Device Management

1
Device Management
2
Serial Port
CPU
Serial Device
Memory

• Printer
• Terminal
• Modem
• Mouse
• etc.

3
Serial Port
Device Driver API

• Device Driver
• Set UART parms
• read/write ops
• Interrupt hander

Software on the CPU
Bus Interface
Serial Device (UART)

• UART API
• parity
• bits per byte
• etc.

• RS-232 Interface
• 9-pin connector
• 4-wires
• bit transmit/receive
• ...

4
Adding a Modem
CPU

• Dialing connecting
• Convert analog voice to/from digital
• Convert bytes to/from bit streams
• Transmit/receive protocol

Serial Device
Memory
Modem
Phone
Switched Telephone Network
5
Serial Communication

• Device Driver
• Set UART parms
• read/write ops
• Interrupt hander

• Driver-Modem Protocol
• Dialing connecting
• Convert analog voice to/from digital
• Convert bytes to/from bit streams
• Transmit/receive protocol

Serial Device
RS-232
Modem
6
Exploiting the Phone Network
Logical Communication
CPU
CPU
Comm Device
Memory
Comm Device
Memory
Modem
Modem
Phone
Phone
Switched Telephone Network
7
Data Networks

• Technology focus includes protocols and software
• (more on this later Chapter 15 and beyond
  ...)

Logical Communication
CPU
CPU
Network Device
Memory
Network Device
Memory
Data Network
8
Rotating Storage
Track (Cylinder)
Sector
Top View of a Surface
9
MS Disk Description
10
Storage Device
Device Driver API

• Driver
• Get disk description
• Set SCSI parms
• read/write ops
• Interrupt hander

• SCSI API
• commands
• bits per byte
• etc.

Controller
(SCSI)
Magnetic Disk
11
Device Management Organization
Application Process
System Interface
File Manager
Device Driver
Hardware Interface
Command
Status
Data
Device Controller
12
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 access
• Device driver implements functions (one entry
  point per API function)

13
Example BSD UNIX Driver
open Prepare dev for operation close No longer
using the device ioctl Character dev specific
info read Character dev input op write Character
dev output op strategy Block dev input/output
ops select Character dev check for
data stop Discontinue a stream output op
14
Read with Polling
read(device, )
Data
1
System Interface
read function
5
write function
2
3
4
Hardware Interface
Command
Status
Data
Device Controller
15
Read Using Interrupts
read(device, )
9
1
8b
Data
System Interface
Device Status Table
4
7
Device Handler
read driver
write driver
2
6
3
8a
Interrupt Handler
5
Hardware Interface
Command
Status
Data
Device Controller
16
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)

17
Reconfigurable Drivers
System call interface
open()
read()
Entry Points for Device j
etc.
Other Kernel services
Driver for Device j
18
NT Driver Organization
19
NT Device Drivers

• API model is the same as for a file
• Extend device management by adding modules to the
  stream
• Device driver is invoked via an Interrupt Request
  Packet (IRP)
• IRP can come from another stream module
• IRP can come from the OS
• Driver must respond to minimum set of IRPs
• See Part I of notes

20
Memory Mapped I/O
Primary Memory
Primary Memory
Memory Addresses
Device 0
Device 0
Memory Addresses
Device 1
Device 1
Device Addresses
Device n-1
Device n-1
21
CPU-I/O Overlap
. . . startRead(dev_I, d, x) . .
. While(stillReading()) y f(x) . . .
. . . read(dev_I, d, x) y f(x) . . .
Data on device
Variable x
Register
Device dev_I
Memory
CPU
22
I/O - CPU Overlap
App 1
App 2
I/O Ctlr
t1
t2
t3
t4
Overlapping App 1s I/O with App 2
App
I/O Ctlr
t1
t2
t3
t4
t5
t6
t7
t8
t9
Overlapping App CPU with its own I/O
23
Direct Memory Access
Primary Memory
Primary Memory
CPU
CPU
Controller
Controller
Device
Device
24
Buffering
Water Company
Customer Office
Returning the Empties
Water Producer
Water Consumers
Delivering Water

• Water bottles are buffers
• Office workers consume water from a buffer while
• water company fills other buffers

25
Hardware Buffering
Process
Process
Controller
Controller
Data
B
A
Device
Device
Process reads bi-1 Controller reads bi
Unbuffered
26
Hardware Buffering
Process
Process
Process
Controller
Controller
Controller
Data
B
A
B
A
Device
Device
Device
Process reads bi-1 Controller reads bi
Process reads bi Controller reads bi1
Unbuffered
27
Buffering in the Driver
Process
B
A
Driver
Controller
B
A
Hardware
Device
28
Buffering in the Driver
Process
Process
B
A
B
A
Driver
Controller
Controller
B
A
B
A
Hardware
Device
Device
29
A Ring Buffer
To data consumer
Buffer i
Buffer j
From data producer
30
Compute vs I/O Bound
Compute-bound
Time
I/O-bound
31
Disk Optimizations

• Transfer Time Time to copy bits from disk
  surface to memory
• Disk latency time Rotational delay waiting for
  proper sector to rotate under R/W head
• Disk seek time Delay while R/W head moves to the
  destination track/cylinder
• Access Time seek latency transfer

32
Optimizing Seek Time

• Multiprogramming on I/O-bound programs gt set of
  processes waiting for disk
• Seek time dominates access time gt minimize seek
  time across the set
• Tracks 099 Head at track 75, requests for 23,
  87, 36, 93, 66
• FCFS 52 64 51 57 27 251 steps

33
Optimizing Seek Time (cont)

• Requests 23, 87, 36, 93, 66
• SSTF (75), 66, 87, 93, 36, 23
• 11 21 6 57 13 107 steps
• Scan (75), 87, 93, 99, 66, 36, 23
• 12 6 6 33 30 13 100 steps
• Look (75), 87, 93, 66, 36, 23
• 12 6 27 30 13 87 steps

34
Optimizing Seek Time (cont)

• Requests 23, 87, 36, 93, 66
• Circular Scan (75), 87, 93, 99, 23, 36, 66
• 12 6 6 home 23 13 30 90 home
• Circular Look (75), 87, 93, 23, 36, 66
• 12 6 home 23 13 30 84 home