i have provided everything about interupt.

1. Saleem
Mahar

2.  What Are Interrupts?
 Why Interrupts?
 Instruction Cycle And Interrupts
 Difference b/w Interrupts and Exceptions
 Classes Of Interrupts
 How They Are Handled?
 I/O Communication Techniques
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3. 3
 A Suspension of a process such as the execution
of a computer program, caused by an event
external to that process, and performed in such a
way that the current process can be resumed.
 A way to improve processor utilization.

4. 4
 The OS is a reactive program
 When you give some input
 It will perform computations
 Produces output BUT
 Meanwhile you can interact with the system by
interrupting the running process or
 You can stop and start another process.
 This reactive ness is due to interrupts
 Modern Operating Systems Are Interrupt driven

5.  Without Interrupts
 Two steps ( cycles)
 Instruction Fetch
 Instruction Execute
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6.  State Diagram
( Without Interrupts)
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7. (Continued)
 With Interrupts
 Three steps ( cycles)


 Instruction Fetch
Instruction Execute
Check Interrupt
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8.  State Diagram ( With
Interrupts)
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9. 9
 Two main types of events: interrupts and
exceptions
 Exceptions are caused by software executing
instructions

 e.g., a page fault, or an attempted write to a read-
only page
an expected exception is a “trap”, unexpected is a
“fault”
 Interrupts are caused by hardware devices
 e.g., device finishes I/O

10. 10
 Program
 Generated by some condition that occurs as a result of an
instruction execution, such as arithmetic overflow,
division by zero, attempt to execute an illegal machine
instruction etc.
 Timer
 Generated by a timer within the processor. This allows the
operating system to perform certain functions on a regular
basis.
 I/O
 Generated by an I/O controller, to signal normal completion
of an operation or to signal a variety of error conditions.
 Hardware failure
 Generated by a failure, such as power failure or memory parity error.

11. 11
 Different routines handle different interrupts –
called Interrupt Service Routines (ISR).
 When CPU is interrupted
 It stops what it was doing, and context is saved.
 A generic routine called Interrupt Handling
Routine (IHR) is run which
 Examines the nature of interrupt
 Calls the corresponding Interrupt Service Routine
(ISR) -- stored in lower part of memory.
 After servicing the interrupt, the saved address
is loaded again to PC to resume the process
again.

12. 12

13. ts By: Irfanullah University Of Peshawar, 13
(Continued)
 Interrupt
Processing

14. 14
 Three techniques are possible for I/O operations
 Programmed I/O
 Interrupt-driven I/O
 Direct memory access (DMA)

15. 15





CPU while executing a
program encounters an I/O
instruction
CPU issues I/O command to I/
O module
I/O module performs the
requested action & set status
registers
CPU is responsible to check
status registers periodically to
see if I/O operation is
complete. SO
No Interrupt to alert the
processor

16. 16
 Similar to direct I/O but
processor not required
to poll device.
 I/O module will interrupt
CPU for data exchange
when ready

17.  Requires DMA module on system bus
 Capable of mimicking CPU and taking over
control of system from CPU
 DMA will use bus when
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 I/O exchanges occur directly with
memory



 Processor does not require it
OR
Must force processor to
suspend operation
temporarily– called cycle
stealing


An interrupt is sent when the task
is complete
The processor is only involved at
the beginning and end of the
transfer