FreeRTOS 滴答代码
[RTOS 实现构建块]

FreeRTOS AVR 移植使用的实际源代码与前文的示例略有不同。 vPortYieldFromTick() 本身是作为一个“裸”函数实现的，且上下文在 vPortYieldFromTick() 中存储和恢复。之所以这么做是为了实现非抢占式上下文切换（在这种情况下，任务阻塞了自己） ——这里不做描述。

因此，RTOS 滴答的 FreeRTOS 实现如下所示（请参阅源代码段注释以了解更多详情）：


void SIG_OUTPUT_COMPARE1A( void ) __attribute__ ( ( signal, naked ) );
void vPortYieldFromTick( void ) __attribute__ ( ( naked ) );

/*--------------------------------------------------*/

/* Interrupt service routine for the RTOS tick. */
void SIG_OUTPUT_COMPARE1A( void )
{
    /* Call the tick function. */
    vPortYieldFromTick();

    /* Return from the interrupt.  If a context
    switch has occurred this will return to a 
    different task. */
    asm volatile ( "reti" );
}
/*--------------------------------------------------*/

void vPortYieldFromTick( void )
{
    /* This is a naked function so the context
    is saved. */
    portSAVE_CONTEXT();

    /* Increment the tick count and check to see
    if the new tick value has caused a delay
    period to expire.  This function call can
    cause a task to become ready to run. */
    vTaskIncrementTick();

    /* See if a context switch is required.  
    Switch to the context of a task made ready
    to run by vTaskIncrementTick() if it has a
    priority higher than the interrupted task. */
    vTaskSwitchContext();

    /* Restore the context.  If a context switch
    has occurred this will restore the context of
    the task being resumed. */
    portRESTORE_CONTEXT();

    /* Return from this naked function. */
    asm volatile ( "ret" );
}
/*--------------------------------------------------*/

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FreeRTOS 滴答代码 [RTOS 实现构建块]

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FreeRTOS 滴答代码
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