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Interactive Audio Lesson
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Programmed I/O Challenges
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Today, we're going to explore how the CPU interacts with I/O devices. Can anyone tell me what happens when the CPU needs to check the status of an I/O device?
Does it just wait until the device is ready?
Exactly! This process is called polling. The CPU continually checks if the device is ready by looking at a status register. However, this leads to wasted CPU time. Can anyone explain why that's a problem?
Because while it's checking, it can't do anything else?
Correct! The CPU is idle during this waiting period, which is inefficient. We can remember this as the 'Polling Problem'. Let's summarize: polling can lead to wasted time, especially if the I/O device takes long to respond.
What are some solutions to avoid this issue?
Great question! One solution is interrupt-driven I/O. Instead of polling, the device will send an interrupt signal to the CPU when it's ready. We'll cover that in detail later.
I/O Commands and Their Functions
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Now, let's discuss the commands needed to operate I/O devices. What do you think are the basic types of commands we need?
Are there commands for reading and writing data?
Absolutely! We have read and write commands. To remember them, think of 'R' for reading in data and 'W' for writing out data. Can anyone think of other commands?
Control commands to start the operation?
Exactly! Control commands are used to initialize the devices, like waking them up or moving a printer head. Summarizing: we need read, write, and control commands for efficient I/O operations.
What about checking the device status?
Good point! We also need to send status-checking commands. Together, these commands allow the CPU to communicate effectively with I/O devices.
Addressing Schemes for I/O Devices
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Next, let's dive into addressing I/O devices. Why do we need unique addresses for each device?
To identify them separately, right?
Exactly! Each device must have a unique binary address, much like how memory addresses work. Who can tell me how these addresses are structured?
They’re a stream of bits, zeros, and ones?
Correct, each address is unique and helps the CPU locate the device. We have two methods of addressing: memory-mapped I/O and isolated I/O. What might be the difference?
Isn’t memory-mapped I/O using the same address space as memory?
That's right! Memory-mapped I/O shares its address range with memory devices, but isolated I/O uses a separate address space. This means isolated I/O can accommodate more devices. Let’s sum this up: unique addresses are essential for operation, with memory-mapped and isolated I/O as key methodologies.
Transfer Methods: Memory-Mapped vs. Isolated I/O
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Let’s delve deeper into the differences between memory-mapped and isolated I/O. Why do we prefer one over the other?
Memory-mapped I/O is simpler because it uses standard instructions, right?
Exactly! In memory-mapped I/O, you can use existing instructions for both memory and I/O operations. What about isolated I/O, though?
It has its own address spaces, allowing more devices but requires separate commands?
You got it! Isolated I/O lets us connect many devices by avoiding address space competition. Let's remember: 'M' for Memory-Mapped and 'I' for Isolated—simplifying by remembering key functionalities!
So, memory-mapped is all about simplicity, while isolated offers expansion?
Exactly! This is a crucial point to remember in understanding how we manage our hardware resources efficiently.
Introduction & Overview
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Quick Overview
Standard
The section elaborates on programmed I/O and the challenges it poses, particularly the CPU's need for constant polling that results in wasted time. It then covers the necessary commands for operating I/O devices, explains addressing schemes, and differentiates between memory-mapped I/O and isolated I/O methods.
Detailed
Detailed Summary
This section explains the fundamental aspects of managing I/O devices in computer architecture. It begins by identifying the primary function of the CPU in detecting I/O device readiness, which it does via polling, but highlights this as a source of inefficiency since the CPU is unable to perform other operations while monitoring device status. This is referred to as programmed I/O, where the CPU continuously checks the status register until the device is ready—indicated by a bit being set to '1'.
Further, the section outlines the steps involved in programmed I/O, detailing the CPU's role in issuing I/O requests, the I/O module's response, and the lack of direct interruption to the CPU.
Highlights include prerequisite commands for identifying I/O modules, controlling devices, and reading/writing data. The addressing scheme is significant, resembling memory addressing but includes unique identifiers for each I/O device.
The section contrasts two mapping methods: memory-mapped I/O, which shares address space with memory devices, allowing for a limited number of devices; and isolated I/O, providing separate address spaces for memory and I/O with potential for connecting more devices. The use of control signals, particularly the IO/M bar to distinguish between memory and I/O addresses, is discussed.
Finally, it touches upon input/output commands necessary for interaction with devices and emphasizes the importance of device service routines in executing I/O operations through software.
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Concept of Programmed I/O
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So, basically it is a sensing of status, then using the read write command, then transferring of data; this is the way that we are going to do, but here what is the problem that we have first? CPU needs to wait and poll, it is checking it continuously. So, it cannot do any other work. So, there is a wastage of CPU time.
Detailed Explanation
This chunk discusses how programmed I/O operates. It primarily involves the CPU constantly polling the I/O device to check if it's ready for data transfer. This repeated checking consumes CPU resources and prevents it from performing other tasks, leading to inefficiencies.
Examples & Analogies
Consider a busy restaurant where the waiter often visits the kitchen to check if the food is ready without receiving any notifications. This constant checking delays the waiter from attending to other customers, wasting time and resources.
Steps in Programmed I/O
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So, basically this is now programmed I/O details now you just see these are the simple steps; first one CPU requests to I/O operation that in processor we have shown it, I/O module performs operation, then by looking into the state of the devices I/O module sets the status bit, CPU checks status bits periodically, I/O module does not inform CPU directly.
Detailed Explanation
The programmed I/O process involves several steps: First, the CPU initiates the I/O operation. The I/O module executes the requested operation and updates a status bit indicating whether the device is ready. The CPU periodically checks this status bit to determine if it can proceed with data transfer. Notably, the I/O module does not automatically notify the CPU when the device is ready, adding to the polling burden on the CPU.
Examples & Analogies
Imagine a student who is waiting for the teacher to finish grading exams. The student keeps checking in to see if the teacher is done, although the teacher won’t announce completion until asked. This scenario is similar to how the CPU continuously checks the I/O module's status.
I/O Commands and Device Addressing
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Already I have mentioned that we need some commands I/O commands. So, first the issues for that I/O command is like that how to identify the module. So that means, we have to have device address so this is the one point how we are going to give the addresses of the I/O devices.
Detailed Explanation
I/O operations require specific commands for execution, particularly the means to identify each I/O device via a unique address. This addressing system ensures that the CPU can accurately communicate with and send commands to distinct devices. Thus, every device in the system must have a unique identifier similar to how every house has a unique address.
Examples & Analogies
Think of sending a letter. You must write a specific address on the envelope so that the postman knows exactly where to deliver it. Similarly, each I/O device is given a unique address to ensure commands reach the correct device.
Addressing Schemes
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So, this is the addressing scheme. So, what is the address? It is very much similar to the address of a memory location which contains 0s and 1s ok; that is all.
Detailed Explanation
The addressing scheme for I/O devices mimics that of memory addresses, represented as binary combinations of 0s and 1s. Each device address functions similarly to a memory location, giving the system a way to uniquely identify and locate devices throughout the I/O management process.
Examples & Analogies
It's akin to how different street addresses make it easy to find your friend's house. Just like each house needs a distinct address to avoid confusion, each I/O device must have a unique address for accurate support from the CPU.
I/O Mapping Techniques
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Now, in that particular case we are having two different ways of doing it. One is your memory mapped I/O and second one is your isolated I/O.
Detailed Explanation
There are two primary methods for mapping I/O devices to the CPU: memory-mapped I/O and isolated I/O. In memory-mapped I/O, both memory and I/O devices share the same address space, whereas isolated I/O maintains separate address spaces for memory and I/O devices. This distinction fundamentally changes the way the system accesses these devices and determines how many devices can be connected.
Examples & Analogies
Consider a town's zip code system as a mapping technique. If all buildings (houses and shops) share the same zip code area (memory-mapped), it's more challenging to identify exact locations. In contrast, if houses and shops have distinctly different zip codes (isolated), it becomes simpler to manage specific locations.
Control Signals in Isolated I/O
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Now how to identify whatever addresses that we have put in this particular address bus. It is an address of a memory location or it is an address of an I/O devices. So, to identify these things so, we are going to use one more control signal, there will several control signal will come through this particular control bus.
Detailed Explanation
In isolated I/O, control signals play a crucial role in differentiating between memory addresses and I/O device addresses. The CPU uses a dedicated control signal, frequently labeled as IO/M, to ascertain whether the information on the address bus pertains to a memory location or an I/O device. If the control signal indicates a memory access, the address is treated as a memory address; if it indicates I/O, the address corresponds to an I/O device.
Examples & Analogies
Imagine a security system at the entrance of a building that scans the ID badges of employees and visitors. Depending on the ID (control signal), the system determines whether the individual can enter the office areas (memory) or visitor areas (I/O devices), maintaining a clear distinction between groups.
Definitions & Key Concepts
Learn essential terms and foundational ideas that form the basis of the topic.
Key Concepts
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Polling: The process of the CPU checking the status of an I/O device.
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Programmed I/O: A method in which the CPU manages data transfers to and from I/O devices.
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Status Register: Holds information regarding the readiness of I/O devices.
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Memory-Mapped I/O: A scheme where the I/O devices share address space with memory.
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Isolated I/O: A scheme providing separate address spaces for memory and I/O devices.
Examples & Real-Life Applications
See how the concepts apply in real-world scenarios to understand their practical implications.
Examples
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When a keyboard sends data to the CPU, the CPU continuously checks the status of the keyboard (polling) until data is available for processing.
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A printer requires control commands to initialize its operation before data can be sent from the computer.
Memory Aids
Use mnemonics, acronyms, or visual cues to help remember key information more easily.
🎵 Rhymes Time
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Poll the stall, before I write, control commands bring devices to light.
📖 Fascinating Stories
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Once upon a time, a CPU was tired of waiting. It kept asking the devices, 'Are you ready now?' One day it discovered that some devices would wave flags when ready, ending the endless nagging and inefficiency forever!
🧠 Other Memory Gems
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Remember: 'PIR' - Polling, I/O Commands, and Read/Write actions to recall our I/O operations.
🎯 Super Acronyms
For I/O addressing, think 'MII'
- Memory-Mapped vs. Isolated I/O!
Flash Cards
Review key concepts with flashcards.
Glossary of Terms
Review the Definitions for terms.
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Term: CPU
Definition:
Central Processing Unit; the primary component that performs most of the processing inside a computer.
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Term: Polling
Definition:
The process by which the CPU repeatedly checks whether an I/O device is ready for data transfer.
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Term: Programmed I/O
Definition:
A method of I/O operation where the CPU actively controls the transfer of data to and from I/O devices.
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Term: I/O Module
Definition:
A hardware component that facilitates communication between the CPU and I/O devices.
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Term: MemoryMapped I/O
Definition:
An addressing scheme where I/O devices share the same address space as memory.
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Term: Isolated I/O
Definition:
An addressing scheme that uses a separate address space for I/O devices, allowing more devices to connect without address conflicts.
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Term: Control Commands
Definition:
Commands issued to initiate operations on I/O devices.
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Term: Status Register
Definition:
A register that holds the status information about I/O devices.