指令运行周期的开始发生。
Activity is a unit of instruction execution, and is the building block of a process.活动(activity)是指令执行的一个单元,它是一个流程的基本组成部分。
In other words, SOFTWARE interrupts always occur at the beginning of an instruction execution cycle.换句话说,软件中断常常在指令运行周期的开始发生。