COA课件07

branching
处理
分支
suspending
break point
断点
挂起
resuming
恢复
(5) Resuming User Program (1)Do User Program ……(2)Suspending (3)Branching (4) Processing
Interrupt Driven I/O Basic Operation(read)
CPU<—I/O module<—external Device
data
data
• Write???
I/O Module Diagram
Page204
控制信息 状态信息
I/O Module Decisions
• Hide or reveal device properties to CPU • Support multiple or single device • Control device functions or leave for CPU • Also O/S decisions
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• 0. CPU issuses I/O command to I/O module, then CPU does something else…. • 1. After I/O module prepares data, issues an interrupt request signal to CPU • 2. CPU finishes execution of the current instructions, CPU checks interrupt request. • 3. The CPU makes sure of an interrupt , and sends an acknowledge signal to module( allows the module to remove its interrupt signal & to sends interrupt number to CPU) • 4. The CPU saves information of current program to stack for resuming it. The important information is PSW(running status of current program) & PC(the address of next instruction)
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• CPU issues read command • I/O module gets data from peripheral whilst CPU does other work • I/O module interrupts CPU • CPU requests data • I/O module transfers data
• Isolated I/O 独立I/O
—Separate address spaces —Need I/O or memory select lines —Special commands for I/O – Limited set 只有少数几种I/O命令
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※§7.4 Interrupt Driven I/O
I/O module Viewpoint
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• Receives a read command from CPU • Then, proceeds to read data in from an associated peripheral • Once data in its data register , signals an interrupt request to CPU • Then waits until its data requested by CPU, places its data on the data bus • Then ready for another I/O operationProgLeabharlann ammed I/O – detail
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• CPU requests I/O operation • I/O module performs operation • I/O module sets status bits • CPU checks status bits periodically周期性地 • I/O module does not inform CPU directly • I/O module does not interrupt CPU • CPU may wait or come back later
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• Overcomes CPU waiting • No repeated CPU checking of device • I/O module interrupts when ready
Transfer of Control via Interrupts
Page61
processing
I/O Mapping
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• Memory mapped I/O 存储映射式I/O
—Devices and memory share an address space —I/O looks just like memory read/write —No special commands for I/O – Large selection of memory access commands available
Simple interrupt processing
Hardware
Device controller or other system hardware issue an interrupt Processor finishes execution of current instruction Processor signals acknowledgment of interrupt Processor pushes PSW & PC onto control stack Processor loads new PC value based on interrupt
I/O Steps(Read)
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• CPU checks I/O module device status • I/O module returns status • If ready, CPU requests data transfer • I/O module gets data from external device • I/O module transfers data to CPU
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software ISR
Save remainder of process state information
Process interrupt
Restore process state information
Restore old PSW & PC
※ Interrupt Processing(1)
CPU Viewpoint
Page208
• Issue read command, then do other work • Check for interrupt at end of each instruction cycle • If interrupted: —Save context (e.g.PC and registers) —Process interrupt –Fetch data & store —Restore context and resume interrupted work
直接存储器存取
§7.3 Programmed I/O
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• CPU has direct control over I/O
—Sensing status 检查设备状态 —Read/write commands 发送读/写命令 —Transferring data 传送数据
• CPU waits for I/O module to complete operation • Wastes CPU time
William Stallings Computer Organization and Architecture 6th Edition
Chapter 7 Input/Output
The Computer
外设 通信线路
I/O
主存
CPU
Input/Output Problems
Page196
• Wide variety of peripherals
—With various methods of operation —At different transfer rate —In different data formats
• often slower than CPU and RAM • Need I/O modules
I/O Module(Two major functions)
控制 状态
Page198
数据
Control bus
变换器
Typical I/O Data Rates
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千兆位以太网 图形显示器 硬盘 以太网 图形显示
扫描仪
激光打印机 软盘 调制解调器 鼠标 键盘
§7.2 I/O Module Function
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• Control & Timing 控制和定时 • CPU Communication 处理器通信 －command decoding 命令译码 －data transfer 数据传输 －status reporting 状态报告 －address recognition 地址识别 • Device Communication 设备通信 • Data Buffering 数据缓冲 • Error Detection 检错