The Tprof tool is a timer profiler that identifies what code is running on the CPU during a user-specified time interval.
Tprof 工具是一个计时器剖析器，可以识别出在用户指定的一个时间间隔内哪些代码在 CPU 上运行。
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DMA can run constantly or can be triggered by exterior interruption (INT3-0), interior interruption (timer and serial port), at the end of transfers, send interruption signal to CPU.