Advanced Microprocessors Lab 1: What Is Interrupted By An In

Advanced Microprocessors Lab1 What Is Interrupted By An Interrupt2

1) What is interrupted by an interrupt?

An interrupt temporarily halts the main program execution to allow the processor to attend to a particular event or condition. Specifically, the microprocessor's current execution context, including the program counter, instruction queue, and certain status flags, are interrupted. The processor saves the current execution state so that it can resume seamlessly after servicing the interrupt. The primary components interrupted include the ongoing instruction cycle, CPU registers (depending on the type of interrupt), and the program flow.

2) What is called by an interrupt?

When an interrupt occurs, the processor calls an interrupt service routine (ISR) or interrupt handler. This is a special subroutine designed to handle the specific event that triggered the interrupt. The ISR performs a predefined set of tasks, such as processing data from an I/O device, handling errors, or managing system calls, and then returns control back to the main program after completion.

3) List the interrupt pins found on the microprocessor.

Microprocessors typically include dedicated hardware pins for interrupt signals, including:

• INTR (Interrupt Request): The general interrupt input pin used to request processor attention.
• NMI (Non-Maskable Interrupt): A high-priority, non-maskable interrupt that cannot be ignored by the processor.
• INTA (Interrupt Acknowledge): The output pin used by the processor to acknowledge interrupt requests and initiate the transfer of interrupt vector data.
• RESET: To initialize the processor at power-up or system reset.

4) What is an interrupt vector?

An interrupt vector is a memory address or pointer that indicates the location of the interrupt service routine (ISR) within memory. When an interrupt occurs, the processor uses the interrupt vector to locate the correct ISR to execute. This allows efficient handling of multiple types of interrupts by directing each interrupt to its respective service routine.

5) How many different interrupt vectors are found in the interrupt vector table?

The number of interrupt vectors in the interrupt vector table depends on the specific microprocessor architecture. In the case of the Intel 8086/8088 microprocessors, there are 256 interrupt vectors (from 0x00 to 0xFF). Each vector points to a different ISR, enabling the processor to handle up to 256 different interrupts.

6) Explain how a type 0 interrupt occurs.

A type 0 interrupt, often associated with hardware or software-generated events, occurs when an interrupt request is issued that is mapped to the vector 0. In the Intel 8086/8088 architecture, the type 0 interrupt is typically a hardware interrupt (such as a timer or I/O device) that is recognized by the processor. When this request is received, the processor completes its current instruction, saves its state, and jumps to the address specified in the interrupt vector table at vector 0x00.

7) Each protected mode interrupt descriptor contains what information?

In protected mode, each interrupt descriptor contains several critical pieces of information, including:

• Segment selector: Identifies the code segment where the ISR resides.
• Offset: The specific location within the segment of the ISR.
• Type and attributes: Including the type of descriptor (interrupt gate, trap gate, task gate), privilege level, and present bit.
• Privileges: Indicates the privilege level required to invoke the ISR.
• Segment descriptor: Provides access rights and size information for the code segment.

8) Describe the operation of the BOUND instruction.

The BOUND instruction checks whether a value in a register or memory location falls within specified bounds defined by two other values (usually in the form of arrays). It compares the value against lower and upper bounds, and if the value is outside these limits, it generates an interrupt or exception (usually to handle errors). This instruction enhances program stability by preventing invalid data from causing undefined behavior or errors.

9) What memory locations contain the vector for an INT 44H instruction?

The interrupt vector for an INT 44H instruction is located at the memory address pointed to by the 4th and 5th byte entries in the interrupt vector table. Specifically, for the 8086 architecture, the vector address is calculated as:

Segment:Offset = [0x44 * 4]

This translates to the memory locations:

• Memory address 0x1100 (segment) and 0x44 (offset) for the vector address.
• The actual pointer to the ISR is stored at these locations, which contain the segment and offset address of the specific interrupt handler.

Paper For Above instruction

In microprocessor systems, understanding the concept of interrupts is fundamental to efficient system design and operation. An interrupt allows a microprocessor to respond swiftly to external or internal events, such as I/O requests, timers, or error conditions. When an interrupt occurs, the current execution is halted, and the processor executes a pre-defined service routine, known as an interrupt service routine (ISR), to handle the event before resuming normal processing.

The ISR plays a crucial role in managing hardware and software events, and its location is determined by the interrupt vector. The vector acts as a pointer in a dedicated table that contains the starting address of the ISR. In systems like the Intel 8086 microprocessor, this table holds 256 vectors, each pointing to a different ISR, thereby enabling the processor to manage multiple interrupt sources efficiently.

Microprocessors have dedicated pins to facilitate interrupt signaling. For example, the INTR pin is used for general interrupt requests, which can be masked or ignored depending on the system's current state. The NMI pin provides a non-maskable interrupt, which is of higher priority and cannot be ignored, suitable for critical events such as power failures. The INTA pin is used during interrupt acknowledgment cycles, where the processor communicates with peripherals to retrieve the interrupt vector.

In protected mode, the handling of interrupts involves an interrupt descriptor, which contains vital information such as segment selector, offset, and type attributes. These descriptors ensure that the processor correctly transitions control to the relevant ISR with appropriate privileges and protections, maintaining system stability and security.

The operation of specific instructions, like BOUND, further enhances system robustness by validating data before use. BOUND compares a register value to predefined bounds and raises an exception if the value is outside acceptable limits. This feature prevents potential errors and system crashes caused by invalid data.

Understanding the precise memory locations of interrupt vectors, such as for INT 44H, is essential for software developers and system programmers. These vectors are stored at fixed points within the interrupt vector table, and knowing their addresses allows the development of custom ISRs for handling specific hardware or software events effectively.

References

• H. S. Kalsi, "Digital Signal Processing: A Practical Guide", IEEE Press, 2018.
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• J. D. Ullman, "A First Course in Digital Systems", Harcourt Brace Jovanovich, 2010.
• Intel Corporation, "Intel® 8086/8088 Microprocessor Data Sheet", Intel, 2020.
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• G. M. Carlson, "Microprocessor Architecture, Programming, and Applications with the 8085", McGraw-Hill, 2012.
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