device 5 management - cu-boulder computer science

Operating Systems: A Modern Perspective, Chapter 5

Slide 5-1

Copyright © 2004 Pearson Education, Inc.

5DeviceManagement


Slide 5-2


Announcements

• Homework Set #1 due Thursday 11 am, see moodle

• copyright issues with lectures• Program Assignment #1 coming soon• Read chapters 4 and 5

– skip sections 4.7, 4.8– skip Sections 5.4, 5.5 for now


Slide 5-3


Determining When I/O is Complete

CPUCPU

DeviceDevice DeviceDevice DeviceDevice

Interrupt Pending

• CPU incorporates an “interrupt pending” flag• When device.busy → FALSE, interrupt pending flag is set• Hardware “tells” OS that the interrupt occurred• Interrupt handler part of the OS makes process ready to run


Slide 5-4


Control Unit with Interrupt (Hardware)

PC = <machine start address>;IR = memory[PC];haltFlag = CLEAR;while(haltFlag not SET) {

execute(IR);PC = PC + sizeof(INSTRUCT);IR = memory[PC];if(InterruptRequest) {

memory[0] = PC;PC = memory[1]

};

couldbe atrapinstr.

memory[1] contains the address of the interrupt handler


Slide 5-5


Examples of Exceptions in Pentium Systems

Class Cause Async/Sync

Return behavior

Trap Intentional exception

Sync always returns to next

instructionFault Potentially

recoverable error

Sync might return to current

instructionAbort nonrecover-

able errorSync never returns

Interrupt signal from I/O device

Async always returns to next

instruction


Slide 5-6


The Trap Instruction Operation

SMode

TrustedCode

trap

User Supervisor

Branch Table

2

3

1

a trap is a “software” interrupt

hardware interrupts behave similarly, an interrupt gives an offset into interrupt vector table


Slide 5-7


Examples of Exceptions in Pentium Systems

Exception Number

Description Exception Class

0 Divide error fault

13 General protection fault

fault

14 Page fault fault

18 machine check abort

32-127 OS-defined Interrupt or trap

128 System call Trap

129-255 OS-defined Interrupt or trap

Exception Table, also called Branch Table orJump Table or Interrupt Vector

non-maskable

OSassigns

maskableinterrupts


Slide 5-8


Maskable Interrupts

• Maskable interrupts can be turned off by CPU before execution of critical instruction sequences– are used by device controllers to talk with CPU

• Nonmaskable interrupts/exceptions is reserved for events such as unrecoverable memory errors and cannot be turned off by the CPU

• Can have multiple interrupt priority levels– high-priority interrupts can preempt execution of a low-

priority interrupt


Slide 5-9


Disabling Maskable Interrupts

saveProcessorState() {for(i=0; i<NumberOfRegisters; i++)

memory[K+i] = R[i];for(i=0; i<NumberOfStatusRegisters; i++)

memory[K+NumberOfRegisters+i] = StatusRegister[i];}

PC = <machine start address>;IR = memory[PC];haltFlag = CLEAR;while(haltFlag not SET) {

execute(IR);PC = PC + sizeof(INSTRUCT);IR = memory[PC];if(InterruptRequest && InterruptEnabled) {

disableInterupts();memory[0] = PC;PC = memory[1]

};

have to reenableinterrupts after done


Slide 5-10


Classes of System Calls Invoked bytrap

• end, abort• load, execute• create, terminate• get attributes, set• wait for time• wait event, signal event• allocate memory, free

Processcontrol

Comm-unications

FileManagement

DeviceManagement

InformationManagement

system call interface

• request device, release• read, write, reposition• get attributes, set• logically attach or

detach devices

• create connection, delete

• send messages, receive• transfer status info• attach remote devices,

detach

• create, delete• open, close• read, write, reposition• get attributes, set

• get time/date, set• get system data, set• get process, file, or

device attributes, set

NoteSimilarity


Slide 5-11


The Device Driver Interface…write(…);…

Device InterfaceDevice Interface

TerminalDriver

TerminalDriver

PrinterDriver

PrinterDriver

DiskDriverDisk

Driver

TerminalControllerTerminalController

PrinterControllerPrinter

ControllerDisk

ControllerDisk

Controller


Slide 5-12


Device Management OrganizationApplication

ProcessApplication

Process

FileManager

FileManager

Device ControllerCommandCommand StatusStatus DataData

Hardware Interface

System Interface

Device-IndependentDevice-Independent

Device-DependentDevice-Dependent

Device Manageror I/O Subsystem

drivers

e.g. write()


Slide 5-13


Device System Call Interface

• Functions available to application programs• Abstract all devices (and files) to a few interfaces• Make interfaces as similar as possible

– Block vs character– Sequential vs direct/random access– Blocking versus Non-Blocking I/O

• blocking system call: process put on wait queue until I/O completes• non-blocking system call: returns immediately with partial number of

bytes transferred, e.g. keyboard, mouse, network sockets– Synchronous versus asynchronous

• asynchronous returns immediately, but at some later time, the full number of bytes requested is transferred

• Device driver implements functions (one entry point per API function)


Slide 5-14


Example: BSD UNIX Driver

open Prepare dev for operationclose No longer using the deviceioctl Character dev specific inforead Character dev input opwrite Character dev output opstrategy Block dev input/output opsselect Character dev check for datastop Discontinue a stream output op


Slide 5-15


Device Independent Function CallTrap Table

funci(…)dev_func_i(devID, …) {// Processing common to all devices…switch(devID) {case dev0: dev0_func_i(…);

break;case dev1: dev1_func_i(…);

break;…case devM: devM_func_i(…);

break;};

// Processing common to all devices…

}


Slide 5-16


Overlapping the Operation of a Device and the CPU

. . .startRead(dev_I, “%d”, x);. . .While(stillReading()) ;y = f(x). . .

. . .read(dev_I, “%d”, x);y = f(x). . .

Variable x Register

Data on device

Device dev_IMemory CPU


Slide 5-17


Overlapping CPU-Controller Operations in a Process

t1 t2 t3 t4 t5 t6 t7 t8 t9

could be non-blocking or asynchronoussystem call

App

I/O Ctlr


Slide 5-18


Overlapping Processing and I/O

t1 t2 t3 t4

App1 makes a blocking or synchronoussystem call

App 1App 2I/O Ctlr


Slide 5-19


Device Manager I/O Strategies

• Underneath the blocking/non-blocking synchronous/asynchronous system call API, OS can implement several strategies for I/O with devices– direct I/O with polling– direct I/O with interrupts– DMA with interrupts


Slide 5-20


Polling I/O Read Operation

read(device, …);

Data

Device Controller

CommandCommand StatusStatus DataData

read driver

write driver

1

2 3 4

5

Hardware Interface

System Interface


Slide 5-21


Interrupt-driven I/O Operation

read(device, …);

Data

Device Controller

CommandCommand StatusStatus DataData

read driver

write driver

1

2

4

5Hardware Interface

System InterfaceDevice Status Table

DeviceHandlerDeviceHandler

InterruptHandler

InterruptHandler

6

7

8b

9

8a3


Slide 5-22


Driver-Kernel Interface

• Drivers are distinct from main part of kernel• Kernel makes calls on specific functions,

drivers implement them• Drivers use kernel functions for:

– Device allocation– Resource (e.g., memory) allocation– Scheduling– etc. (varies from OS to OS)


Slide 5-23


DMA with Interrupts Example

CPU

MemoryDMA/bus/interruptController

DiskController

CPU/Memory Bus

1. device driver toldto transfer bytes fromdisk to memory2. dev driver informsdisk controller

5. DMAsends eachbyte tomemory6. DMAinterruptsCPU whendone

I/O Bus

3. disk controllerinitiates DMA4. disk controller sendseach byte to DMAcontroller


Slide 5-24


Handling Interrupts

int read(…) {// Prepare for I/Osave_state(J);out dev#

// Done (no return)}

Device driver J

Device ControllerDevice Controller

Interrupt HandlerInterrupt Handler

void dev_handler(…) {get_state(J);

//Cleanup after opsignal(dev[j]);return_from_sys_call();

}

Device interrupt handler J

J

Device status table


Slide 5-25


Handling Interrupts(2)

int read(…) {…out dev#

// Return after interruptwait(dev[J});return_from_sys_call();

}

Device driver J

Device ControllerDevice Controller

Interrupt HandlerInterrupt Handler

void dev_handler(…) {//Cleanup after opsignal(dev[j]);

}

Device interrupt handler J

device 5 management - cu-boulder computer science

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