1. Input/Output The messiest part of O.S.
Chap11
Input/Output The messiest part of O.S.

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. PC’s I/O architecture CPU I/O bus I/O Port I/O Port I/O Interface
I/O Controller

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 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. Specialized I/O ports Control register Device’s Status register CPU
I/O Interface
CPU
Status register
input register
Output register

13. To lower costs, the same I/O port is often used for different purposes
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 specify commands. 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 addresses of 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 Software Goals 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. Steps in printing a string
Programmed I/O (1)
Steps in printing a string

26. 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. Layers of the I/O Software System
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
Save regs not already saved by interrupt hardware
Set up context for interrupt service procedure

31. Interrupt Handlers (2) Set up stack for interrupt service procedure
Ack interrupt controller, reenable interrupts
Copy registers from where saved
Run service procedure
Set up MMU context for process to run next
Load new process' registers
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)
Uniform interfacing for device drivers
Buffering
Error reporting
Allocating and releasing dedicate devices
Providing a device-independent block size
Functions of the device-independent I/O software

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. The UNIX I/O system in BSD

40. 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 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. Logical data layout on a CD-ROM
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. A double sided, dual layer DVD disk
Disk Hardware (8)
A double sided, dual layer DVD disk

49. Disk Formatting (1)
A disk sector

50. An illustration of cylinder skew
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
Seek time
Rotational delay
Actual transfer time
Seek time dominates
Error checking is done by controllers

53. Disk Arm Scheduling Algorithms (2)
Initial
position
Pending
requests
Shortest Seek First (SSF) disk scheduling algorithm

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. Analysis of the influence of crashes on stable writes
Stable Storage
Analysis of the influence of crashes on stable writes

57. Clocks Clock Hardware
A programmable clock

58. Three ways to maintain the time of day
Clock Software (1)
Three ways to maintain the time of day

59. Simulating multiple timers with a single clock
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 Terminals RS-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. Input Software (1) Central buffer pool
Dedicated buffer for each terminal

63. Characters handled specially in canonical mode
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
Parallel port
Memory-mapped displays
driver writes directly into display's video RAM

66. Display Hardware (2) A video RAM image Corresponding screen
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 Terminals X Windows (1)
Clients and servers in the M.I.T. X Window System

75. 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 consumption of various parts of a laptop computer
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 Examples
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