This document discusses device drivers. It begins by defining a device driver as software that allows operating systems and applications to access hardware functionality. It then describes the main objectives of device drivers and how they handle requests from the operating system. Next, it covers different types of device drivers and provides examples. Applications of device drivers for storage, input/output, virtual machines, and peripherals are also outlined. Finally, the document lists the typical steps taken when developing new device drivers.

1. GROUP 20
Operating Systems
NAMES STUDENT_NUMBER REG_NUMBER
NSEREKO KAYONGO JULIUS 2100714339 21/U/14339/PS
MUTUMBA ROBERT 2100711810 21/U/11810/EVE
AMANDA ANN KIRABO 2100704763 21/U/04763/PS
ALIDDEKI MULINDWA BRYAN 2100700663 21/U/0663
NANYONGA RAHMAH 2100711530 21/U/11530/PS

2. DEVICE DRIVERS
 A device driver is a specialized software that
operates a particular computer-connected device
offering a software interface to the hardware allows
operating systems and other computer applications
to access hardware functionalities.
 The hardware is linked to a computer
bus/communication subsystem via which device
drivers interact with the device. They are
hardware-dependent and operating-system-
specific (OS). They offer the interrupt processing
essential for any time-dependent asynchronous
hardware interface.

3.  A device driver’s primary objective is to allow computers
and network hardware components to interface and
interact with specific devices. They handle requests made
by the kernel concerning a particular type of device.
 Device drivers define messages and mechanisms through
which the computer’s operating system and applications
can access the device or make requests for the device.
They also handle device responses and messages for
delivery to the computer.
Device Drivers cont’d

4. Device Drivers cont’d

5. How do device drivers handle requests
 Device drivers receive requests for device
access and actions from the Operating
System and it’s active applications to their
respective hardware devices.
 Suppose a request comes to read block N. If
a driver is idle when the request arrives, it
starts carrying out the request immediately. If
the driver is already busy with some other
request, it places a new request in the queue
of the pending request.

6. Illustration
 Block N is called the block device and this devices
communicate with the driver by sending the entire blocks
of data. For example, hard disks.

7. TYPES OF DEVICE DRIVERS
1. Kernel device drivers
Kernel device drivers consist of some generic hardware loaded
with the operating system (OS) as part of the OS. They include
motherboards, processors, and BIOS. They are invoked and
loaded into the random-access memory (RAM) when required.
2. User-mode device drivers
User mode device drivers refer to device drivers that users may
trigger during a session. When using a system, users may have
their own external devices that they bring to use, such as
external plug-and-play devices. These devices also require
drivers to function. Users can write these drivers to the disk to
reduce strain on computer resources.

8. 3. Character drivers
Character device drivers provide unstructured access to the
hardware. They transfer data to and from devices without using a
specific device address. They allow the reading or writing of one
byte at a time as a stream of sequential data.
4. Block drivers
Block device drivers provide structured access to the hardware.
They use file system block-sized buffers from a buffer cache
supplied by the kernel to perform I/O. A buffer cache is a memory
pool established by the kernel to store frequently accessed blocks
via block devices. The buffer cache reduces the amount of I/O
queries that need an I/O operation from the device.

9. 5. Original equipment manufacturer (OEM) drivers
Device drivers can be categorized as generic or OEM-related.
Generic drivers refer to device drivers with their operating
software bundled into the OEM hardware. One can use
generic drivers with different brands of a particular device type.
For instance, Linux works with several generic drivers that
function without the need to install any other software
manually.
6. Virtual device drivers
Virtual device drivers operate in both virtualization and non-
virtualization environments. In virtualization environments,
these drivers are used to emulate the hardware of the host
device. They control or manage the resource hardware of the
host device to ensure that both the guest and host device run
as expected.

10. 7. BIOS
The basic input output system (BIOS) is located in a ROM chip,
which ensures that BIOS will be available even when the hard
disk is formatted. It performs power-on self-tests (POST) that
are required during startup. The BIOS also provides drivers for
the basic hardware, such as keyboards and monitors, to ensure
that they interface with the operating system to function as
intended.
8. Motherboard drivers
Motherboard drivers exist within the operating system and
enable fundamental computer operations. These drivers
comprise applications that allow the keyboard and mouse’s
USB devices and I/O ports to work. Some motherboards have
drivers that support video and audio.

11. 9. Open-source drivers
Open-source drivers refer to drivers that are released under a free
and open-source license. For instance, open-source graphic
drivers control the output to the display if the display is part of the
graphics hardware.
The source code for open-source drivers is available to everyone,
making software collaborations easier. They are more trustworthy
as people can check them for any malicious code.

12. Applications of Device Drivers
Accessing Storage Systems
 Computer storage systems allow users to store data and
make it available on demand. They include external and
internal devices such as USB flash drives, hard drives,
and network-attached storage. Drivers in storage
systems enable them to interact with the computer. This
ensures that the computer can access its internal or
external storage systems, query their information, and
allow data transfer

13. Applications of Device Drivers (ctd)
For Input and Output Devices
 The computer’s OS interacts with device drivers to
ensure its hardware functions as expected. Input devices
include mice and keyboards, while output devices
include display devices such as monitors. Keyboards,
mice, and monitors are categorized as plug-and-play
devices

14. Applications of Device Drivers (ctd)
Control and management of virtual machines
When a guest operating system works on a host, it makes function calls to virtual device
drivers to access the hardware. In addition, they imitate processor-level occurrences like
interrupts and transmit them to the virtual machine.

15. Applications of Device Drivers (ctd)
BIOS for booting and hardware support
The BIOS performs the POST to ensure that all devices
are correctly configured before the computer can resume
with the normal booting process. This is an essential part
of botting

16. Applications of Device Drivers (ctd)
Smooth functioning of peripherals (e.g., printers, keyboards)
The device drivers responsible for PnP (Plug and Play)
have eased attachment of computer peripherals onto the
computer ports.
This ensures that a device is configured as soon as it is
connected

17. Steps taken when developing device
drivers
1. Know about the hardware. The developer should
have an in-depth grasp about the platform’s
hardware. Read the device –datasheet to understand
relevant terms and definitions. You should know the
method through which data is transferred. You should
know the software of the device-drivers resides and
what bus interface does the hardware use to
communicate with the host.
 In case the primary device is a system on chip then
developers should know how the driver interacts with
its firmware and command protocols

18. Steps cont’d
2. Write driver code. In this step, developers are
expected to come up with the a working prototype of
the preferred hardware then they should start writing
the kernel mode driver.
 If the device is incorrectly designed the driver’s
running in the user mode may cause system crash
likewise if anything goes wrong with the drivers
working in highly privileged settings, operational
concerns may occur.
 Usually, the first functions that you develop for your
Device Driver are Load and Unload functions
which are invoked when the Operating System
Starts and Shuts down respectively.

19. Steps cont’d
3.Initialise the hardware. Once you are able to
detect your hardware, the next is to initialize your
hardware. The kind of initialization that is needed
may vary for each hardware. It may range from just
writing to a couple of device registers to all the way,
downloading a microcode onto the device, and
communicating using proprietary command protocol.

20. Steps cont’d
4. Control the hardware. The next step is controlling your hardware.
Until Step 3, the operation might be a one-time operation when the OS loads, Step
4 might be needed to be performed multiple times after the Operating System is up
and running. The developer must know whether the device will simply relay data
from one device to another, they should also consider whether the device will be
sending data continuously

21. Steps cont’d
5.Begin data communication with the hardware.
Several devices deal with some form of data be it
video, audio. Once the device is initialized, the
developer can send some stream of data as
required. The driver works a as pipeline between the
high level application and the low level hardware for
data transfer.
As noted in step 1 developer should know the
protocols of data communication.

22. Steps cont’d
6.Control data communication. In this step
developers need to control data transfer and manage
data communication in several situations. When
problems arise ,the peripheral devices shouldn’t
send the same error message.
7.Test it and debug it. At this point, your driver may
be ready for testing, since all the development is
done to ensure that is initialized and recognized.
Functional tests should be run to ensure that it works
as expected.

23. References
 https://www.javatpoint.com/device-driver-in-
operating-system
 spiceworks.com/tech/devops/articles/what-is-
device-driver/
 Advanced OS by Nsereko Julius Kayongo