-v5.0.1
先执行：汇编代码startup_stm32f429xx.s开始运行，主要调用SystemInit和 __main

; Reset handler
Reset_Handler    PROC
                 EXPORT  Reset_Handler             [WEAK]
        IMPORT  SystemInit
        IMPORT  __main

                 LDR     R0, =SystemInit
                 BLX     R0
                 LDR     R0, =__main
                 BX      R0
                 ENDP

2.源码分析

路径：rt-thread-v5.0.1\src\components.c

#ifdef __ARMCC_VERSION
extern int $Super$$main(void);
/* re-define main function */
int $Sub$$main(void)
{
    rtthread_startup();
    return 0;
}
#elif defined(__ICCARM__)
/* __low_level_init will auto called by IAR cstartup */
extern void __iar_data_init3(void);
int __low_level_init(void)
{
    // call IAR table copy function.
    __iar_data_init3();
    rtthread_startup();
    return 0;
}
#elif defined(__GNUC__)
/* Add -eentry to arm-none-eabi-gcc argument */
int entry(void)
{
    rtthread_startup();
    return 0;
}
#endif

int rtthread_startup(void)
{
    rt_hw_interrupt_disable();

    /* board level initialization
     * NOTE: please initialize heap inside board initialization.
     */
    rt_hw_board_init();

    /* show RT-Thread version */
    rt_show_version();

    /* timer system initialization */
    rt_system_timer_init();

    /* scheduler system initialization */
    rt_system_scheduler_init();

#ifdef RT_USING_SIGNALS
    /* signal system initialization */
    rt_system_signal_init();
#endif /* RT_USING_SIGNALS */

    /* create init_thread */
    rt_application_init();

    /* timer thread initialization */
    rt_system_timer_thread_init();

    /* idle thread initialization */
    rt_thread_idle_init();

#ifdef RT_USING_SMP
    rt_hw_spin_lock(&_cpus_lock);
#endif /* RT_USING_SMP */

    /* start scheduler */
    rt_system_scheduler_start();

    /* never reach here */
    return 0;
}

路径：rt-thread-v5.0.1\src\components.c

void rt_application_init(void)
{
    rt_thread_t tid;

#ifdef RT_USING_HEAP
    tid = rt_thread_create("main", main_thread_entry, RT_NULL,
                           RT_MAIN_THREAD_STACK_SIZE, RT_MAIN_THREAD_PRIORITY, 20);
    RT_ASSERT(tid != RT_NULL);
#else
    rt_err_t result;

    tid = &main_thread;
    result = rt_thread_init(tid, "main", main_thread_entry, RT_NULL,
                            main_thread_stack, sizeof(main_thread_stack), RT_MAIN_THREAD_PRIORITY, 20);
    RT_ASSERT(result == RT_EOK);

    /* if not define RT_USING_HEAP, using to eliminate the warning */
    (void)result;
#endif /* RT_USING_HEAP */

    rt_thread_startup(tid);
}

路径：rt-thread-v5.0.1\src\components.c

void main_thread_entry(void *parameter)
{
    extern int main(void);

#ifdef RT_USING_COMPONENTS_INIT
    /* RT-Thread components initialization */
    rt_components_init();
#endif /* RT_USING_COMPONENTS_INIT */

#ifdef RT_USING_SMP
    rt_hw_secondary_cpu_up();
#endif /* RT_USING_SMP */
    /* invoke system main function */
#ifdef __ARMCC_VERSION
    {
        extern int $Super$$main(void);
        $Super$$main(); /* for ARMCC. */
    }
#elif defined(__ICCARM__) || defined(__GNUC__) || defined(__TASKING__) || defined(__TI_COMPILER_VERSION__)
    main();
#endif
}

#include <stdio.h>
#include <rtthread.h>

int main(void)
{
    return 0;
}