device management

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Device ManagementDevice ManagementDevice ManagementDevice Management

• The von Neumann Architecture• System Architecture• Device Management

•Polling•Interrupts•DMA

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Von Neumann Von Neumann ArchitectureArchitecture


Born 28 December 1903, Budapest, Hungary; Died 8 February 1957, Washington DC; Brilliant mathematician, synthesizer, and promoter of the stored program concept which became the prototype of most of its successors - the von Neumann Architecture

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bus

cpumemorydevicedevice

Machine has a fixed set of electronic parts

Actions are determined by a program stored in the computer memory.

Instructions and Data

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Prior to this time programming was done with switches & plugboards

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bus

cpu

address linesdata lines

ALUControlUnit

General Purpose&

Status Registers

operatingsystems The CPU and the BusThe CPU and the Bus

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cpu

ALUControl

Unit

General Purpose&

Status Registers

fetch unit

decode unit

execution unit

instruction reg

program ctraddress

instruction

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bus

Memory unit

memory MAR

MDR

Command

Memory Address register

Memory Data register

operatingsystems The Memory UnitThe Memory Unit

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bus

Memory unit

memoryMAR

MDR

CMDREG

Writing to MemoryWriting to Memory

Address to write toData to write

Write command

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Memory Address register

Memory Data register

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DevicesDevicesDevicesDevices

In a Unix system, every device is treated just like a file.In fact, all devices have a file name in the file system

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Files that represent devices are in the /dev directory

$ ls –C /dev

You can list the terminal device you are attached to

$ tty

You can copy a file to the terminal

$ cp myFile.txt /dev/tty2

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Block Devices

Stores data in fixed size blocks.Blocks can be read/written independently

Character DevicesDelivers or accepts a stream of characters.

DevicesDevicesDevicesDevicesoperatingsystems

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Do an ls command on a terminal device

$ ls –al /dev/ttyp1

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crw - - w - - - - 1 debry tty 4, 1 Aug 4 4:18 /dev/tty1

A character device

this is usually wherethe file size goes.What’s up?

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Do an ls command on a terminal device

$ ls –al /dev/tty1

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A character device

The i-node in this case does notcontain the address of a disk block,but the address of a device driver.

In this case, 4 is the “address” of thedevice driver, and 1 is an argumentpassed to the device driver.

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A character device

only the terminal owner can read from the terminal.

any other terminal user can write to the terminal

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At the API, all devices support a common set of commands:

openclosereadwrite ...

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For example, to read from a tape drive, you mightwrite code that looks like the following:

int fd;fd = open(“dev/tape”,O_RDONLY);lseek(fd, long (4096, SEEK_SET);n = read(fd, buffer_length);close(fd);

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Note that all devices do not support all of thefile system commands. For example, you cannotdo a seek on a terminal.

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I/O LayersI/O LayersI/O LayersI/O Layers

User ProgramUserSpace

Operating System

DeviceDriver

KernelSpace

DeviceController

DeviceDriver

DeviceController

DeviceDriver

DeviceController

API

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Standard I/F

openclosereadwriteioctl

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Layers of the I/O system and the main

functions of each layer

Layers of the I/O system and the main

functions of each layer

User Process

Device Independent Layer

Device Dependent Layer

Interrupt Handler

LOGICAL I/O: open, read, write, …

Naming, protection, blocking, allocation

Write to device registers, read statusDri

ver

Wake up driver when I/O completes

Device Controller

Perfom the physical I/O operationdata status command

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Device ControllersDevice ControllersDevice ControllersDevice ControllersI/O devices have two major components:

A mechanical component An electronic component

The electronic component is the device controller. It may be able to handle multiple devices

Controller's tasksconvert serial bit stream to block of bytesperform error correction as necessarymake data available to main memorycontinuously monitor the state of the deviceControl the device

I/O devices have two major components:A mechanical component An electronic component

The electronic component is the device controller. It may be able to handle multiple devices

Controller's tasksconvert serial bit stream to block of bytesperform error correction as necessarymake data available to main memorycontinuously monitor the state of the deviceControl the device

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Control and statusregisters

Data buffer

Device Controller

I/O Bus

Put an address on the address line of the I/O bus the address selects the device

put the command to be executed on the control line

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A Device Controller A Device Controller Example:Example:

Reading Data From DiskReading Data From Disk

A Device Controller A Device Controller Example:Example:

Reading Data From DiskReading Data From Disk

CPU Controller

buffer

Memory

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1. The cpu issues a read command to the disk controller

read

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Reading Data From DiskReading Data From DiskReading Data From DiskReading Data From Disk

CPU Controller Memory

1. The cpu issues a read command to the disk controller2. The disk controller reads the required data from the device and stores it in it’s internal buffer

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||||||||||||

buffer

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CPUController

buffer

Memory

1. The cpu issues a read command to the disk controller2. The disk controller reads the required data from the device and stores it in it’s buffer3. The controller sends an interrupt to the cpu indicating that data is ready to be read

INT

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CPU Controller

buffer

Memory

1. The cpu issues a read command to the disk controller2. The disk controller reads the required data from the device and stores it in it’s buffer3. The controller sends an interrupt to the cpu indicating that data is ready to be read4. The cpu reads one byte of data from the controller buffer

reg

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a

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CPU Controller

buffer

Memory

1. The cpu issues a read command to the disk controller2. The disk controller reads the required data from the device and stores it in it’s buffer3. The controller sends an interrupt to the cpu indicating that data is ready to be read4. The cpu reads one byte of data from the controller buffer5. The cpu writes the byte to memory. This process continues until all data is transferred

reg

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Using Direct Memory Using Direct Memory AccessAccess


CPU Controller

buffer

MemoryDMA Controller

A DMA controller is like a mini-cpu. It can readAnd write data to memory without involving

The CPU.

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CPU Controller

buffer

Memory

1. The cpu programs the dma controller, giving it a beginning address in memory, a byte count,and a command to execute. It also sends a read command to the disk controller. The cpu can now go on and do other work.

DMA Controller

read

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pgm

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CPU Controller

buffer

Memory

1. The cpu programs the dma controller, giving it a beginning address in memory, a byte count, and a command to execute. It also sends a read command to the disk controller.

2. The disk controller reads the data from the disk and stores it in its data buffer, just as it did before.

DMA Controller

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CPU Controller

buffer

Memory



3. The DMA controller sends a command to the disk controller requesting abyte of data.

DMA Controller

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CPU Controller

buffer

Memory




4. The disk controller sends a byte of data to the dma controller

DMA Controller

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CPU Controller

buffer

Memory




4. The disk controller sends a byte of data to the dma controller5. The dma controller writes the byte to memory.

DMA Controller

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CPU Controller

buffer

Memory

6. The disk controller sends an acknowledgement signal to the dma controller. This continues until all of the data has been transferred. All of this happens without

the cpu being involved. When all of the data has been transferred, then the cpu is

interrupted.

DMA Controller

ack

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int

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Memory-Mapped I/OMemory-Mapped I/OMemory-Mapped I/OMemory-Mapped I/O

Primarymemory

device 0

device 1

device 2

memory addresses

device addresses

Traditional approachuses special I/Oinstructions to getat device registers

copy_in R3, 0x012, 4

Copy the contents of register 4 in the device at address 012into cpu register 3

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Memory-Mapped I/OMemory-Mapped I/OMemory-Mapped I/OMemory-Mapped I/O

Primarymemory

device 0

device 1

device 2

memory addresses

With memory mapped I/O no special instructions are needed. Device registers are mapped by the hardware into memory addresses.

Load R3, 0xFFF0124

Load register 3 from memoryAddress 0xFFF0124

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Single Bus ArchitectureSingle Bus ArchitectureSingle Bus ArchitectureSingle Bus Architecture

bus


All addresses and data go on the same bus

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Multiple Bus ArchitectureMultiple Bus ArchitectureMultiple Bus ArchitectureMultiple Bus Architecture

bus


All device addresses and data go on another bus

The cpu uses one bus to access memory

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Polling vs. InterruptsPolling vs. InterruptsPolling vs. InterruptsPolling vs. Interruptsoperatingsystems

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PollingPollingPollingPolling

Because there is a tremendous difference in speed between an I/O device and the computer, the computer must wait until the device is ready to process the next byte of data.

InstructionRegister

AccumulatorStatus

Register

Control lines and address lines

Data linesStatus lines

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ExampleExampleExampleExample

InstructionRegister

AccumulatorStatus

Register

Control lines and address lines

Data linesStatus lines

character to be printed

print instructiondevice address

characterprint

printed!

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PollingPollingPollingPolling

Issue WriteCommand

Load characterinto accumulator

Is theprinterdone?

noLoad characterinto accumulator

yes

What is wrong with this approach ?

If the printer can print 100 charactersa second, then it takes 10ms to printeach character. Thus this polling loopruns for 10 ms between each character.Clear the

status register

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Direct I/O with PollingDirect I/O with PollingDirect I/O with PollingDirect I/O with Polling

User Program

Operating System

DeviceDriver

KernelSpace

DeviceController

Device Interface (API)

UserSpace

1. Application issues a read( ) call. The OS blocks the application.

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An example of a device driver using polling

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Direct I/O with PollingDirect I/O with PollingDirect I/O with PollingDirect I/O with Polling2.

User Program

Operating System

DeviceDriver

KernelSpace

DeviceController


UserSpace

2. The device driver queries the status register in the controller to determine whether or not the device is busy. It polls until it is not.

BLOCKED

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Direct I/O with PollingDirect I/O with PollingDirect I/O with PollingDirect I/O with Polling

2.

User Program

Operating System

DeviceDriver

KernelSpace

DeviceController


UserSpace

3. The driver stores a command in the command register of the device controller.

BLOCKED

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User Program

Operating System

DeviceDriver

KernelSpace

DeviceController


UserSpace

4. The controller reads from the device. Since this involves mechanical parts, the read can take some time.

BLOCKED

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User Program

Operating System

DeviceDriver

KernelSpace

DeviceController


UserSpace

BLOCKED

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5. Meanwhile, the device driver queries the status register in the controller to see if the operation is complete. It polls until it is.The CPU cannot be used for anything else.

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User Program

Operating System

DeviceDriver

KernelSpace

DeviceController


UserSpace

7. The device driver reads the data register(s) in the device controller to get the data that has been read from the device.

BLOCKED

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User Program

Operating System

DeviceDriver

KernelSpace

DeviceController


UserSpace

8. The device driver copies the data into user space. The OS unblocks the application program.

BLOCKED

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Interrupts Interrupts Interrupts Interrupts

Handling interrupts on machines that do look-ahead or on super-scalar machines is quite complicated. This discussion is

simplified.

bus

cpu memoryInterruptcontroller

device

Device finishes it operation.It writes its status to theInterrupt controller

cpu

The Interrupt controllerissues the interrupt to theCPU. The interrupt includesa number which is used toindex into an interrupt table.

The CPU stops whatever it is doing,and executes the interrupt handlerpointed to by the interrupt.

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Direct I/O with InterruptsDirect I/O with InterruptsDirect I/O with InterruptsDirect I/O with Interrupts

User Program

Operating System

DeviceDriver

KernelSpace

DeviceController


UserSpace

1. Application issues a read( ) call. The OS blocks the application.

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A Device Driver Using Interrupts

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User Program

Operating System

DeviceDriver

KernelSpace

DeviceController


UserSpace

2. The device driver queries status registers in the device controller to see if the device is busy. If it is, it waits.

BLOCKED

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User Program

Operating System

DeviceDriver

KernelSpace

DeviceController


UserSpace

3. When the device is ready, the device driver stores a command in the command register of the device controller. This starts the device.

BLOCKED

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User Program

Operating System

DeviceDriver

KernelSpace

DeviceController


UserSpace

3. The driver then issues a wait().

BLOCKED

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wait means “I will voluntarily give up the cpuand wait for an interrupt to occur.

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User Program

Operating System

DeviceDriver

KernelSpace

DeviceController


UserSpace

4. The OS schedules another process.

5. Meanwhile, the device controller reads from the device. Some other process is using the CPU

BLOCKED AnotherProcess

BLOCKED

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User Program

Operating System

DeviceDriver

KernelSpace

DeviceController


UserSpace

6. The read is complete. The device controller interrupts the CPU.

7. The interrupt handler determines which device caused the interrupt. It does its clean up and then sends a signal to the device driver to wake it up.

InterruptHandler

BLOCKED

BLOCKED

signal

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User Program

Operating System

DeviceDriver

KernelSpace

DeviceController


UserSpace

8. The device driver copies the data from the data registers in the device controller into the user’s address space. It then does a return to the application.

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processText to print

userspace

kernelspace

prin

t user process makesa print request

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Code executed when the system call is made

copy (userBuffer, kernelBuffer, count);enable interrupts; while (printerStatusReg != READY);printerDataReg = kernelBuffer[0];run scheduler;

Prints the first character

// Block the user and run some other process

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process

Text to print

userspace

kernelspace

blocked

The user process is blocked.

the print data is transferred

to the kernel.

process Another user process is scheduled to run.

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process

Text to print

userspace

kernelspace

blocked

the first character is sent to the printer

process while the printer works, this process can run.

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process

Text to print

userspace

kernelspace

blocked

The printer sends an interrupt.It is ready for another character.

process This process is interrupted.

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process

Text to print

userspace

kernelspace

blocked

the next character is sent to the printer

process while the printer works, this process can run again.

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process

userspace

kernelspace

When all of the data has beenprinted, the process is unblocked.

It will now be scheduled to run.

process

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Interrupt HandlersInterrupt HandlersInterrupt HandlersInterrupt Handlersoperatingsystems

Interrupt handlers are best hidden deep in the O/S. In the best case, drivers are kernel processes – they use privileged instructions.

have the driver starting an I/O operation block until an interrupt notifies it of completion

Interrupt procedure does its work - when finished it unblocks driver that started it

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Handling an InterruptHandling an InterruptHandling an InterruptHandling an Interruptoperatingsystems

Save any registers not saved by the interrupt hardware

Set up the context for the interrupt to run in Copy saved registers to the process table Set up stack for interrupt service procedure

Ack interrupt controller, re-enable interrupts

Run the interrupt handler

Determine which process to run next

Set up context for the next process to run

Load new process' registers

Start running the new process

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Print Driver Interrupt Service Routine

if (count == 0) done so unblock user;else{ i = i + 1; count = count -1; printerDataReg = kernelBuffer[i];}Acknowledge interrupt;Return from interrupt;

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operatingsystems

Device Manager DesignDevice Manager DesignDevice Manager DesignDevice Manager Design

User Program

Operating System

KernelSpace


UserSpace

read( device_x, … )

Trap Tableread( device_x )

read( deviceID, …){ switch(deviceID) { case dev0: dev0_read( … ); break;

case dev1: dev1_read( …); break; …

This designrequires that thekernel be recompiledevery time a newdevice is added.

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Reconfigurable DriversReconfigurable DriversReconfigurable DriversReconfigurable DriversDevice 01

Device 02

Device 03

Device 04

…

open( ) read( ) write( ) ioctl( )

When a new device is added, fill in entries in the table using a device “Registration” procedure.

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device management

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