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" );
}
/*--------------------------------------------------*/
下一节： RTOS 实现 - AVR 上下文
Copyright (C) Amazon Web Services, Inc. or its affiliates. All rights reserved.
|
