Advanced Microprocessors Lab 1: What Is Interrupted B 609510

Advanced Microprocessors Lab1 What Is Interrupted By An Interrupt2

What is interrupted by an interrupt?

An interrupt is a signal to the processor indicating that an immediate attention is required. It temporarily halts the current execution of instructions to service a specific event or condition. Essentially, the part of the system that gets interrupted is the current program or process that the CPU is executing at that moment. The CPU saves its current state and then jumps to the interrupt service routine (ISR) to handle the event.

What is called by an interrupt?

When an interrupt occurs, the processor calls the corresponding Interrupt Service Routine (ISR), also known as an interrupt handler. This routine is a specific piece of code designed to manage the event that triggered the interrupt, such as input/output completion, hardware signals, or internal exceptions. The ISR performs the needed operations to respond to the interrupt, such as reading data, clearing flags, or handling errors.

List the interrupt pins found on the microprocessor.

Microprocessors typically have dedicated interrupt pins, which include:

• INTR (Interrupt Request): A general-purpose interrupt line used to request interrupt processing.
• NMI (Non-Maskable Interrupt): A high-priority, non-maskable interrupt that cannot be ignored by the processor.
• INTA (Interrupt Acknowledge): The signal used by the CPU to acknowledge that it has recognized an interrupt, often used in vectored interrupt systems.

Additional systems or microcontrollers may include other pins, but these are the primary interrupt-related pins on conventional microprocessors like the 8086/8088.

What is an interrupt vector?

An interrupt vector is a unique address in memory that points to the start of an interrupt service routine (ISR). When an interrupt occurs, the processor uses the interrupt vector to locate and execute the appropriate ISR without the need for complex address calculations. In systems with a table of interrupt vectors, each vector corresponds to a specific interrupt type or source, enabling quick and efficient interrupt handling.

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 microprocessor architecture. For example, in the 8086 microprocessor, there are 256 interrupt vectors arranged in a table at the beginning of memory, each occupying 4 bytes (2 for segment, 2 for offset), allowing for 256 different interrupt sources.

In more sophisticated systems like the x86 protected mode, the interrupt vector table can include many entries, often up to 256, each corresponding to specific hardware or software interrupts.

Explain how a type 0 interrupt occurs.

A type 0 interrupt, often associated with hardware or software exceptions, occurs when the CPU detects an event that requires immediate attention, such as division by zero, invalid opcode, or a hardware fault. In some architectures, particularly in the x86 architecture, type 0 interrupts correspond to divide-by-zero errors. When such an event occurs, the processor halts normal execution and redirects control to the specific ISR designated for handling that exception, usually via the interrupt vector table.

Each protected mode interrupt descriptor contains what information?

In protected mode, each interrupt descriptor contains the following information:

• Segment selector: points to the code segment where the ISR resides.
• Offset: the specific location within the segment where the ISR begins.
• Access rights and privilege level: defines the privilege level required to access the routine.
• Type and attributes: such as present bit, size (16/32-bit), and gate type ( interrupt gate, trap gate).

This descriptor ensures that the CPU can correctly and securely transfer control to the appropriate interrupt handler, maintaining system stability and security.

Describe the operation of the BOUND instruction.

The BOUND instruction in microprocessors is used to compare a specified register or memory operand against an array of bounds stored in memory. It is intended for runtime array bound checking. When executed, the BOUND instruction checks whether the value of the operand lies within the bounds specified by the corresponding lower and upper boundary values. If the operand exceeds these limits, an exception is raised, typically resulting in an interrupt or trap, which can be handled to prevent array overflows or invalid memory accesses. This instruction enhances program safety by adding runtime checks for array bounds.

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

In the Intel 8086 architecture, software interrupt vectors are located in the interrupt vector table starting at memory address 0000:0000. Each vector is 4 bytes long, containing the offset and segment of the ISR. For an INT 44H (hexadecimal 44), the vector's address in the table is calculated as:

V = 44H * 4 = 11Ch (hexadecimal 0x11C)

Thus, the memory locations at address 0x11C and 0x11E contain the offset and segment address, respectively, of the interrupt vector for INT 44H. Specifically, the byte at 0x11C and 0x11D give the offset, and the byte at 0x11E and 0x11F give the segment address of the ISR.

Paper For Above instruction

Interrupts are a fundamental mechanism in microprocessor systems, enabling efficient and immediate responses to events that require the processor's attention. When an interrupt occurs, it temporarily halts the current execution and invokes the appropriate interrupt service routine (ISR), a dedicated piece of code designed to address the specific event. This interruption is triggered via hardware or software signals and managed through dedicated pins such as INTR, NMI, and INTA, which facilitate communication between peripherals and the processor.

The processor uses an interrupt vector, a specific memory address pointing to the ISR, to handle these events efficiently. In typical architectures like the 8086, the interrupt vector table contains up to 256 entries, each corresponding to a different source or type of interrupt. When an interrupt happens, the processor locates the relevant vector based on the interrupt number, retrieves the address of the ISR, and transfers control to it. This process ensures rapid and organized handling of multiple interrupts, improving system responsiveness and reliability.

System exceptions, such as division by zero, are typically handled as type 0 interrupts within the architecture. These are critical conditions that require immediate attention to prevent system crashes or data corruption. In protected mode, each interrupt descriptor encompasses vital information, including the segment selector, offset, privilege level, and access rights, facilitating secure and correct control transfer to the ISR. Gate types such as interrupt gate or trap gate dictate how the CPU manages privilege levels and stack states during the transfer.

The BOUND instruction serves a critical role in runtime safety, allowing programs to verify that array indices or other data values lie within specified bounds. If the bounds check fails, an exception is raised—usually triggering an interrupt or trap—protecting against buffer overflows and memory corruption. This feature is especially important in systems programming and high-reliability applications.

Regarding the memory locations for specific interrupt vectors such as INT 44H, the vector resides within the interrupt vector table at an address computed by multiplying the vector number by four. For INT 44H, corresponding to hexadecimal 0x44, the vector's address is at 0x11C in the table, containing the offset and segment for the ISR. Such precise memory arrangements enable swift access to ISRs, crucial for high-performance system operation.

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