In most RTOS, the timer interrupt service routine (ISR) executes at every time tick.
在一般的嵌入式实时操作系统中，时钟中断服务程序在每个时钟节拍工作。
In most practical application, context switch doesn't happen at some time tick, so sometime the execution of timer ISR is useless and wastes CPU time.
在实际应用中，并不是每个时钟节拍都有任务调度，所以有很多时钟中断服务程序的工作是多余的，浪费了CPU资源。
In most practical application, context switch doesn't happen at some time tick, so sometime the execution of timer ISR is useless and wastes CPU time.
在实际应用中，并不是每个时钟节拍都有任务调度，所以有很多时钟中断服务程序的工作是多余的，浪费了CPU资源。
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