Device Drivers

Device Drivers
Writing UNIX Device Drivers
George Pajari
Chapter : 1,2,5,13
Design and anatomy of UNIX device driver:
Types of device driver
General design of UNIX character device driver
General design of UNIX block device driver
UNIX device driver installation.
Chapter - 1
What is Device Driver ??
What is Device Driver ?
A Device Driver is glue between an OS and its
I/O devices.
Act as Translators, Requests to Command etc.
Device drivers communicate directly with
A device is a physical or logical entity that
requires control, resource management, or both
from the operating system (OS).
A device driver is a software module that
manages the operation of a virtual or physical
device, a protocol, or a service.
What is Device Driver ?
Major Design Issue
OS / Driver Communication
Exchange information (command and data)
Support functions that the kernel provides
Driver / Hardware Communication
Exchange information (command and data)
Software talks to the hardware
Hardware talks to the software
Driver Opertaions
Interrupting ,scheduling, managing, read, write,
Types of Device Drivers
Block Drivers
Character Drivers
Terminal Drivers
Stream Drivers
Block Drivers
It communicate with OS through a collection of
fixed-sized bufferss.
For example, disks are commonly implemented as block devices.
Character Drivers
It can handle I/O requests of arbitary size.
Mostly used devices, Pritners
Terminal Drivers
Same as character drivers to deal with
communication terminals that connect users to
STREAM Drivers
It can handle high speed communication
devices such as networking adapters that deal
with unusal sized chunks of data and that need
to handle protocol.
It is also known as Network Device Drivers.
eg. Network Devices
Chapter - 2
Charcter Driver I – A Test Data Generator
Character Driver : Entry Points
init( ): Initialize hardware
start( ): Boot time initialization (require system services)
open(dev, flag, id): initialization for read or write
close(dev, flag, id): release resources after read and
halt( ): call before the system is shutdown
intr(vector): called by the kernel on a hardware interrupt
read/write calls: data transfer
poll(pri): called by the kernel 25 to 100 times a second
ioctl(dev, cmd, arg, mode): special request processing
Character Driver : Prologue
It includes all of the definition and declarations
required by the driver.
Three types of Prologue :
Reference to the header files (Data types / Structures)
Definitions that local for driver
Declaration local to the Driver
Reference to the header files
#include <sys/types.h>
#include <sys/param.h>
#include <sys/dir.h>
#include <sys/signal.h>
#include <sys/errno.h>
All above header files are found in the directory
/usr/include/sys and read before writing first
Header files example
Sys/types.h : contain variaous data types
Sys/param.h : contain definition of various kernel
parameter and macros that are needed by
Sys/dir.h : contains definition of directory structure
Sys/signal.h : contains the definition related to
signals needed by sys/user.h
Sys/user.h : contains the definition of user
Sys/errno.h : contains the definition of various
Init() Entry Point
To check device actually installed on the machine
To print message (Presence / Absence)
Initialize device (Prior to open)
Allocate Local Memory
It is optional entry point
Chapter - 5
Block Drivers I : A Test Data Generator
Block Drivers - Prologue
#include <sys/types.h>
#include <sys/buf.h> - Definition of buffer header
that are used to coordinate the transfer of data
to and from block drivers.
#include <sys/cmn_err.h> - definition used by the
error reporting routine.
Block Drivers – Entry Points
Strategy() - Responsible for handling requests for
data (in or Out) and replace both the read and
write entry points found in character drivers.
Print() - it to used by the kernel report problems
related to the driver. It needs to print the error
message on the console and usyally calls upon
the kernel routine cmn_err() to display message.
Chapter - 13
Driver Installation
Driver Installation Steps
Compiling the device driver
Modifying the kernel configuration tables and files
Linking the device with the kernel object files to
produce a new kernel
Creating the necessary entries in the /dev
Rebooting the system with the new kernel.
Compiling the driver
It is similar to compiling any other C Program.
Driver is not a stand-alone program, It is always
compiled to produce an Object rather than a
linked executable file.
It need to linking in to the kernel.
Necessary information obtained from system's
Configuing the Kernel
Kernel Configuration tables to reflect the addition
of new driver.
Method varies between different Version of Unix.
There are two Config files used by the system to
generate a new kernel are the mdevice and
sdevice file contain entry for each device driver
that exists on the system.
Sdevice contains info for each device driver that is
to be incorporated into the kernel
Mdevice contains entry for each device driver that
exist on the system.
Mdevice file
Device Name
Fucntion List
Driver characteristics
Handle Prefix
Block Major Number
Character Major Number
Minimum Unit
Maximum Unit
DMA Channel
Sdevice file
Device Name
Interrupt Type
Start I/O Address
End I/O Address
Start Controller Memory Address
Building a New Kernel
Sytem utlity to run is idbuild.
Creating Entries in /dev
/dev directory that reference your device driver.
It can be done with mknod command.
On most system it will be automatically.
Node files has four fields.
Device Name
Node Name
Node Type
Minor Device Number
Rebooting the New Kernel
Reboot the system
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