chin report - 2nd

8/14/2019 Chin Report - 2nd

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E X C E P T I ON S

Is often used to refer toany event that causes aninterruption


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Kinds of Exceptions

Recovery from Errors

Exception-Service Routine-takes appropriate action

to recover from the error or toinform the user about it.


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Debugging

Debugger-helps the programmer find errors

in a program.

2 important facilities of debugger:

Trace ModeBreakpoints


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Privilege Exception

Privileged Instruction-modifies the priority of the

processor.


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Operating System

Responsible for coordinating all activities within acomputer.

Makes extensive use of I/O operations.

Incorporates the interrupt-service routines for alldevices connected to a computer.

Provides a variety of services to applicationprograms.


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The OS includes:

Multitasking a mode of operationin which a processor executes severaluser programs at the same time.

Time slicing with this technique,each program runs for a short periodcalled a time slice.

OSINIT set interrupt vectors.


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SCHEDULER an OS routine whosefunction is to determine which user

program should run in the next time slice.It saves all the information that will beneeded later when the execution of aprogram is resumed.

Program State the information savedby the SCHEDULER. It includes registercontents, the program counter, and theprocessor status word.

Processor Status Word it containsthe condition flags and other informationsuch as priority level.


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PROCESS

Running the program is currentlybeing executed.Runnable the program is ready

for execution but is waiting to beselected by the SCHEDULER.

Blocked the program is not readyto resume execution for some reason.

OSSERVICES examine stack todetermine requested operation.


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IOINIT a routine that is responsiblefor starting I/O operations.

Device Driver - is a computerprogram allowing higher-level computerprograms to interact with a hardwaredevice.

IODATA poll devices to determinesource of interrupt.

END a flag that is set to 1 if thecharacter is a carriage return.


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Use of Interrupts in OS

Enables the operating system to assignpriorities, switch from one user programto another, implement security and

protection features, and coordinate I/Oactivities.

Can be used to call different parts of theOS, depending on the service beingrequested.


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Processor Examples

ARM Interrupt Structure

ARM Processor- Advanced RISC (Reduced Instruction

Set Computer) Machines has a simple yetpowerful exception-handling mechanism.


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5 Sources of ExceptionsExternal interrupt-request lines(IRQ).

Fast Interrupt Request (FIQ).

Software Interrupt Instruction(SWI).

External Abort following a bus

error.

Attempt to execute an undefinedinstruction.


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Exceptions are handledaccording to the following

priority structure:

3. Reset4. Data Abort5. FIQ 6. IRQ 7. Prefetch Abort8. Undefined Structure


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When the processor accepts aninterrupt, it takes the followingactions:

2. It saves the return address of theinterrupted program in register14 of thecorresponding mode.

3. It saves the contents of the currentprocessor status register (CPSR) in thecorresponding SPSR (Saved ProcessorStatus Register).

4. It changes the mode bits in CPSRaccording to the type of interrupt.

5. It branches to the interrupt-serviceroutine starting at the appropriate vectoraddress.


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*The ARM Processor uses a pipelined structure .

Pipelined Structure- an instruction is fetched before the

execution of the preceding instruction iscompleted.


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ARM Processor


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Stacks and Nesting

ARM Interrupt Mechanism

- stores the return address in aregister and does not automaticallyimplements a stacking mechanism toallow subroutine or interrupt nesting.

chin report - 2nd

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