1. 5
Device Management

2. Input/Output Devices
Output Device
Processor
Input Device

3. The Device Driver Interface…
write(…);
Device Interface
Terminal
Driver
Printer
Driver
Disk
Driver
Terminal
Controller
Printer
Controller
Disk
Controller

4. Device Management Organization
Application
Process
System Interface
File
Manager
Device-Independent
Device-Dependent
Hardware Interface
Command
Status
Data
Device Controller

5. 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)

6. 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

7. 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)
Data on device
Variable x
Register
Device dev_I
Memory
CPU

8. Gantt Chart
A Gantt chart is a graphical representation of the duration of tasks against the progression of time.

9. Gantt Chart
Gantt charts are useful tools for planning and scheduling projects.
Gantt charts allow you to assess how long a project should take.
Gantt charts lay out the order in which tasks need to be carried out.
Gantt charts help manage the dependencies between tasks.
Gantt charts determine the resources needed.

10. Gantt Chart Gantt charts are useful tools when a project is under way.
Gantt charts monitor progress.
You can immediately see what should have been achieved at a point in time.
Gantt charts allow you to see how remedial action may bring the project back on course.

11. Henry Laurence Gantt ( ) was a mechanical engineer, management consultant and industry advisor.
Henry Laurence Gantt developed Gantt charts in the second decade of the 20th century.
Gantt charts were used as a visual tool to show scheduled and actual progress of projects.
Accepted as a commonplace project management tool today, it was an innovation of world-wide importance in the 1920s. 
Gantt charts were used on large construction projects like the Hoover Dam started in 1931 and the interstate highway network started in 1956.

12. Henry Gantts contribution to the management process is honored today through the Henry Laurence Gantt Medal. 
The award established in 1929 is given for distinguished achievement in management and for service to the community.

13. Overlapping CPU-Controller Operations in a Process
I/O Ctlr t1 t2 t3 t4 t5 t6 t7 t8 t9

14. Overlapping Processing and I/O
I/O Ctlr t1 t2 t3 t4

15. I/O strategies 1. Direct I/O with Polling. 2. DMA I/O with Polling.
3. Direct I/O with Interrupt.
4. DMA I/O with Interrupt.

16. Polling I/O Read Operation
read(device, …); 1
Data
System Interface
read function 5
write function 2 3 4
Hardware Interface
Command
Status
Data
Device Controller

17. Direct I/O with Polling (IN)
1. The application process requires a read operation.
2. The device driver queries the status register to determine if the device is idle, if the device is busy, the driver waits for it to be idle.
3. The driver stores an input command into the controller’s command register, thereby, starting the device.
4. The driver repeatedly reads the status register while waiting for the device to complete its operation.
5. The driver copies the contents of the controller’s data register(s) into process’s space.

18. Direct I/O with Polling (OUT)
1. Process requests an output operation.
2. Driver status register, busy? Wait.
3. Driver copies data from user space memory controller’s data registers.
4. The driver stores an output command into the command register, thereby starting the device.
5. The driver repeatedly reads the status register while waiting for the device to complete the operation.

19. Interrupt-driven I/O Operation
read(device, …); 9 1 8b
Data
System Interface
Device Status Table 4 7
Device
Handler
read driver 2
write driver 6 3 8a
Interrupt
Handler
Hardware Interface 5
Command
Status
Data
Device Controller

20. Interrupt Driven I/O Operation
1. Process requests a read operation
2. Top half of the driver queries the status register, idle? -> Yes! -> Wait!
3. If no longer busy, the driver stores command into the controller’s command register and thereby starting the device for read operation.
4. When read driver completes its work, information regarding the op -> device status table.

21. Device Status Table contains an entry for each device in the system.
5. Eventually, the driver completes the operation and interrupt the CPU and cause the interrupt handler to run.
6. The interrupt handler determines which device caused the interrupt. It then branches to the device handler for that device.
7. The device handler retrieves the pending I/O status information from the device status table.
8. The device handler copies the contents of the controller’s data registers into the user process’s space (memory).
9. The device handler-behaving as the bottom half of the device driver invoked by the application process-thus returns control to the application process.

22. Device Independent Function Call
Trap Table
funci(…)
dev_func_i(devID, …) {
// Processing common to all devices …
switch(devID) {
case dev0: dev0_func_i(…);
break;
case dev1: dev1_func_i(…);
case devM: devM_func_i(…); }; }

23. 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)

24. Reconfigurable Device Drivers
System call interface
open(){…}
read(){…}
Entry Points for Device j
etc.
Other
Kernel
services
Driver for Device j

25. Handling Interrupts Device driver J Device interrupt handler J
Device status table
int read(…) {
// Prepare for I/O
save_state(J);
out dev#
// Done (no return) }
void dev_handler(…) {
get_state(J);
//Cleanup after op
signal(dev[j]);
return_from_sys_call(); } J
Interrupt Handler
Device Controller

26. Handling Interrupts(2)
Device driver J
Device interrupt handler J
int read(…) { …
out dev#
// Return after interrupt
wait(dev[J});
return_from_sys_call(); }
void dev_handler(…) {
//Cleanup after op
signal(dev[j]); }
Interrupt Handler
Device Controller

27. The Pure Cycle Water Company
Customer Office
Water Company
Returning the Empties
Water Producer
Water Consumers
Delivering Water

28. Hardware Buffering Process reads bi-1 Controller reads bi
Data A B A B
Device
Device
Device
Process reads bi-1
Controller reads bi
Process reads bi
Controller reads bi+1
Unbuffered

29. Double Buffering in the Driver
Process
Process A B A B
Driver
Controller
Controller A B A B
Hardware
Device
Device

30. Circular Buffering
To data consumer
Buffer i
Buffer j
From data producer

31. A Generic Communications Device
Bus
Generic
Controller
Communications
Controller
Local
Device
Cabling connecting the
controller to the device
Device
Printer
Modem
Network

32. Rotating Media Cylinder (set of tracks) Track (Cylinder) Sector
(a) Multi-surface Disk
(b) Disk Surface
(b) Cylinders

33. Storage Device Driver SCSI API Controller (SCSI) Magnetic Disk
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

34. Compute vs I/O Bound
Compute-bound
Time
I/O-bound

35. 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

36. Optimizing Seek Time
Multiprogramming on I/O-bound programs => set of processes waiting for disk
Seek time dominates access time => minimize seek time across the set
Tracks 0:99; Head at track 75, requests for 23, 87, 36, 93, 66
FCFS: = 251 steps

37. Optimizing Seek Time (cont)
Requests = 23, 87, 36, 93, 66
SSTF: (75), 66, 87, 93, 36, 23
= 107 steps
Scan: (75), 87, 93, 99, 66, 36, 23
= 100 steps
Look: (75), 87, 93, 66, 36, 23
= 87 steps

38. Optimizing Seek Time (cont)
Requests = 23, 87, 36, 93, 66
Circular Scan: (75), 87, 93, 99, 23, 36, 66
home = 90 + home
Circular Look: (75), 87, 93, 23, 36, 66
home = 84 + home

39. Serial Port
CPU
Memory
Serial
Device
Printer
Terminal
Modem
Mouse
etc.

40. UART
universal
asynchronous
receiver-
transmitter

42. Serial Port Device Driver Software on the CPU Bus Interface UART API
Device Driver API
Device Driver
Set UART parms
read/write ops
Interrupt hander
Software on the CPU
Bus Interface
UART API
parity
bits per byte
etc.
Serial Device
(UART)
RS-232 Interface
9-pin connector
4-wires
bit transmit/receive
...

43. Switched Telephone Network
Adding a Modem
CPU
Dialing & connecting
Convert analog voice to/from digital
Convert bytes to/from bit streams
Transmit/receive protocol
Memory
Serial
Device
Modem
Phone
Switched Telephone Network

44. Serial Communication Device Driver Serial Device RS-232 Modem
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

45. Exploiting the Phone Network
Logical Communication
CPU
CPU
Memory
Comm
Device
Comm
Device
Memory
Modem
Modem
Phone
Phone
Switched Telephone Network

46. Logical Communication
Data Networks
Technology focus includes protocols and software
(more on this later … Chapter 15 and beyond ...)
Logical Communication
CPU
CPU
Memory
Network
Device
Network
Device
Memory
Data Network

47. The USB Process
When the host powers up, it queries all of the devices connected to the bus and assigns each one an address.
This process is called enumeration -- devices are also enumerated when they connect to the bus.
The host also finds out from each device what type of data transfer it wishes to perform:

48. Interrupt - A device like a mouse or a keyboard, which will be sending very little data, would choose the interrupt mode.
Bulk - A device like a printer, which receives data in one big packet, uses the bulk transfer mode. A block of data is sent to the printer (in 64-byte chunks) and verified to make sure it is correct.
Isochronous - A streaming device (such as speakers) uses the isochronous mode. Data streams between the device and the host in real-time, and there is no error correction.

49. MS Disk Description-Boot Sector

50. NT Driver Organization

51. 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