P3L5 I/O Management

Question 1

When comparing I/O to a toy shop shipping dept., what is the example for “Have protocols”?

Answer 1

interfaces for device I/O

Question 2

When comparing I/O to a toy shop shipping dept., what is the example for “Have dedicated handlers”?

Answer 2

device drivers, interrupt handlers

Question 3

When comparing I/O to a toy shop shipping dept., what is the example for “Decouple I/O details for core processing”?

Answer 3

abstract I/O device detail from applications

Question 4

What are some examples of I/O devices?

Answer 4

Keyboard, microphone, speakers, display, mice, network interface cards…

Question 5

I/O Devices Quiz:
For each device, indicate whether it’s typically used for input (I), output (O) or both (B).

• keyboard
• speaker
• display
• hard disk drive
• microphone
• network interface cards (NIC)
• flash card

Answer 5

I - keyboard
O - speaker
O - display
B - hard disk drive
I - microphone
B - network interface cards (NIC)
B - flash card

Question 6

Name basic I/O Device features

Answer 6

• Control registers
• Micro controller
• On device memory
• Other logic

Question 7

What is the purpose of control registers in I/O?

Answer 7

control registers can be accessed by the CPU and permit the CPU/device interactions

Question 8

How are control registers divided? Explain each part.

Answer 8

• command registers, CPU uses to control what exactly the device will be doing
• data transfer registers, control the data that transfers in and out of the device
• status registers, used by the CPU to find out exactly what’s happening on the device

Question 9

Describe the microcontroller on an I/O device.

Answer 9

A microcontroller is like a device’s CPU. It is what controls all of the operations that actually take place on the device. It may be influenced by the CPU, but the microcontroller will make sure what things happen vs. not.

Question 10

What is PCI?

Answer 10

Peripheral Component Interconnect. It’s one of the standard methods for connecting devices to the CPU

Question 11

What do today’s platforms typically support in terms of PCI versions? Give some reasons why.

Answer 11

PCI Express Interconnect (PCIe)
which are technologically more advanced than PCI or PCI-X.
- More bandwidth
- faster
- has lower access latency
- supports more devices

Question 12

Name types of CPU - Device interconnects other than PCI bus

Answer 12

• SCSI bus
• peripheral bus
• bridges

Question 13

What determines what type of interconnect a device can directly attach to?

Answer 13

the controllers that are part of the device hardware

Question 14

What are bridge controllers?

Answer 14

They can handle differences between different types of interconnects

Question 15

T or F?

The operating system has to include a device driver for every type of different hardware device that is incorporated in the system.

Answer 15

True

Question 16

What are device drivers responsible for?

Answer 16

All aspects of device access, management and control.
This includes logic that determines
- how requests can be passed from the higher levels of the system software applications to the actual device,
- how the system can response to device-level events like errors, response notifications or status change info
- in general any device specific details regarding the device configuration or operation

Question 17

Who provides device drivers and are responsible for making sure they work for different OS or OS versions?

Answer 17

The manufacturers or the designers of the actual hardware

Question 18

How do OS’es typically standardize device driver interfaces?

Answer 18

they provide some device driver framework so that the device manufacturers can develop their drivers within that framework given the specific interfaces that the OS supports

Question 19

What are some benefits of standardizing device interfaces?

Answer 19

• device driver developers know exactly what is expected from the ways the rest of the OS will interact with their device
• The OS does not depend on one particular device (gives device independence and device diversity)

Question 20

Name some different types of devices

Answer 20

• Block: disk
• Character : keyboard
• Network devices

Question 21

What are key properties of Block: disk devices?

Answer 21

• read/write blocks of data

- direct access to arbitrary block

Question 22

What are properties of Character: keyboard devices?

Answer 22

• get/put character

Question 23

T/F

Network devices are somewhere in between block devices and character devices

Answer 23

True

Question 24

What is memory mapped I/O?

Answer 24

Part of ‘host’ physical memory is dedicated for device interactions

Question 25

What are Base Address Registers (BAR)?

Answer 25

These registers control the portion of the memory that’s reserved for device interactions (memory mapped I/O)

Question 26

What is the I/O port model?

Answer 26

A method for CPU to interact with devices that requires dedicated in/out instructions for device access

Question 27

What the two paths for devices to communicate to the CPU? Describe the pros and cons of each method.

Answer 27

Interrupt
 - interrupt handling steps
 \+ can be generated as soon as possible
Polling
 \+ when convenient for OS
 - delay or CPU overhead

Question 28

What is Programmed I/O (PIO)?

Answer 28

A method for the system to access/request an operation from a device.
There is no additional hardware support (involves CPU issuing instructions by writing into the command/data registers)
CPU “programs” the device
- via command registers
- data movement

Question 29

What is Direct Memory Access (DMA)?

Answer 29

Relies on DMA controller (special hardware)
CPU “programs” the device
- via command registers
- via DMA controls

Question 30

T/F

Memory can be swapped out to disk during a DMA transfer

Answer 30

F

Data buffer must be in physical memory until transfer completes