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MindMap Gallery Computer operating system—input and output management

Computer operating system—input and output management

This article is about some basic concepts of computer operating system IO, with a detailed introduction and comprehensive description. I hope it can help interested friends learn.

Edited at 2023-12-01 15:12:41

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Computer operating system—input and output management

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Outline

Process description and control
- 7
Wyatt9956

I/O management

I/O management overview

I/O device classification

Classified by usage characteristics

Human-computer interaction external devices

storage device

Network communication equipment

Transmission rate

low speed device

medium speed equipment

high speed equipment

information exchange unit

block device

Fast transmission and addressable

character device

The transmission is slow, not addressable, and uses an interrupt-driven approach.

I/O controller

The main function

Accept and identify instructions issued by the CPU (control register)

Report the status of the device to the CPU (status register)

Data exchange (data register temporary data)

Address recognition (implemented by I/O logic)

composition

Interface between CPU and controller (implementing communication between controller and CPU)

I/O logic (responsible for identifying commands issued by the CPU and issuing commands to the device)

Interface between controller and device (implementing communication between controller and device)

Two register addressing methods

Memory mapped I/O

Unified addressing of registers and memory in the controller

The controller can be operated using instructions that operate on memory

Registers in the controller are individually addressed

Special instructions need to be set to operate the controller

I/O control mode

Program direct control

Disadvantages: CPU and I/O devices can only work serially, resulting in extremely low CPU utilization.

Interrupt driven mode

Allow I/O devices to actively interrupt the operation of the CPU and request services, This frees up the CPU so that it can continue to do other useful work after sending read commands to the I/O controller.

Disadvantages: Since each word of data must be transferred between the memory and the I/O controller through the CPU As a result, the interrupt-driven method still consumes more CPU time.

DMA (direct memory access) method

Establish a direct data path between I/O devices and memory to fully access the CPU

Features

The basic unit is the data block

The data transferred is sent directly from the device to the memory, or vice versa

CPU intervention is only required when transferring the beginning and end of one or more consecutive data blocks The transfer of the entire block of data is completed under the control of the DMA controller

channel mode

The I/O channel is a processor specifically responsible for input/output. It is a development of the DMA method, which can further reduce CPU intervention. That is, the intervention of reading (or writing) a data block is reduced to the intervention of reading (or writing) a group of data blocks and related control and management. At the same time, it can realize the parallel operation of CPU, channel and I/O device.

The channel instruction type is single and does not have its own memory. The channel program executed by the channel is placed in the memory of the host. The channel shares memory with the CPU.

I/O software hierarchy

User level I/O software

Interface implemented for user interaction

device independence software

Perform operations common to all devices

Distribution and recycling of equipment

Map logical device names to physical device names

Protect your device

Buffer management

error control

Provides logical blocks of uniform size that are independent of the device, shielding differences in information exchange unit size and transmission rate between devices

Provide a unified interface to the user layer

device driver

Related to hardware, responsible for specifically implementing the operating instructions issued by the system to the device.

Interrupt handler

Used to handle interrupt related matters

hardware

Consists of a mechanical component (the device itself) and an electronic component (the device controller/adapter)

Device Controller Functions

Recognize or accept commands from the CPU or channel

Realize data exchange

Discover and log status information about the device or itself

Device address identification

I/O core subsystem

I/O scheduling concepts

Determine a good order to perform I/O requests

Caches and buffers

single buffer

Device - (T) - Buffer - (M) - Workspace - (C) - Processing

When the buffer is full, data will be sent to the work area. When the work area is full, the buffer will be empty at the same time.

Assume the initial state, the work area is full and the buffer is empty: The average time taken to process a piece of data is Max (C, T) M

double buffering

Assume the initial state, buffer 1 is full, buffer 2 is empty, and the work area is empty: The average time taken to process a piece of data is Max (T, C M)

Buffer 1 is full and data is being loaded into buffer 2. At this time, data can be fetched from buffer 1. Data can only be retrieved when the buffer is full

circular buffer

Multiple buffers are linked into a circular queue, with the in pointer pointing to the first empty buffer and the out pointer pointing to the first full buffer.

buffer pool

three queues

empty buffer queue

input queue

output queue

Four working buffers

Work buffer used to accommodate input data, work buffer used to extract input data

Work buffer used to contain output data, work buffer used to extract output data

Buffer versus cache

Buffer concept

Generally use memory as a buffer

Ease the speed conflict between the CPU and the device and reduce the frequency of interrupts to the CPU Solve the problem of data granularity mismatch and improve the parallelism between CPU and I/O devices

Features

When the data in the buffer is not empty, data cannot be flushed into the buffer and data can only be transferred out of the buffer.

When the buffer is empty, data can be rushed into the buffer, but the buffer must be filled before data can be transferred out of the buffer.

Equipment distribution and recycling

Factors that should be considered

intrinsic properties

Exclusive devices, shared devices, virtual devices (SPOOLing)

allocation algorithm

First come, first served, higher priority first, shorter tasks first

safety

Safe distribution method

Unsafe allocation method

Static allocation and dynamic allocation

Dynamic allocation is performed according to execution needs during process execution.

Data structures in device allocation management

Device Control Table (DCT)

Each device corresponds to a DCT, key fields: type/identifier/status/pointer to COCT/waiting queue pointer

Controller Control Table (COCT)

Each controller corresponds to a COCT, key fields: status/pointer to CHCT/waiting queue pointer

Channel Control Table (CHCT)

There is a pointer to the connected controller table, and the head and tail pointers of the PCB queue of the process waiting for the channel.

System Device Table (SDT)

Record the status of all devices in the entire system, each device corresponds to an entry

Key fields

Device type/identifier/DCT/driver entry

One channel controls multiple controllers, one controller controls multiple devices

Device Allocation Steps

1. Find SDT based on the physical device name requested by the process 2. Find DCT and allocate equipment according to SDT 3. Find the COCT according to the DCT and assign the controller 4. Find CHCT and assign channels based on COCT

Only when the device, controller, and channel are all successfully allocated, the device will be considered successfully allocated, and then the I/O device can be started for data transmission.

shortcoming

Users must use the "physical device name" when programming. If a physical device is changed, the program will not run. If the requested device is busy, the process must wait even if there are other devices of the same type in the system.

Improvements to the device allocation step

Users use logical device names to apply for devices when programming, and the OS is responsible for mapping from logical device names to physical device names.

Logical device table settings

There is only one LUT in the entire system: the logical device names used by each user are not allowed to be repeated.

One LUT per user: the logical device name of each user can be repeated

SPOOLing

offline technology

Peripheral controller Higher-speed equipment—tape

Function: Alleviate the speed conflict between the device and the CPU, and realize pre-input and slow output.

SPOOLing

Simulating offline technology using software methods

input wells and output wells

storage area

input process and output process

input buffer and output buffer

input buffer

Temporarily store data sent from the input device

output buffer

Temporarily store data from the output well

Shared printer

Use SPOOLing technology to "virtualize" exclusive printers into shared printers