lo Structure JO结构 After l/O starts, control returns to user program only upon l/O completion 在ⅣO开始之后,仅当O完成之后控制才返回用户程序 wait instruction idles the CPU until the next interrupt 等待指令空转cPU直至下一个中断 wait loop( contention for memory access)等候循环 At most one I/o request is outstanding at a time, no simultaneous I/o processing每一时刻最多一个O请求,无并行o处理 After lo starts, control returns to user program, without waiting for I/o completion.在O开始之后,不等O完成控制就返回用户程序 System call- request to the operating system to allow user to wait for o completion系统调用-请求操作系统允许用户等待lO完成 Device-status table contains entry for each l/o device indicating its type, address, and state设备状态表包括每个o设备的类型、地址和状态 Operating system indexes into o device table to determine device status and to modify table entry to include interrupt操作系统引用设备 状态表以确定设备状态并修改表入口加入中断 Applied Operating System Concepts 2.7Applied Operating System Concepts 2.7 I/O Structure I/O结构 • After I/O starts, control returns to user program only upon I/O completion. 在I/O开始之后，仅当I/O完成之后控制才返回用户程序 – wait instruction idles the CPU until the next interrupt 等待指令空转CPU直至下一个中断 – wait loop (contention for memory access).等候循环 – At most one I/O request is outstanding at a time, no simultaneous I/O processing.每一时刻最多一个I/O请求，无并行I/O处理 • After I/O starts, control returns to user program， without waiting for I/O completion. 在I/O开始之后，不等I/O完成控制就返回用户程序 – System call – request to the operating system to allow user to wait for I/O completion.系统调用-请求操作系统允许用户等待I/O完成 – Device-status table contains entry for each I/O device indicating its type, address, and state.设备状态表包括每个I/O设备的类型、地址和状态 – Operating system indexes into I/O device table to determine device status and to modify table entry to include interrupt.操作系统引用设备 状态表以确定设备状态并修改表入口加入中断