本文内容整理自西安交通大学软件学院李晨老师的课件,仅供学习使用,请勿转载

计算机组成原理系列笔记汇总：计算机组成原理笔记及思维导图汇总附复习建议_Qlz的博客-CSDN博客

文章目录

本章思维导图

输入输出思维导图

External Devices

I/O Speed: bytes transferred per second(from mouse to display: 10-to-million)

Disk drive

• Contain two types of electronics
• One type for exchanging data, control and status signals with an I/O module
• The other for controlling the disk read/write mechanism

I/O Modules

Function of I/O Module

• Control & Timing
• CPU ~ I/O Communication
• Device ~I/O Communication
• Memory ~ I/O communication
• Data Buffering
• Error Detection

I/O Steps

• CPU checks I/O module and device status
• I/O module returns status
• If ready, CPU requests data transfer
• I/O module gets data from device
• I/O module transfers data to CPU
  • Programmed-I/O
  • Interrupt-Driven I/O
  • DMA/Channel

I/O Communication

• Command decoding:
  • Read sector, Seek track, Scan ID
  • Which blocks can be read or written.
• Data exchange
  • External data I/O module buffer through local bus
  • I/O module buffer CPU/memory through system bus
• Status reporting
  • Busy, ready, error, etc
• Address recognition
  • Recognize each peripheral

Data Buffering

• Adapt peripherals to CPU or main memory in their velocities
• CPU/DRAM←→\leftarrow \rightarrow←→ I/O buffer
• I/O buffer ←→\leftarrow \rightarrow←→ peripherals

Error Detection

• An I/O modular is often responsible for error detection and reporting errors to CPU
• One class of errors is hardware failure
  • Mechanical or electrical
  • E.g.: paper jam, bad disk track
• Another class of errors is transmitting errors
  • Bit errors
  • Data losses

I/O Module Decisions

• Support multiple or single device
• Hide or reveal device properties to CPU
• Control device functions or leave for CPU
• Also O/S decisions
  • e.g. Unix treats everything it can as a file

Input Output Modes

• Programmed
• Interrupt driven
• Direct Memory Access (DMA)
• I/O Channel
• I/O processor

Programmed I/O

• With programmed I/O, data are exchanged between the CPU and I/O modular

• CPU has direct control over I/O in a program

  • Sensing status
  • Read/write commands
  • Transferring data

• CPU waits for I/O module to complete operation when it issues an I/O command

• Wastes CPU time

process

• CPU encounters an I/O instruction
• CPU executes it, by sending a command to I/O modular, and waits for the I/O modular ready
• I/O modular performs the command and then set the appropriate bit in the I/O status register
• CPU periodically checks the status bit until it find the operation completed

I/O Commands

• CPU issues address
  • Identifies module & device ( if >1 per module)
• CPU issues commands: 4 commands
  • Control - telling module what to do
    • e.g. rewind, open disk drive, etc
  • Test - check status
    • e.g. power? Error?
  • Read/Write
    • Module transfers data via buffer from/to device

Addressing I/O Devices

• Under programmed I/O data transfer is very like memory access (CPU viewpoint)
• Each device given unique identifier
• CPU commands contain identifier (address)

I/O Mapping

不太明白

• Memory mapped I/O
  • Devices and memory share an address space
    • 0xxxxxx, 1xxxxxx
  • I/O looks just like memory read/write
  • No special commands for I/O
    • Large selection of devices available
• Isolated I/O
  • Separate address spaces
  • Need I/O or memory select lines
  • Special commands for I/O
    • Limited set

Summary

• Advantage:
  • Simple: processor is totally in control and does all
• Disadvantage:
  • Polling overhead can consume a lot of CPU time
• Solution: use exception mechanism to help I/O. Interrupt program when I/O ready, return when done with data transfer

Interrupt Driven I/O

• Overcomes CPU waiting
• No repeated CPU checking of device
• I/O module interrupts when ready

Interrupt Driven I/O Basic Operation

• CPU issues read command, and then do other things
• 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 through bus
• At last, CPU recover previous work

CPU Viewpoint

• Issue read command
• Do other work
• Check for interrupt at end of each instruction cycle
• If interrupted:-
  • Save context (registers)
  • Process interrupt
    • Fetch data & store
  • Restore context
• Continue previous work

I/O Module Viewpoint

• Receive a READ command from CPU
• Detect the state of the peripheral
• Read data from the peripheral, put it into registers
• Signal an interrupt to CPU
• Wait until its data are requested by CPU
• Place the data on the data bus

Design Issues

How do you identify the module issuing the interrupt

• Multiple interrupt lines
  • Different line for each module, Limits number of devices
• Software poll
  • CPU asks each module in turn through interrupt-service subroutine
    • Command + address of I/O module
    • Read addressable status register contained in each I/O module
    • CPU branches to the device service routine
  • Slow (time consuming)
• Daisy chain or Hardware poll Bus
  • All I/O modules share a common interrupt request line
  • Once CPU senses an interrupt, Interrupt Acknowledge sent down a chain
  • Module responsible places vector (address, id) on bus
  • CPU uses vector to point to an appropriate device-service routine
  • Referred to as vectored interrupt
• Arbitration (vectored)
  • Module must claim the bus before it can raise interrupt
  • CPU detects the interrupt, respond it through interrupt acknowledge line.
  • I/O module places vector on the data bus
    • e.g. PCI & SCSI

How do you deal with multiple interrupts

• With multiple lines, Each interrupt line has a priority
  • Higher priority lines can interrupt lower priority lines
• With software polling, the order in which modules are polled determines their priority
• With daisy, the order of modules on the daisy determines their priority

Direct Memory Access

Drawbacks of programmed and interrupt-driven I/O

• Programmed I/O needs to occupy all CPU time
• Interrupt driven I/O still requires active CPU intervention, though more efficient CPU usage than Programmed I/O (transfer rate is lower)
• In both modes, data transfer must traverse CPU
  • Transfer rate is limited
  • CPU is tied up
• When large volumes of data are transferred, DMA is a more efficient technique

What is DMA

• External to the CPU
• Additional Module (hardware) on bus
• DMA controller takes over from CPU for I/O
  • Transfer blocks of data to or from memory without CPU intervention
• In fact, DMA is also an I/O module
• Act as a master on the bus
• Memory system acts like slave
• Manage byte-word conversion
• Priority: DMA > CPU

Three modes of data transfer between CPU and DMA

• Block transfer mode (Monopolistic mode)
  • 当DMA传送数据的时候，CPU不能使用总线
  • An entire block of data is transferred in one contiguous sequence
  • If DMA transfers data, CPU be disabled for a duration until DMA release bus
  • Useful for loading an programs or data files into memory
• Cycle stealing mode
  • DMA与CPU交替传输数据
  • DMA uses the bus only when CPU does not need it or forcing CPU to suspend operation temporarily
  • DMA transfer one word of data, then release bus
  • DMA interleaves instructions and data transfers
• Transparent mode (alternate mode)
  • DMA与CPU分别占用时钟的上升沿和下降沿工作
  • DMA and CPU use bus by division time multiplexing
  • Require most time, but most efficient

DMA Structure

数据总线分别于数据计数器，数据寄存器，地址寄存器相连

过程

CPU首先通过Address Lines向地址寄存器发送需要请求的设备地址号，DMA将CPU传来的设备号直接发给I/O，然后CPU通过Data Lines向DMA发送对应的内存地址，存入地址寄存器中保存，CPU通过数据线将数据发送至数据寄存器，DMA将该数据再写入I/O设备中

• Preprocessing: CPU tells DMA controller
  • Read/Write
  • Device address
  • Starting address of memory block for data
  • Amount of data to be transferred
  • CPU carries on with other work
• Data transferring: DMA controller deals with transfer (word by word)
• Postprocessing: DMA controller sends interrupt when finished

DMA Transfer Cycle Stealing

• DMA controller takes over bus for a cycle
• Transfer of one word of data
• Not an interrupt
  • CPU does not switch context
• CPU suspended just before it accesses bus
  • i.e. before an operand or data fetch or a data write
• Slows down CPU but not as much as CPU doing transfer

DMA and Interrupt Breakpoints During an Instruction Cycle

DMA Configurations

Single Bus, detached DMA controller

• Each transfer uses bus twice
  • I/O to DMA then DMA to memory
• CPU is suspended twice

Single Bus, Integrated DMA controller

• Controller may support >1 device
• Each transfer uses bus once
  • DMA to memory
• CPU is suspended once

Separate I/O Bus

• Bus supports all DMA enabled devices
• Each transfer uses bus once
  • DMA to memory
• CPU is suspended once

例题

I/O Channels

• I/O channel is an I/O module with its own processor which can execute I/O program
• I/O program is located in main memory
• In fact, the I/O channel represents an extension of the DMA concept
• Thus, an I/O channel has the ability to execute I/O instructions and control the I/O operations

Functions of I/O Channels

• Receive command from CPU
  • Micro command
• Load I/O program from memory, send commands to device
• Buffer, control and transfer data, provide path for transferring
• Report device status or interrupt

Working Principle

• Master CPU sends I/O command and waits channel and device ready
  • the number of Channel
  • the number of device
  • Entry of channel program
  • Size of data
• Master CPU starts the channel and returns to main program
• The channel executes I/O program to transfer data between memory and device
• When data transfer completed, interrupt CPU

Types of I/O Channels

Channel Capacity/data-transmission rate

• Maximum data transmitted per unit time of channel

Selector channel

• At any one time, only one device is selected to transfer data
• High-speed devices

Multiplexor channel

• Byte multiplexor channel
  • Round robin between devices
  • For a device, only one byte data transferred
  • For low speed devices
• Block multiplexor channel
  • Round robin between devices
  • For a device, K bytes data transferred

Evolution of the I/O Function

• CPU directly control a peripheral
• A control or I/O module is added
  • programmed I/O
• Interrupt-driven I/O
• DMA
  • Device–memory
• I/O channel
  • I/O processor, no local memory
• I/O processor
  • I/O processor + local memory

External Interface

没讲

Connecting devices together

• Point to point
  • Dedicated line between I/O module and external devices
  • E.g. keyboard, printer, modem, etc.
• Point to multi-point
  • external buses
  • External mass storage
  • Multimedia devices (CD-ROMs, video, audio)

Serial or parallel

• Printer, mouse, keyboard, etc.
• Disk, tape, etc.

Write operation from I/O module to a peripheral

• I/O module sends a control signal requesting permission to send data
• The peripheral acknowledges the request
• The I/O module transfers data
• The peripheral acknowledges the receipt of the data

Small Computer Systems Interface (SCSI)

• Standard interface for CD-ROM drive, audio equipment, external mass storage devices
• Parallel interface
  • 8, 16, 32 bit data lines
• Daisy chained local bus, attached to PCI
• Devices are independent
• Devices can communicate with each other as well as host

Key points

• Functions of I/O Module?
• I/O module structure
• Input Output Modes
• What is 82c59a?
• DMA &channel
• SCSI
• Firewire

Vocabulary

• Cycle stealing: 周期窃取
• Interrupt: 中断
• Isolated I/O:分离式I/O
• Memory-mapped I/O:存储映射式I/O
• Multiplexor channel:多路转换通道
• Parallel I/O:并行器I/O
• Peripheral device : 外围设备
• Selector channel:选择通道

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