Professional Courses
Industry-relevant training in Business, Technology, and Design to help professionals and graduates upskill for real-world careers.
Categories
Interactive Games
Fun, engaging games to boost memory, math fluency, typing speed, and English skills—perfect for learners of all ages.
Typing
Memory
Math
English Adventures
Knowledge
Enroll to start learning
You’ve not yet enrolled in this course. Please enroll for free to listen to audio lessons, classroom podcasts and take practice test.
Interactive Audio Lesson
Listen to a student-teacher conversation explaining the topic in a relatable way.
Understanding Interrupts
Unlock Audio Lesson
Today, we'll start by discussing interrupts in the context of instruction execution. Can anyone tell me what happens when an interrupt occurs?
I think it means that the CPU has to pause what it's doing to handle a specific request from hardware or I/O devices.
Exactly right! When a hardware device needs urgent attention, the current instruction sequence is interrupted. This allows the system to handle the interrupt effectively. Can anyone explain what we need to do with the Program Counter during an interrupt?
The value of the Program Counter needs to be saved so that we can return to it after handling the interrupt.
That's correct! We save the PC in a stack to remember where to continue from after the interrupt is addressed.
Is the interrupt service routine where we actually process the interrupt?
Yes, that's right! After saving the PC, we jump to the Interrupt Service Routine, or ISR, where we run the necessary code to handle the interrupt. Let's summarize: interrupts pause code execution and require saving the PC value so we can return to it later.
Instruction Cycle Overview
Unlock Audio Lesson
Next, we will discuss the instruction cycle. Who can tell me the stages of the instruction cycle?
I think there are fetching, decoding, and executing phases.
Correct! The instruction cycle consists of three main phases: fetch, decode, and execute. Let's break this down further. What happens during the fetch phase?
The instruction is retrieved from memory and loaded into the instruction register.
Precisely! During the fetch phase, the instruction is fetched based on the address stored in the Program Counter. Once fetched, we move to the decode phase. What happens here?
In the decode phase, the CPU interprets the instruction and prepares to execute it.
Exactly. After decoding, we advance to the execute phase. What do we do here?
The CPU performs the actions required by the instruction, like performing calculations or accessing memory.
Spot on! At the end of the execute phase, we then check for any interrupts before we move on to fetch the next instruction, ensuring a smooth operation. In summary, the instruction cycle is crucial in executing instructions effectively.
Handling Interrupts
Unlock Audio Lesson
Now let's dive deeper into how interrupts are handled. Who remembers what we do with the Program Status Word (PSW) during an interrupt?
Do we also save that before jumping to the interrupt service routine?
Correct! Along with the PC value, we also save the PSW to preserve the state of the processor. Can anyone describe the significance of the instruction cycle code (ICC)?
The ICC indicates which phase the instruction is currently in, like fetching or executing.
Exactly! The ICC helps the CPU keep track of its current activity, especially critical during interruptions. So, let's summarize: We save both the PC and PSW before addressing interrupts and use the ICC for phase tracking.
Practical Example of User Program and Interrupt Handling
Unlock Audio Lesson
To solidify our understanding, let’s consider a practical example. If we had a user program running and an interrupt occurred, what would happen?
First, the CPU would check if the current instruction is complete before handling the interrupt.
Correct! The CPU only checks for interrupts after completing an instruction to avoid complications. Can anyone explain how the flow proceeds from there?
If there is no interrupt, the process continues as usual. But if there is an interrupt, we save PC and jump to the ISR.
Exactly! After servicing the interrupt, the PC value is restored, allowing the program to continue seamlessly. A very important point worth noting! Let's review, once an interrupt is detected, it’s important to finish the current instruction before addressing it.
Introduction & Overview
Read a summary of the section's main ideas. Choose from Basic, Medium, or Detailed.
Quick Overview
Standard
This section details the key objectives of the unit, focusing on the process of instruction execution, particularly in relation to interrupts and how they affect the program counter and instruction cycles. It emphasizes the stages involved in servicing interrupts and the significance of the instruction cycle code.
Detailed
Objectives of the Unit
In this unit, we will explore the essential concepts of instruction execution, particularly focusing on the indirect phase known as interrupts. An interrupt occurs when the normal flow of code execution is interrupted by hardware or I/O devices requiring urgent attention. This section will discuss the flow of control during instruction execution, highlighting how the program counter (PC) is managed during interruptions.
The key components of interrupt handling include:
- Saving the Program Counter (PC): When an interrupt occurs, the current value of the PC must be saved, allowing the execution to resume where it left off once the interrupt has been serviced.
- Jumping to the Interrupt Service Routine (ISR): After saving the PC, the address of the ISR is loaded into the PC to handle the interrupt. This signifies a jump from the main code execution to a dedicated routine for servicing the interrupt.
- Returning from the Interrupt: Once the ISR completes its execution, the saved PC value is popped from the stack to return the execution flow to its original state.
This section concludes by emphasizing the instruction cycle stages, including fetch, decode, and execution, alongside the importance of checking for interrupts only after completing these cycles to avoid potential deadlocks.
Youtube Videos
Audio Book
Dive deep into the subject with an immersive audiobook experience.
Understanding Interrupts
Unlock Audio Book
Signup and Enroll to the course for listening the Audio Book
Now, we are coming to the indirect phase of instruction execution that is a interrupt. As we again discuss that interrupt is basically a normal flow of code is going on, then some hardware or some IO devices interrupt which has to be serviced in urgent manner then basically the instruction starts.
Detailed Explanation
An interrupt is a signal to the processor emitted by hardware or software indicating an event that needs immediate attention. It interrupts the normal execution flow, allowing the system to process other tasks or handle events quickly. For instance, when a user presses a key on a keyboard, it generates an interrupt so the CPU can process that input without delay.
Examples & Analogies
Think of a movie theater where a person is watching a film. If someone in charge of managing the show notices a fire alarm, they immediately step in (similar to an interrupt) to ensure everyone's safety, instead of waiting for everyone to finish watching the movie.
Saving the Program Counter
Unlock Audio Book
Signup and Enroll to the course for listening the Audio Book
So, after no interrupt can offer where the instruction is being executed, instruction 1 2 3 4 5 6 7 8 9 10 is going on it between no interrupt can come. But after an instruction have been executed it will check whether there is an instruction interrupt. If there is a interrupt it has come then what you do you save the value of 𝑃𝐶 in a stack.
Detailed Explanation
After executing each instruction, the processor checks for interrupts. If an interrupt occurs, the current value of the Program Counter (PC)—which holds the address of the next instruction—is saved onto a stack (a data structure that operates on a last in, first out principle). This allows the CPU to return to its previous state after servicing the interrupt.
Examples & Analogies
Imagine you're in a meeting, and your phone rings. You jot down a note of where you were in the discussion (like saving the PC) before stepping out to take the call. Once the call is over, you can return to your notes and continue from where you left off.
Interrupt Service Routine (ISR)
Unlock Audio Book
Signup and Enroll to the course for listening the Audio Book
So, what we will do? You will save the value of program counter all the registers intermediate values in a stack and then you will go to the instruction service routine who will instruction service routine nothing but another code itself or a code module with the some instruction is a jump.
Detailed Explanation
Once the PC value and other necessary registers are saved, the CPU jumps to an Interrupt Service Routine (ISR). The ISR is a function specifically designed to handle certain interrupts and perform tasks like reading data from an input device or responding to a signal. After finishing the ISR, control is returned to the main program by restoring the saved PC and registers.
Examples & Analogies
Consider a customer service approach where an employee handles customer complaints (ISR). After addressing the concern, the employee returns to their previous task, continuing from where they had stopped (the PC).
Fetching and Executing Instructions
Unlock Audio Book
Signup and Enroll to the course for listening the Audio Book
So, again the value after you complete the ISR you put pop back the value of 𝑃𝐶 from the stack, so now again 𝑃𝐶 will have the value of 10 and again you will restart everything. So, that is what is the idea of an interrupt service routine.
Detailed Explanation
After the ISR is complete, the CPU retrieves the saved PC value from the stack (this is called 'popping' the stack) and resumes executing instructions right where it was interrupted. This allows the program to continue its execution seamlessly as though the interrupt had not occurred.
Examples & Analogies
Think about a student studying for an exam who gets a text from a friend. The student takes a moment (interrupt) to respond and then goes back to the same page in their textbook where they were last studying without losing their place.
Definitions & Key Concepts
Learn essential terms and foundational ideas that form the basis of the topic.
Key Concepts
-
Instruction Execution: The method by which the CPU processes instructions.
-
Interrupt Handling: The process of managing requests that temporarily halt the normal operation of the CPU.
-
Instruction Cycle Phases: Fetch, Decode, and Execute are the three essential phases of instruction processing.
Examples & Real-Life Applications
See how the concepts apply in real-world scenarios to understand their practical implications.
Examples
-
When a keyboard is pressed, the CPU receives an interrupt, stopping the current task to process the keyboard input.
-
In a data transfer operation, when a device requests attention during a data transfer, the CPU will save the current context and service the device's needs.
Memory Aids
Use mnemonics, acronyms, or visual cues to help remember key information more easily.
🎵 Rhymes Time
-
When an interrupt rings the bell, save the PC, all will be well.
📖 Fascinating Stories
-
Imagine a busy restaurant where a waiter must pause to serve a VIP guest. The regular customers wait for their orders while the waiter takes the special order, remembering exactly where to continue afterward.
🧠 Other Memory Gems
-
F-D-E for the phases: Fetch, Decode, Execute!
🎯 Super Acronyms
ISR = Interrupt Service Routine, our CPU's helper in need!
Flash Cards
Review key concepts with flashcards.
Glossary of Terms
Review the Definitions for terms.
-
Term: Program Counter (PC)
Definition:
A register in the CPU that contains the address of the next instruction to be executed.
-
Term: Interrupt
Definition:
A signal that temporarily halts a CPU's current operations to allow the handling of an event.
-
Term: Interrupt Service Routine (ISR)
Definition:
A special block of code that handles the execution when an interrupt occurs.
-
Term: Instruction Cycle Code (ICC)
Definition:
A code that indicates the current phase of instruction execution in the CPU.
-
Term: Program Status Word (PSW)
Definition:
A register that contains the status of the processor, including condition codes and interrupt status.