Microprocessor Interrupts and DMA

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Questions and Answers

What is a characteristic of a maskable interrupt?

It cannot be disabled or ignored by the CPU.

It is used for emergency purposes.

It can be disabled or ignored by CPU instructions. (correct)

It is exclusively generated by hardware devices.

Which of the following best describes a non-maskable interrupt?

It occurs only during software execution.

It can be disabled by user programs.

It is critical and cannot be ignored by the CPU. (correct)

It is a signal from a peripheral device.

Which statement is true regarding hardware interrupts?

Every keystroke can generate an interrupt signal. (correct)

They are typically generated by programs.

They only occur when the system crashes.

They cannot be generated by external devices.

What is the primary advantage of Direct Memory Access (DMA)?

It allows the CPU more time to execute other processes. Signup and view all the answers

Which type of interrupt is generated by unexpected critical events?

Software interrupt Signup and view all the answers

In what scenario would a non-maskable interrupt commonly be used?

To manage power failure events. Signup and view all the answers

Which of the following is a true statement about software interrupts?

They can initiate exceptions like faults and traps. Signup and view all the answers

How does Direct Memory Access (DMA) improve data transfer efficiency?

By allowing devices to send data directly to memory. Signup and view all the answers

What is the main function of the 'C' bit in the status register?

Indicates a carry or borrow was generated Signup and view all the answers

Which of the following allows user mode access to perform all operations except for privileged instructions?

User mode Signup and view all the answers

Which condition code is set when the result of an operation is zero?

Z Signup and view all the answers

What characterizes an interrupt that is strictly prioritized in the CPU?

Higher-numbered interrupts can interrupt lower-numbered ones Signup and view all the answers

Which bit in the status register is retained for multi-precision arithmetic?

X Signup and view all the answers

What happens to interrupts when the CPU operates in supervisor mode?

All interrupts become supervisory Signup and view all the answers

Which of the following describes the extend (X) flag in the condition code register?

Tracks the last carry out of the most significant bit Signup and view all the answers

What is the purpose of having a separate stack pointer for supervisor privilege level?

To facilitate multitasking with smaller memory allocation Signup and view all the answers

What is the function of a non-maskable interrupt (NMI)?

It can interrupt processes at any time regardless of the current interrupt level set. Signup and view all the answers

Which level of interrupt can be interrupted by any higher priority interrupt?

Level 1 Signup and view all the answers

What technique is used in I/O operations where the CPU has full control?

Direct Transfer/Programmed I/O Signup and view all the answers

Which flag in the status register indicates whether an arithmetic operation resulted in a negative value?

Negative Flag Signup and view all the answers

Which of the following techniques allows multiple devices to access memory independently of the CPU?

Direct Memory Access Signup and view all the answers

Which of the following interrupts is typically used for handling urgent events that require immediate attention?

Non-maskable Interrupt Signup and view all the answers

In the context of interrupts, what does blocking mean?

Preventing lower or equal priority interrupts from occurring. Signup and view all the answers

What best describes the role of the Program Counter in a CPU?

It keeps track of the current instruction line of a program. Signup and view all the answers

Study Notes

Interrupts

An interrupt is a signal that stops the microprocessor from its current task so that another task can be performed.
Interrupts can be hardware or software based.
Hardware interrupts are generated by peripheral devices, such as a keyboard, a printer, or a mouse.
Software interrupts are generated by the operating system or by a program.
Hardware interrupts can be maskable (disabled or ignored by the CPU) or non-maskable (cannot be disabled or ignored by the CPU).
Maskable interrupts are used to interface with peripheral devices.
Non-maskable interrupts are used for emergency purposes, such as power failure or smoke detectors.

Direct Memory Access (DMA)

DMA allows a device to directly transfer data to main memory without involving the CPU.
DMA bypasses the CPU and transfers data in one step, making it more efficient than the two-step process used by the CPU.

68000 Processor

Status Register:
- 16-bit register used by the CPU to indicate the condition of the microprocessor.
- The upper 8 bits are the system byte (privileged).
- The lower 8 bits are the user byte, also known as the Condition Code Register (CCR) (not privileged).
- The CCR includes five condition code bits: Carry (C), Overflow (V), Zero (Z), Negative (N), and Extend (X).
Program Counter:
- A 24-bit counter that monitors the instruction line of a program.

Privilege Levels

The 68000 processor implements two levels of privilege:
- User Mode: Access to everything except privileged instructions.
- Supervisor Mode: Access to everything.
An interrupt always becomes supervisory.
The supervisor bit is stored in the status register.
Supervisor mode has a separate stack pointer, which allows multitasking systems to use smaller stacks.

Interrupts (68000)

The 68000 processor recognizes seven interrupt levels (1-5, 7).
Higher numbered interrupts have higher priority and can interrupt lower priority interrupts.
Level 7 is a non-maskable interrupt (NMI).
Level 1 can be interrupted by any higher level.
Level 0 means no interrupt.
The interrupt level is stored in the status register.

Data Transfering Technique (DTT)

Three methods are possible for I/O operations:
- Direct Transfer (Programmed I/O): The CPU is fully involved and controls the I/O operation.
- Interrupt: The CPU is interrupted by the device to handle the I/O operation.
- Direct Memory Access (DMA): The device directly transfers data to memory without involving the CPU.

Direct Transfer (Programmed I/O)

The CPU directly executes instructions that control the I/O operation.
The CPU continuously checks the status of the I/O module to determine if the operation is complete.

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Description

This quiz explores the concepts of interrupts, including hardware and software types, and the significance of Direct Memory Access (DMA) in microprocessors. It delves into the function and use of maskable and non-maskable interrupts, as well as the efficiency of DMA in bypassing the CPU for data transfers.