Basics Of Device Driver Types

Question 1

The directory on a Linux machine where all the device files for the system are located.

Answer 1

/dev

Question 2

/dev is a very interesting directory that highlights one important aspect of the Linux filesystem

Answer 2

Everything in Linux is a file

Question 3

An example of the Printer driver in your Linux System. The device file of printer is /dev/lp0.

Answer 3

Any data written to this file by your application will be re-directed to your computer.

Question 4

Data read/written to /dev/ttys0 will

Answer 4

allow you to communicate with a device like a serial terminal or a modem device.

Question 5

In Linux we have following device types:

Answer 5

1. Character Devices
2. Block Devices
3. Network Devices

Question 6

Character Devices Driver

Answer 6

A character device typically transfers data to and from a user application- they behave like pipes or serial ports, instantly reading or writing the byte data in a character-by-character stream.

Question 7

Character Device Drivers Framework

Answer 7

They provide the framework for many typical drivers, such as those that are required for interfacing to serial communications, video capture, and audio devices.

Question 8

Block Device

Answer 8

Block devices behave in a similar fashion to regular files, allowing a buffered array of cached data to be viewed or manipulated with operations such as reads, writes, and seeks.

Question 9

LKM

Answer 9

Linux Kernal Space

Question 10

Major and Minor Numbers

Answer 10

Device drives have an associated major and minor number. For example /dev/ram0 and /dev/null are associated with a drive with a major number 1, and /dev/tty0 and /dev/ttys0 are associated with a driver with major number 4. The Major number is used by the kernel to identify the correct device driver when the device is accessed. The role of the minor number is device dependent and is handled internally within the driver.

molloyd@beaglebone:/dev$ ls -l
crw-rw—T 1 root i2c 89, 0 Jan 1 2000 i2c-0
brw-rw—T 1 root disk 1, 0 Mar 1 20:46 ram0
brw-rw—T 1 root floppy 179, 0 Mar 1 20:46 mmcblk0
crw-rw-rw- 1 root root 1, 3 Mar 1 20:46 null
crw——- 1 root root 4, 0 Mar 1 20:46 tty0
crw-rw—T 1 root dialout 4, 64 Mar 1 20:46 ttyS0

Question 11

molloyd@beaglebone:/dev$ ls -l
crw-rw—T 1 root i2c 89, 0 Jan 1 2000 i2c-0
brw-rw—T 1 root disk 1, 0 Mar 1 20:46 ram0
brw-rw—T 1 root floppy 179, 0 Mar 1 20:46 mmcblk0
crw-rw-rw- 1 root root 1, 3 Mar 1 20:46 null
crw——- 1 root root 4, 0 Mar 1 20:46 tty0
crw-rw—T 1 root dialout 4, 64 Mar 1 20:46 ttyS0

Answer 11

Character devices are identified by a ‘c’ in the first column of a listing, and block devices are identified by a ‘b’. The access permissions, owner, and the group of the device is provided for each device.

Question 12

Examples of character device drivers are

Answer 12

• Serial port ( /dev/ttyS0 )
• Text console ( /dev/console )
• Mice
• Parallel printer ports

Question 13

Examples of Block device

Answer 13

• Hard Drive

- Cd-Rom

Question 14

In what way do Block and Character devices differ?

Answer 14

Block and Character devices differ only in the way the data is managed internally by the kernal.

Question 15

Block devices in short are

Answer 15

Block devices in short are devices that store or hold data.

Question 16

Network device

Answer 16

Network devices receive and transmit data packets on hardware interface that connect to external systems and provide a uniform interface that network protocols can access.

Question 17

Network device vs. Block device

Answer 17

Block drivers operate only in response to requests from the kernal, whereas network drivers receive packets asynchronously from outside. Thus, while a block driver is asked to send a buffer toward the kernal, the network device asks to push incomming packets tooward the kerrnal. The kernal interface for network drivers is designed for this different mode of operation.