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Interactive Audio Lesson
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Introduction to Programmed I/O
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Today, we are going to discuss the basics of programmed I/O and its steps. Can anyone tell me what programmed I/O is?
Isn't programmed I/O where the CPU communicates with I/O devices through commands?
Exactly! In programmed I/O, the CPU issues commands to the I/O module. Let's break that down. What do you think happens after that command is issued?
The I/O module needs to check if the device is ready?
That's correct! It checks the device status, sets status bits, and the CPU then polls those bits. Why is polling a problem?
It wastes CPU time because it can't do other tasks while waiting?
Right! This waiting can lead to inefficiencies in CPU use. Now, can anyone suggest what the next step after checking the device status might be?
The CPU waits until the device is ready to perform the data transfer?
Exactly! Great job. This process continues until the data transfer is complete.
Addressing I/O Devices
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Now let's talk about how I/O devices are addressed. Who can explain why addressing is important in I/O operations?
It's important because the CPU needs to know what device it is communicating with?
Exactly! Each device must have a unique address, similar to memory addresses. Can anyone think of how these addresses are represented?
They're represented in binary, just like memory addresses?
That's right! Addresses are typically a stream of 0s and 1s. Now, can someone tell me about the difference between memory-mapped I/O and isolated I/O?
Memory-mapped I/O shares the same address space as memory, while isolated I/O has a separate space?
Perfect! In memory-mapped I/O, we can use normal memory instructions, but isolated I/O requires special instructions. Any questions on that?
Commands for I/O Devices
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Let's delve into the commands necessary for the I/O devices. There are three main categories of commands. Who can name them?
Control commands, status commands, and read/write commands?
Great memory! Can someone explain what each type of command does?
Control commands initiate actions on the device, status commands check if the device is ready, and read/write commands transfer data?
Exactly! Why do you think it's essential to have this classification of commands?
It helps organize how we interact with different devices, ensuring we send the right commands?
Spot on! Keeping commands organized helps avoid confusion during data transfer. Let's summarize what we've learned about commands.
I/O and CPU Interaction
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To wrap up, how does the interaction between the CPU and I/O devices look in programmed I/O?
The CPU initiates communication, the I/O module checks status, and data is transferred when the device is ready?
Exactly! And what are the potential drawbacks of this method?
The CPU can waste a lot of time polling the device, which isn't very efficient.
Correct! It's crucial to be aware of these inefficiencies when designing systems. Remember, effective communication between the CPU and I/O devices is essential. Any last questions?
Introduction & Overview
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Quick Overview
Standard
Programmed I/O involves several critical steps: the CPU requests an I/O operation, the I/O module sets status bits, and the CPU polls those bits to determine when data transfer can occur. This process can lead to CPU inefficiencies as it may waste time waiting for the I/O device to be ready.
Detailed
Steps in Programmed I/O
Programmed I/O is a method by which a CPU interacts with input/output devices through a sequence of specific commands. The process begins with the CPU issuing a request to the I/O module to perform an operation. The I/O module then checks the status of the device and sets the appropriate status bits indicating whether the device is ready for data transfer. Unlike interrupt-driven I/O, where the I/O module informs the CPU directly, in programmed I/O, the CPU must continuously poll the I/O module to check the status. This continuous checking can lead to inefficiencies as the CPU may waste cycles waiting.
The address of the I/O device must also be specified in the I/O command, similar to how memory addresses are provided when reading from or writing to memory. Furthermore, I/O operations can be grouped into three categories: control commands (to initiate device actions), status commands (to check device conditions), and read/write commands (to transfer data).
There are two addressing schemes for I/O devices: memory-mapped I/O, where I/O devices share the same address space as memory, and isolated I/O, which has separate address spaces for I/O and memory. This segmentation allows for a greater number of devices to be addressed. Understanding programmed I/O is crucial for recognizing how data is transferred between the CPU and I/O devices effectively.
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Overview 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
Programmed I/O involves the CPU checking the status of an I/O device before performing an action. The CPU continuously polls or checks if the device is ready, which means it's waiting for the device to signal that it is prepared for data transfer. This waiting can consume significant CPU time, leading to inefficiencies because the CPU is not free to perform other tasks while it waits.
Examples & Analogies
Imagine waiting in a queue to use a public restroom. You stand there doing nothing else while you wait for someone to finish. While you're waiting, you could be enjoying a coffee or reading a book, but instead, your time is wasted because you're preoccupied with just waiting.
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 first step in programmed I/O is when the CPU sends a request to an I/O device to perform an operation. The I/O module then carries out the operation and checks the state of the device. Once the operation is done, the I/O module sets a status bit to indicate the status of the device (e.g., whether it is ready for the next operation). The CPU then checks the status bit at intervals to see if the operation can proceed. Unlike interrupt-driven I/O, the I/O module does not alert the CPU directly; it simply waits for the CPU to check the status.
Examples & Analogies
Think of this like ordering a pizza. You call the restaurant (CPU requesting I/O) and place your order. The restaurant staff (I/O module) processes your order and puts the pizza in the oven. Until the pizza is done, you keep checking your watch (CPU checking status bits) to see if it's time to pick it up. The restaurant doesn’t call you to say your pizza is ready; instead, you have to keep checking.
Device Addressing and Command Issuance
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I/O command issues like how to identify the module, we have to have device address, so this is one point how we are going to give the addresses of the I/O devices.
Detailed Explanation
To perform I/O operations, the CPU must identify which device it is communicating with. This requires a device address unique to each I/O device. The device address allows the CPU to specify which device to read from or write to. Just like memory addresses, device addresses are also represented in binary, allowing for effective identification and communication between the CPU and the I/O devices.
Examples & Analogies
Consider a multi-student classroom where each student has a unique seat number. When the teacher wants to call on a specific student, they refer to the seat number. In the same way, the CPU uses the unique device address to select which I/O device it wants to communicate with.
Control Commands for I/O Devices
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Basic requirements to perform work with the I/O module or input-output devices involve control commands to initiate processes such as sending control signals to the printer.
Detailed Explanation
Control commands are essential for facilitating operations with I/O devices. These commands allow the CPU to send instructions to the devices—for instance, to initiate printing or to set the position of a disk head when reading from a hard drive. These commands not only initiate actions but may also check the power status or readiness of the device, ensuring the proper workflow.
Examples & Analogies
Think of the control commands as the instructions given to a chef in a kitchen. Just like a chef needs specific commands to prepare a dish (such as 'chop the vegetables' or 'preheat the oven'), I/O devices require commands so they can perform their tasks effectively.
Modes of Data Transfer: Read and Write
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The mode of transfer is basically read, which means we are taking something from the input device, and write, which means we are putting some information into the output device.
Detailed Explanation
Data transfer can be categorized into two primary modes—read and write. In the read mode, information is retrieved from an input device to be processed by the CPU. In the write mode, data processed by the CPU is sent to an output device. This dual functionality is crucial for data exchange and communication between the CPU and I/O devices, ensuring that data flows seamlessly both in and out.
Examples & Analogies
Picture a library where you can both borrow books (read) and return them (write). When you borrow a book, you are taking it out from the library's collection. When you return it, you are putting it back into the library. The library’s system manages both actions, just like how the CPU manages both reading from and writing to I/O devices.
Memory-Mapped I/O and Isolated I/O
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We are having memory mapped I/O and isolated I/O, and I will just simply explain it with the help of a small example.
Detailed Explanation
There are two main methods of mapping I/O devices in relation to memory: memory-mapped I/O and isolated I/O. In memory-mapped I/O, the same address space is shared by both memory and I/O devices, allowing for simpler commands to operate with both. Conversely, in isolated I/O, the memory and I/O spaces are distinct, requiring additional control signals to differentiate between memory and I/O device addresses.
Examples & Analogies
Think of memory-mapped I/O as using a single shopping cart in a grocery store. You can pick up items from different sections (like fresh produce or household goods) in one go. In contrast, isolated I/O is like needing two separate carts for grocery shopping and clothes shopping. You could navigate through different parts of the mall but would need to switch between carts and perhaps even pay for items separately.
Transfer Control via Control Signals
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To identify whether an address is for memory or an I/O device, we need a control signal, typically referred to as the IO/M signal.
Detailed Explanation
The IO/M control signal is crucial in an isolated I/O system; it helps the CPU determine whether the address currently being addressed is for a memory location or an I/O device. If the IO/M signal is 0, the address is treated as a memory address. If it is 1, the address refers to an I/O device. This distinction is essential for effective data transfer and functionality.
Examples & Analogies
Consider a traffic light at an intersection with different signals. When the light is green, cars can go (indicating a memory address). When the light is red, cars must stop and wait (indicating an I/O address). The light's colors help drivers understand when it is appropriate to move forward and when they need to halt, similar to how the IO/M signal guides the CPU in its operations.
Definitions & Key Concepts
Learn essential terms and foundational ideas that form the basis of the topic.
Key Concepts
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Programmed I/O: A method where the CPU explicitly manages data transfers with I/O devices.
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Polling: A method where the CPU repeatedly checks device status, which can lead to inefficiencies.
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I/O Module Functions: Manages communication between the CPU and peripheral devices.
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Addressing Schemes: Memory-mapped and isolated I/O define how devices are referenced in the address space.
Examples & Real-Life Applications
See how the concepts apply in real-world scenarios to understand their practical implications.
Examples
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When the CPU wants to read data from a keyboard, it sends a command to the I/O module. The module checks the keyboard's status and then transfers data once it is ready.
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In a memory-mapped I/O system, the command to send data to a printer could use the same assembly instruction as a command to access memory since both share the same address space.
Memory Aids
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🎵 Rhymes Time
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Polling for a device, checking its status with grace, waiting for readiness in our CPU race.
📖 Fascinating Stories
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Imagine a busy office where the manager must check if each worker is ready to provide reports, one by one, instead of getting a bell to ring when they are ready. This is how programmed I/O polices its devices.
🧠 Other Memory Gems
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Remember 'PCR' for programmed I/O: P for Polling, C for Commands, and R for Read/Write operations.
🎯 Super Acronyms
MAPI
- Memory-mapped Addressing Protocol for I/O keeps devices and memory in the same map
- but isolated I/O has its space apart.
Flash Cards
Review key concepts with flashcards.
Glossary of Terms
Review the Definitions for terms.
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Term: Programmed I/O
Definition:
A method of data exchange between the CPU and I/O devices where the CPU actively manages the communication through polling.
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Term: Poll
Definition:
The process where the CPU checks the status of an I/O device regularly to determine its readiness for communication.
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Term: I/O Module
Definition:
A component that interfaces between the CPU and I/O devices, managing requests and communicating with peripheral devices.
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Term: Status Bit
Definition:
A binary flag set by the I/O module to indicate the state of an I/O device, such as ready or busy.
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Term: Memorymapped I/O
Definition:
An addressing scheme where I/O devices share the same address space as the main memory.
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Term: Isolated I/O
Definition:
An addressing scheme where I/O devices have a separate and distinct address space from memory.
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Term: Control Commands
Definition:
Commands used to initiate operations on I/O devices.
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Term: Read/Write Commands
Definition:
Commands that perform data transfers to or from I/O devices.