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IOCTL and Device drivers:

Character Devices And Block Devices

By: Bharat Parmar

Roll No: 195M.E I (MSA)

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80x86 I/0 Ports

Any I/O device is hosted by one, and only one bus.

The bus type affects the internal design of the I/O device,as well as how the device has to be handled by the kernel

The data path that connects a CPU to an I/O device isgenerally called an I/O bus.

The 80 x 86 microprocessors use 16 of their address pinsto address I/O devices and 8, 16, or 32 of their data pins to

transfer data.

The I/O bus, in turn, is connected to each I/O device bymeans of a hierarchy of hardware components..

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IOCTL Functions

IOCTL functions are used to control I/Odevices.

IOCTL do not mean Transfer Of Data.

Data transfer can take place through DOS or

BIOS or Drivers.

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Types of Devices

Devices are classified in Two Types

Character Devices: Process single Bit at atime.

Examples are.. Keyboard, Mouse, Printer.

Block Devices :Process block of Datasimultaneously

Examples.. Disk Drive, CDROM.

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Split view

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Character Devices

They are controlled in either Binary or ASCIImode by IOCTL functions.

They are named using DOS conventions.

They are opened with file open function3DH.

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IOCTL character device names

Name Device

AUX The COM1 Device in most systems

CLOCK$ The real time system clockCOM1 Serial communications port number 1COM2 Serial communications port number 2COM3 Serial communications port number 3COM4 Serial communications port number 4

CON Console, the keyboard for Input and the videodisplay for output

EMMXXXX0 The expanded memory manager EMM386.EXELPT1 Parallel Port Number 1LPT2 Parallel Port Number 2

LPT3 Parallel Port Number 3LPT4 Parallel Port Number 4NUL A Nonexistent DevicePRN LPT1 in Most systemsXMSXXXX0 The Extended Memory Manager HIMEM.SYS

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Block Devices

Block Devices transfer information block at a time

They are indicated using numbers.

BL---

00HDefault Block Device

01HBlock Device A

02H Block Device B.

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Device Driver

Special programs installed by CONFIG.SYS tocontrol installable devices.

Used for the newly added device

It is a .COM file ( TINY model )

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DEVICE DRIVER

Device Driver

Header Strategy Procedure Interrupt procedure

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Interrupt procedure

Strategy procedure

Driver Name

(8 bytes)

Interrupt offset address

Strategy offset address

Attribute

Driver linkage

Construction of a device driver

0012H

000AH

0008H

0006H

0004H

Header

0000H

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HEADER

Contains pointers that allow it to chain toother drivers loaded in the system.

First doubleword (-1) informs that this is lastdriver in chain.

It is followed by attribute word, whichindicates type of header included for driverand type of device the driver installs.

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Device Driver Attribute Values

| F | E | D | C | B | A-7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 |

| | | | | | | | | | | | `-- 1 = character device is stdin

| | | | | | | | | | | | 1 = block dev supports generic IOCTL

| | | | | | | | | | | `---1 = character device is stdout

| | | | | | | | | | | 1 = block dev supports generic IOCTL

| | | | | | | | | | `---- 1 = current NUL device

| | | | | | | | | `----- 1 = current clock device

| | | | | | | `-------- reserved by DOS

| | | | | | `--------- 1 = supports Get/Set logical device

| | | | | `----------- reserved (must be zero)

| | | | `------------- 1 = supports removable media

| | | `-------------- reserved (must be zero)| | `--------------- 1 = non-IBM format (block device)

| | 1 = output until busy (char device)

| `---------------- 1 = supports IOCTL strings

`----------------- 1 = character device, 0 = block device

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Strategy Procedure

It is called whenever device driver is loadedin to memory or whenever I/O requests areissued.

Its main purpose is to save the Request

header and its address.

Return Status Word Communicatesinformation back to DOS from Device Driver.

Device Driver Commands in Request Header By DOS

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Device Driver Commands in Request Header By DOS

Command Purpose

00H Initialize Driver 01H Media Check

02H Build BPB (Block Device Parameter Block) 03H Control Read 04H Read 05H Non destructive Read 06H Input StatusInput Status 07H Input FlushInput Flush 08H WriteWrite 09H Write with verifyWrite with verify 0AH Output StatusOutput Status 0BH Output FlushOutput Flush 0CH Control writeControl write 0DH Open DeviceOpen Device 0EH Close DeviceClose Device

0FH Removable MediaRemovable Media 10H Output until BusyOutput until Busy 13H Generic IOCTLGeneric IOCTL 17H Get logical DeviceGet logical Device 18H Set logical DeviceSet logical Device 19H IOCTL QueryIOCTL Query

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INTERRUPT PROCEDRE

It uses request header to determine thefunction requested by DOS.

It performs all functions for Device Driver

Interrupt Procedure is different from

Interrupt Handler.

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