1 input/output the messiest part of o.s. chap11. 2 speed difference of i/o hardware

1

Input/OutputThe messiest part of O.S.

Chap11

2

Speed difference of I/O Hardware

3

Device Controllers

• I/O devices have components:– mechanical component – electronic component

• The electronic component is the device controller– may be able to handle multiple devices

• Controller's tasks– convert serial bit stream to block of bytes– perform error correction as necessary– make available to main memory

4

Memory-Mapped I/O (1)

• Separate I/O and memory space• Memory-mapped I/O• Hybrid

5

Memory-Mapped I/O (2)

(a) A single-bus architecture(b) A dual-bus memory architecture

6

I/O Architecture

• Several types of bus,such as ISA, EISA,PCI and MCA, are currently in use.

• data bus – the pentium has 64 bit wide data bus• Address bus – • Control bus – a group of lines that transmit control

information to the connected circuits. The Pentium uses control lines to specify, for example, whether the bus is used to allow data transfers between a processor and the RAM, or alternatively, between a processor and an I/O device.

7

CPUCPU

I/O busI/O bus

I/O PortI/O Port I/O PortI/O Port

I/O InterfaceI/O Interface

I/O ControllerI/O Controller

PC’s I/O architecturePC’s I/O architecture

8

PC’s I/O architecture

• When a bus connects to the CPU to an I/O device, it is called an I/O bus.

• 80x86 use 16 out of the 32 address lines to address I/O devices and 8,16, or 32 out of the 64 data lines to transfer data

9

I/O ports

• Each device connected to the I/O bus has its own I/O address, which are usually called I/O ports

• PC provides up to 65536 8-bits I/O ports. Two consecutive 8-bit ports may be regarded as a single 16-bit port.

• Four assembly instructions in,ins,out,outs allow CPU to read and write into an I/O port

10

Memory mapped I/O ports in PC

• PC’s device I/O ports may also be mapped into address of physical address space.

• O.S. can use mov instruction that operate directly on memory.

• Modern hardware devices are more suited to mapped I/O, since it is faster and can be combined with DMA

11

I/O and registers

• The I/O ports of each device are actually structured into a set of specialized registers

• CPU write commands to control registers• CPU reads a value that represents the internal

state of the device from status register• CPU fetch data from a device by reading input

register• CPU push data to device by writing bytes into

output registers

12

CPUCPU

Control registerControl register

Status registerStatus register

input registerinput register

Output registerOutput register

Device’sDevice’sI/O InterfaceI/O Interface

Specialized I/O ports

13

• To lower costs, the same I/O port is often used for different purposes. e.g., some bits describe the device state and others are used to specifycommands.e.g., the same I/O ports may be used as an input register or an output register

14

What is an I/O interface?

• An I/O interface is a hardware circuit inserted between a group of I/O ports and the corresponding device controller.

• It acts as an interpreter that translates the values in the I/O ports into commands and data for the device.

15

Types of I/O interfaces

• Custom I/O interfaces– devoted to one specific hardware device– usually, the device controller is on the

same card of I/O interfaces.

• General-purpose I/O interface– used to connect several different

hardware devices

16

Custom I/O interfaces

• Keyboard interface• Graphic interface • Disk interface• Network interface

17

General –purpose I/O interface

• Parallel port– traditionally connected to printers, but can also be

connected to removable disks, scanners

• Serial port– one bit at a time– use UART chip (Universal Asynchronous Receiver and

Transmitter) to string out the bytes into a sequence of bits.

• Universal serial bus (USB)• PCMCIA interface• SCSI (Small Computer System Interface) Interface

18

Device Controller

• It interprets the high-level commands received from the I/O interface and force the device to execute specific actions by sending proper sequence of electrical signals

• It converts and properly interprets the electrical signals received from the device and modifies (through the I/O interface) the value of the status register

19

I/O shared memory

• Several hardware device sometimes include their own memory, which is often called I/O shared memory. E.g. graphic cards.

20

PC’s mapping addressesof I/O shared memory

• For device connected to ISA bus– mapped into physical address from

0xa0000 to 0xfffff: a hole between 640K-1MB. These are reserved page frames

• For some old devices using VESA Local bus– 0xe00000 to 0xffffff : 14MB-16MB– going out of production

• For device connected to PCI bus– is mapped into very large physical address, well above the end

of RAM’s physical address. Much simpler to handle• AGP (Accelerated Graphics Port)

– use a special hardware circuit GART (Graphics Address Remapping Table)

– GART enables AGP to sustain much higher data transfer rate.

21

Direct Memory Access (DMA)

Operation of a DMA transfer

22

Interrupts Revisited

How interrupts happens. Connections between devices and interrupt controller actually use interrupt lines on the bus rather than dedicated wires

23

Principles of I/O SoftwareGoals of I/O Software (1)

• Device independence– programs can access any I/O device – without specifying device in advance

· (floppy, hard drive, or CD-ROM)

• Uniform naming– name of a file or device a string or an

integer– not depending on which machine

• Error handling– handle as close to the hardware as possible

24

Goals of I/O Software (2)

• Synchronous vs. asynchronous transfers– blocked transfers vs. interrupt-driven

• Buffering– data coming off a device cannot be stored

in final destination

• Sharable vs. dedicated devices– disks are sharable– tape drives would not be

25

Programmed I/O (1)

Steps in printing a string

26

Programmed I/O (2)

Writing a string to the printer using programmed I/O

27

Interrupt-Driven I/O

• Writing a string to the printer using interrupt-driven I/O– Code executed when print system call is made– Interrupt service procedure

28

I/O Using DMA

• Printing a string using DMA– code executed when the print system call is made– interrupt service procedure

29

I/O Software Layers

Layers of the I/O Software System

30

Interrupt Handlers (1)

• Interrupt handlers are best hidden– have driver starting an I/O operation block until

interrupt notifies of completion

• Interrupt procedure does its task– then unblocks driver that started it

• Steps must be performed in software after interrupt completed

1. Save regs not already saved by interrupt hardware

2. Set up context for interrupt service procedure

31

Interrupt Handlers (2)

3. Set up stack for interrupt service procedure4. Ack interrupt controller, reenable interrupts5. Copy registers from where saved6. Run service procedure 7. Set up MMU context for process to run next8. Load new process' registers9. Start running the new process

32

Device Drivers

• Logical position of device drivers is shown here• Communications between drivers and device controllers goes

over the bus

33

Device-Independent I/O Software (1)

Functions of the device-independent I/O software

Uniform interfacing for device drivers

Buffering

Error reporting

Allocating and releasing dedicate devices

Providing a device-independent block size

34

Device-Independent I/O Software (2)

(a) Without a standard driver interface(b) With a standard driver interface

35

Device-Independent I/O Software (3)

(a) Unbuffered input(b) Buffering in user space(c) Buffering in the kernel followed by copying to user

space(d) Double buffering in the kernel

36

Device-Independent I/O Software (4)

Networking may involve many copies

37

User-Space I/O Software

Layers of the I/O system and the main functions of each layer

38

UNIX I/O (1)/Device Driver

Some of the fields of a typical cdevsw table

39

UNIX I/O (2)

The UNIX I/O system in BSD

40

Streams

An example of streams in System V

41

Disk Hardware (1)

Disk parameters for the original IBM PC floppy disk and a Western Digital WD 18300 hard disk

42

Disk Hardware (2)

• Physical geometry of a disk with two zones• A possible virtual geometry for this disk

43

Disk Hardware (3)

• Raid levels 0 through 2 • Backup and parity drives are shaded

44

Disk Hardware (4)

• Raid levels 3 through 5• Backup and parity drives are shaded

45

Disk Hardware (5)

Recording structure of a CD or CD-ROM

46

Disk Hardware (6)

Logical data layout on a CD-ROM

47

Disk Hardware (7)

• Cross section of a CD-R disk and laser– not to scale

• Silver CD-ROM has similar structure– without dye layer– with pitted aluminum layer instead of gold

48

Disk Hardware (8)

A double sided, dual layer DVD disk

49

Disk Formatting (1)

A disk sector

50

Disk Formatting (2)

An illustration of cylinder skew

51

Disk Formatting (3)

• No interleaving• Single interleaving• Double interleaving

52

Disk Arm Scheduling Algorithms (1)

• Time required to read or write a disk block determined by 3 factors

1. Seek time2. Rotational delay3. Actual transfer time

• Seek time dominates• Error checking is done by controllers

53

Disk Arm Scheduling Algorithms (2)

Shortest Seek First (SSF) disk scheduling algorithm

Initialposition

Pendingrequests

54

Disk Arm Scheduling Algorithms (3)

The elevator algorithm for scheduling disk requests

55

Error Handling

• A disk track with a bad sector• Substituting a spare for the bad sector• Shifting all the sectors to bypass the bad

one

56

Stable Storage

Analysis of the influence of crashes on stable writes

57

ClocksClock Hardware

A programmable clock

58

Clock Software (1)

Three ways to maintain the time of day

59

Clock Software (2)

Simulating multiple timers with a single clock

60

Soft Timers

• A second clock available for timer interrupts– specified by applications– no problems if interrupt frequency is low

• Soft timers avoid interrupts– kernel checks for soft timer expiration before

it exits to user mode– how well this works depends on rate of

kernel entries

61

Character Oriented TerminalsRS-232 Terminal Hardware

• An RS-232 terminal communicates with computer 1 bit at a time• Called a serial line – bits go out in series, 1 bit at a time• Windows uses COM1 and COM2 ports, first to serial lines• Computer and terminal are completely independent

62

• Central buffer pool• Dedicated buffer for each terminal

Input Software (1)

63

Input Software (2)

Characters handled specially in canonical mode

64

Output Software

The ANSI escape sequences• accepted by terminal driver on output• ESC is ASCII character (0x1B)• n,m, and s are optional numeric parameters

65

Display Hardware (1)

Memory-mapped displays• driver writes directly into display's video RAM

Parallel port

66

Display Hardware (2)

• A video RAM image – simple monochrome display– character mode

• Corresponding screen– the xs are attribute bytes

67

Input Software

• Keyboard driver delivers a number– driver converts to characters– uses a ASCII table

• Exceptions, adaptations needed for other languages– many OS provide for loadable keymaps or

code pages

68

Output Software for Windows (1)

Sample window located at (200,100) on XGA display

69

Output Software for Windows (2)

Skeleton of a Windows main program (part 1)

70

Output Software for Windows (3)

Skeleton of a Windows main program (part 2)

71

Output Software for Windows (4)

An example rectangle drawn using Rectangle

72

Output Software for Windows (5)

• Copying bitmaps using BitBlt.– before– after

73

Output Software for Windows (6)

Examples of character outlines at different point sizes

74

Network TerminalsX Windows (1)

Clients and servers in the M.I.T. X Window System

75

X Windows (2)

Skeleton of an X Windows application program

76

The SLIM Network Terminal (1)

The architecture of the SLIM terminal system

77

The SLIM Network Terminal (2)

Messages used in the SLIM protocol from the server to the terminals

78

Power Management (1)

Power consumption of various parts of a laptop computer

79

Power management (2)

The use of zones for backlighting the display

80

Power Management (3)

• Running at full clock speed

• Cutting voltage by two – cuts clock speed by two, – cuts power by four

81

Power Management (4)

• Telling the programs to use less energy– may mean poorer user experience

• Examples– change from color output to black and

white– speech recognition reduces vocabulary– less resolution or detail in an image