Transcript Assembly Language Lecture 21-23 Presented By Shery khan 10:00 to 11:00 [email protected] www.sherykhan.jimdo.com Agenda ► What are interrupts? ► What are types of Interrupts? ► Working of Interrupts? ► Software & Hardware.

Assembly Language
Lecture 21-23
Presented By
Shery khan
10:00 to 11:00
[email protected]
www.sherykhan.jimdo.com
Agenda
► What
are interrupts?
► What are types of Interrupts?
► Working of Interrupts?
► Software & Hardware Interrupt?
► Hooking An Interrupts?
► Bios & dos Interrupts?
► Hardware Interrupts?
► Example…..
What are interrupts?
► INT
are ASYNCHOROUS & Unpredictable
► Current State of Processor or Working is Not
Disturbed or Currently Executing Instruction
► Asynchronous mean which point of instruction
were instruction is Executed.
► Un predictable : means at which time interrupt will
come
► IN Generally : the event that occur outside the
processor and the processor must be informed
What are types of Interrupts?
► 8088
processor divides it in two major
classes
► Software Interrupts
► Hardware Interrupts
Hardware INT: Generated by External world
Software INT: Not Generated by External
world they are just Extended Far Call
Extended Far Call: Push Segment+offset+Flag
Continue:
► Why
Flag is Saved ?
► Sunario is That let suppose I want to Compare two
instruction and Then Jump but in between
Interrupt comes here comparison is done but not
performed Jump instead processor now execute
interrupt routine now there Flag registers are
changed now I return on actual instruction
► Here the Jump will be the Instruction but Jump
will not be legal because Flags are Changed in
Interrupt routine . So to avoid this we save Flags.
IVT
► When
ever Interrupt comes some operation is
done in arrival of Interruption
► So the Relation between Interrupt and Operation
is performed on the basis of Interrupt vector table
► Boiler Example like that When Temperature
Increases The Interrupt Signal is Invoked and
Processor Will read this Interruption and do some
operation to reduce the Heat of Boiler . So Arrival
of Interrupt Processor take Action
ISR/HOOK
► So
every Interrupt we can made we can
build a routine in relation with interrupt
which we can called as Interrupt Service
Routine .or we say the Mechanism for
Interrupt to served is called ISR
► The Co-Relationship between Interrupt and
Interrupt service routine is Generally called
HOOKING
Syntax
► INT
n
► Here we use Int key word with num in byte
► INT 0-255
► Number tells us which Interrupt is used to achieve
the respective results
► INT opcode is CD and the Num is Co-related to
Interrupt to route the service routine(ISR)
► IT IS 2 BYTE
RESERVED INTERRUPTS
► Generally
we do not use these Reserved INT
► Because these are related to processor
Like INT 0 is divide by zero Int
Such interrupts are programmed in the
hardware to generate the designated
interrupts when specific condition arises
Co-relation INT & Num
► We
use a Table IVT
► IVT Location is Fixed to Physical Memory
address zero
► Each Entry of Table is four Byte long contain
the segment & offset of Interrupt routine for
corresponding interrupt Number
► First two byte Contain Offset
► Next Two Segment
Continue
► Mathematically
offset of the Interrupt n will
be n*4 while segment will be n*4+2
► One entry in this table is called Vector
► So Here vector for INT 0
► Is 0*4=4
► Int 0
► 0,1,2,3 Colored Vectors are offset
► 2,3 is Segment
continue
► INT
1
1*4=4
So 4,5,6,7
► INT 2
► 2*4=8
► So 8,9,10,11
► Int 3
► 2*3=6 --------------?question
► respectively
Working of INT
► First
Push the Flag Register
► Secondly Push the CS Segment Register
► Then IP is Pushed to Stack
► Here two flags Automatically IF=0,TF=0
► So the other Up coming Interrupts are
Disable When One is In IVT Table so First
come First Served Basis Other are Not
allowed Disabled
continue
► After
these step the ISR is Called and
Control goes to Interrupt service Routine
► For Returning from this Routine Use iret
Story
► When
An interrupt arrived Processor take Action
and go to IVT table and Call the Routine after
Some Specific Operation it Return and How it can
Return we Use IRET
► iRet for this Purpose
► Iret is Working Reverse first
► POP the IP into Ip
► Pop the CS
► POP the Flag
Why we not use Ret Far instead of
Iret???
► Ret
Far not use it is used when we use Call
far
► And Ret Far take 2 words IP,Cs leave the
Flag
► So we Can use IRET
Working Int N
► Push
► IF
► TF
► Push
flag
0
0
cs
► IP [0:4*n]-------------------offset
► Cs [0:4*n+2]------------ Segment
► ISR Execute
Iret
► Ip
► SP
[ss:sp]
sp+2
► Cs [ss:sp]
► Sp +2
► Flag [ss:sp]
► Sp sp+2
► Control return to Next instruction which is
pointed by IP
Example
Example
Example
Example
Example
Example
Example
Example
Lecture 22
► For
Example
► BOOK with its Content in Start Like
► Chapter 4 started from Page 240
► Here Page 240 is Vector and Chapter 2 is
Interrupt so the Processor go the page 240
Not 220 so in IVT has 256 chapter and
Interrupt mechanism look up appropriate
chapter num to read the desire page and
find the Interrupt routine
VECTOR TABLE
► In
table Content are Fixed always placed at
the start of book so same case the Vector
table position is fixed zero for IVT and
occupy exactly 1 kilo byte of memory
► 256*4=1kb 256 is num of possible
interrupts while size of one vector is 4 byte
IVT
Software / Hardware INT
► Software
Interrupt Break the program flow
► Un programmed interruption is Hardware Int
Reserved Interrupts of 8088
INT 0
INT 1
INT 2,INT 3,INT 4
These Five Interrupts are automatically tied with
processor
INT 0
► Is
Same as when we Divide by 0
► We know that when quotient did not fit in
the destination register let say div Bl
► Quotient in AL
► Reminder Ah Divide Overflow
► System automatically call INT 0 Invoke
when Divide Overflow
INT 1 (TRAP FLAG)
► Debugger
Pressed F1
► Trap Flag INT 1 Invoked
► F1
► Trap Flag INT 1 Invoked
► Its set Trap flag and Disable other Interruption it is
automatically generated after every instruction .
► Used for single stepping
it is working like that sir one Instruction is executed
now tell me what I can do
INT 2 (NMI)
► Non
Mask able Interrupt Real interrupt Comes
Outside the processor
► Two Pins in the processor INT Pin & NMI PIN
► INT Pin Processor can be directed to lesson or not
to listen
► NMI PIN tells about Fetal hardware Failure in the
System
► Int Pin Can be Masked or ignored
► NMI pin Cannot be Masked
► Like Castrophic (Natural Disaster ) Comes and
Processor must Listen and do Some Operation
INT 3 Debug Interrupt
► Single
byte Opcode CC
► Replace any Instruction with Break Point
► It is Software Interrupt
► Detail is in Debugger Topic
INT 4 (Arithmetic Overflow)
Change of Sign Bit
It is Invoked when Unexpectedly sign Bit is Changed as a
result of mathematical or logical instruction
► Overflow Flag signals a real overflow only if the number is
treated as signed Number
► Not Automatically generated But as a Result of Special
Instruction INTO (Interrupt on Overflow) if overflow flag is
Set otherwise INTO behave as NO Operation (NOP)
► Review of OVERFLOW FLAG:
► Overflow flag is set during signed Arithmetic e.g
► addition or subtraction When the when the sign of
destination changes Unexpectedly
►
DIVIDE OVER FLOW
Lecture 23
INTERRUPTS
BIOS And DOS Interrupts
► Bios
provide Basic Building Block and DOS /OS
Work on it & provide different Interfaces
► BIOS (basic Input output Services)
► When Computer is Switch on BIOS get control to
a specified address
► For Booting Some Hardware Tests (Key Board ,
Hard drive etc) Are performed Boot time on
screen giving BIOS Version , Detecting Basic
Hardware .and then BOOT strap mean that Load
OS from Hard disk & from there OS take Control &
process to load its Components and Display a
Command Prompt in the End
Continue
► There
are two important programs OS &
BIOS
► OS services are high level and Work on Bios
► Bios Services are Low level
► Direct Controlling the hardware is Further
Low Level
► WE USE VIDEO By direct controlling Video
Memory By passing BIOS
BIOS SERVICES
► BIOS
services are Optionally with us .if we
do not use there is no limitation on us we
go & By Pass these Layer and access
Hardware directly
► Sometime Bios Did Not Provide Some Sort
of Services So we By Pass BIOS layer DOS
Layer and Straightly go to Hardware
USELESS
If BIOS did not Communicate With our program it is
Useless so there Must some Mechanism way to
communicate
► So we use INTERRUPT MECHANISM
Interrupts Provide a standard interrupt Num for
Caller & Flexibility to place A routine Anywhere in the
Memory
So INT 10 Video Services
INT 16 Keyboard Services
So Manufacturer place Code where ever he want and
Service are exported
►
BIOS/ DOS SERVICES
► Keyboard
Services are Exported through INT 16
► Parallel Port Services Through INT 17
► DOS has Single Entry point Through INT 21
► The Sub services Concept Lies here Every Service
Number has Further Sub Services
► Like INT 10 (VIDEO SERVICES)
► 00 For Video
► 01 for Set cursor size
► ……
BIOS SERVICES
► Services
Num Is Usually given in AH Register
While Sub service Num is In AL or BL
BIOS INTERRUPT SERVICES:
INT 0x10 Video Service
INT 0x13 Disk Service
INT 0x14 Serial Port Service
INT 0x16 Key board Service
INT 0x17 Parallel Port Service
INT 0x1A Time & Date Service
0x10 Video SUB SERVICES
► 0x00
► 0x01
► 0x02
► 0x06
► 0x07
► 0x13
Video Mem
Set Cursor Size
Set Cursor Position
Scroll Screen Up
Scroll Screen Down
Write Character String
Example Cursor Screen Up
0x06 sub service
Summary
► INTERRUPTS
► RESERVED
INTERRUPTS
► BIOS & DOS INTERRUPTS
THE END :
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