4 Device Management

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2008 Chapter-8 L6: "Embedded Systems - Architecture, Programming

and Design" , Raj Kamal, Publs.: McGraw-Hill, Inc.1

REAL TIME OPERATING SYSTEMS

Lesson-6:Device Management Functions


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1. Device manager functions1. Device manager functions


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Device Driver ISRsDevice Driver ISRs

Number of device driver ISRs in a

system,

Each device or device function having s a

separate driver, which is as per its

hardware


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Software that manages the device drivers ofeach device

Provides and executes the modules for

managing the devices and their driversISRs.

Effectively operates and adopts appropriatestrategy for obtaining optimal performancefor the devices.

Coordinates between application-process,driver and device-controller.

Device managerDevice manager


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Process sends a request to the driver by an

interrupt; and the driver provides the actions

by executing an ISR.

Device manager polls the requests at the

devices and the actions occur as per their

priorities.

Manages IO Interrupts (requests) queues.



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Creates an appropriate kernel interface and

API and that activates the control register

specific actions of the device. [Activates

device controller through the API and

kernel interface.]



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Manages the physical as well as virtual

devices like the pipes and sockets through a

common strategy.


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and Design" , Raj Kamal, Publs.: McGraw-Hill, Inc.

8

Device management has three standardDevice management has three standard

approachesapproaches

Three types of device drivers:

(i) Programmed I/Os by polling from eachdevice its the service need from each

device. Interrupt(s) from the device drivers device-

ISR and

(iii) Device uses DMA operation used bythe devices to access the memory.

Most common is the use of device driverISRs


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9

Device Manager FunctionsDevice Manager Functions

Device Detection and Addition

Device Deletion

Device Allocation and

Registration

Detaching and Deregistration


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Restricting Device to a specific process

Device Sharing

Device control

Device Access Management

Device Buffer Management

Device Queue, Circular-queue or blocks of

queues Management


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Device drivers updating and upload of new

device-functions

Backup and restoration


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Device TypesDevice Types

char devices and

block devices


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2.2. Set of Command Functions for theSet of Command Functions for the

Device ManagementDevice Management


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Commands for DeviceCommands for Device

create

open

write read

ioctl

close and

delete


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ioctl Command for Deviceioctl Command for Device

(i) Accessing specific partition information

(ii) Defining commands and control

functions of device registers

(iii) IO channel control


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Three arguments in ioctl ( )Three arguments in ioctl ( )

First Argument: Defines the chosen device and

its function by passing as argument the device

descriptor (a number), for example, fd or sfd

Example is fd = 1 for read, fd = 2 for write. Second Argument: Defines the control option or

uses option for the IO device, for example, baud

rate or other parameter optional function

Third Argument: Values needed by the definedfunction are at the third argument


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ExampleExample

Status = ioctl (fd, FIOBAUDRATE, 19200)

is an instruction in RTOS VxWorks.

fdis the device descriptor (an integer

returned when the device is opened)

FIOBAUDRATE is the function that takes

value = 19200 from the argument.

This at configures the device for operationat 19200-baud rate.


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3. Device Driver ISR functions3. Device Driver ISR functions


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ISR functionsISR functions

intlock( ) to disable device-interrupts

systems,

intUnlock ( ) to enable device-interrupts,

intConnect( ) to connect a C function to an

interrupt vector

Interrupt vector address for a device ISR

points to its specified C function. intContext ( ) finds whether interrupt is

called when an ISR was in execution


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4. Unix OS functions4. Unix OS functions


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UNIX Device driver functionsUNIX Device driver functions

Facilitates that for devices and files have an

analogous implementation as far as

possible.

open ( ),

close ( ),

read( ),

write ( ) functions analogous to a file open,close, readand write functions.


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APIs and kernel interfaces in BSD (BerkleyAPIs and kernel interfaces in BSD (Berkley

sockets for devices)sockets for devices) open,

close,

read

write


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inin--kernel commandskernel commands

(i) select( ) to check whther read/write will

succeed and then select

(ii) ioctl ( )

(iii) stop ( ) to cancel the output activity

from the device.

(iv) strategy ( ) to permit a blockread or

write or character read or write


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SummarySummary


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We learntWe learnt

Device Manager initializes, controls, anddrives the physical devices and virtual

devices of the system.

Main classes of devices are char devicesand block devices.

Device driver functions may be similar to

file functions, open, read, lseek, write and

close


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End of Lesson 6 of Chapter 8End of Lesson 6 of Chapter 8

4 Device Management

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