开发中发现FreeRTOS软件定时器不走了，具体表现在软件定时器中断进不去。
观察发现只有在某个任务执行期间，FreeRTOS的软件定时器才会不走，其他任务执行时正常，排查后是此任务的优先级比定时器任务高，且占用时间比较长，导致任务切不出去。
在FreeRTOSConfig.h中修改定时器任务优先级为最高解决问题
在看apollo3 代码时发现下面这个函数
void WsfSetOsSpecificEvent(void)
{
if(xRadioTaskEventObject != NULL)
{
BaseType_t xHigherPriorityTaskWoken, xResult;
if(xPortIsInsideInterrupt() == pdTRUE) {
// Send an event to the main radio task
xHigherPriorityTaskWoken = pdFALSE;
xResult = xEventGroupSetBitsFromISR(xRadioTaskEventObject, 1,
&xHigherPriorityTaskWoken);
// If the radio task is higher-priority than the context we're currently
// running from, we should yield now and run the radio task.
//
if ( xResult != pdFAIL )
{
portYIELD_FROM_ISR(xHigherPriorityTaskWoken);
}
}
else {
xResult = xEventGroupSetBits(xRadioTaskEventObject, 1);
//
// If the radio task is higher priority than the context we're currently
// running from, we should yield now and run the radio task.
//
if ( xResult != pdFAIL )
{
portYIELD();
}
}
}
}
这是FreeRTOS发送一个事件标志组，xPortIsInsideInterrupt这个函数判断是否在中断中，进而调用判断是否调用FromISR结尾的api，下面看下原理
static portFORCE_INLINE BaseType_t xPortIsInsideInterrupt( void )
{
uint32_t ulCurrentInterrupt;
BaseType_t xReturn;
/* Obtain the number of the currently executing interrupt. */
__asm
{
mrs ulCurrentInterrupt, ipsr
}
if( ulCurrentInterrupt == 0 )
{
xReturn = pdFALSE;
}
else
{
xReturn = pdTRUE;
}
return xReturn;
}读IPSR寄存器，0表示当前没有中断在运行，非0表示正在运行的中断号，即处于中断中，所以要用FromISR结尾的api
