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Interactive Audio Lesson
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I/O Polling and Programmed I/O
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Let's discuss how the CPU interacts with I/O devices, specifically through a method known as polling. Polling is the process where the CPU continuously checks the status of an I/O device. Can anyone share what they think might be a downside to this method?
It sounds like it could waste a lot of time, since the CPU can't do anything else while it’s waiting!
Exactly! This wastage of CPU time can severely hinder performance. That's why we use programmed I/O as a way to manage device interactions more efficiently. Can anyone tell me what programmed I/O entails?
Isn't it when the CPU issues commands to the I/O device and then checks for certain status signals?
Great point! The CPU sends commands and must check the status bit of the device to see if it’s ready for data transfer. This leads us to the relationship between I/O modules and the CPU. Why do you think the I/O module doesn't just signal the CPU directly when it's ready?
Maybe it’s because if it interrupted the CPU, it could disrupt whatever the CPU is doing at that moment?
That's correct! By not interrupting, the CPU can manage tasks more effectively, even if that means occasionally checking back in. So remember, polling can help us manage this, but it's not the most efficient method. Let’s summarize this concept: I/O polling is when the CPU actively checks for device readiness, which can waste time and computational resources.
Addressing I/O Devices
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Another important aspect of I/O operations is how we address these devices. Why do we need a unique address for each I/O device?
To ensure the CPU can correctly send commands to the right device!
Exactly! Without unique addressing, there would be confusion about which device is being referenced. Now, can anyone explain the difference between memory-mapped I/O and isolated I/O?
Memory-mapped I/O shares the same address space as memory, right? So I/O devices are treated like memory locations.
Correct! And what about isolated I/O? How does it work?
In isolated I/O, we have separate address spaces for memory and I/O devices, which allows more devices to be addressed overall!
Nail on the head! Using isolated I/O allows greater scalability. At the end of this discussion, remember that addressing schemes are fundamental for identifying unique I/O devices, ensuring commands go to the correct outputs.
Commands in I/O Operations
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Now that we understand the addressing part, let’s look at the types of commands needed to operate I/O devices. Can anyone name the categories of these commands?
There are control commands, test commands, and read/write commands!
Exactly! Control commands initiate processes, test commands check device statuses, while read/write commands let the CPU transfer data to and from I/O devices. How might we use these commands when programming?
You’d need to send a control command to start the operation, then continuously check the status with test commands until it’s ready to read or write data.
Perfectly articulated! Let's wrap up this session: I/O commands are categorized into control, test, and read/write, each serving crucial roles in managing device operations efficiently.
Device Service Routine and Programmed I/O
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Finally, let’s explore how we can automate the I/O process. What do we mean by a device service routine in the context of programmed I/O?
I think it's a program that can repeatedly check the status of an I/O device until it's ready before performing the actual data transfer.
Exactly! The device service routine continuously polls the device's status bits, ensuring the CPU does not waste cycles waiting. Does anyone have an idea how we could structure such a routine?
It would probably be in a loop that checks the status until it finds the device is ready, right?
Spot on! This kind of routine improves efficiency by ensuring we use CPU time effectively by waiting actively yet independently. Summarizing today’s lesson – device service routines are programmed sequences that aid in efficiently managing data transfers between the CPU and I/O devices.
Introduction & Overview
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Quick Overview
Standard
The section discusses the issues associated with Input/Output (I/O) commands, including the inefficiencies of polling for device statuses by the CPU. It details the steps of programmed I/O operations and the importance of addressing schemes for I/O devices, including concepts like memory-mapped and isolated I/O, concluding with a consideration of commands required for effective I/O operations.
Detailed
In this section, we explore the challenges of Input/Output (I/O) command handling in computer systems, particularly focusing on the inefficiencies that arise when the Central Processing Unit (CPU) continuously polls I/O devices for status updates. This repeated checking leads to wasted CPU cycles and reduced overall system efficiency.
The discussion follows through the basic steps involved in programmed I/O. When a CPU requests an I/O operation, the I/O module does not directly alert the CPU once the device is ready; instead, the CPU must periodically check the status bits of the I/O module. This fundamental setup is critical in understanding the role of I/O modules and how they interact with the CPU without direct notification via interrupts.
Additionally, we cover addressing schemes that determine how I/O devices are identified. It is necessary to assign unique addresses to the devices, similar to memory addressing, and we differentiate between two primary methods of I/O mapping: memory-mapped I/O and isolated I/O. In memory-mapped I/O, the same address space is shared for both memory and I/O devices, while isolated I/O maintains separate address spaces for each.
The commands required for controlling I/O devices are categorized into three groups: control, test, and read/write commands. Each of these categories plays a significant role in ensuring the correct operation of I/O functionalities, highlighting the need for robust command design within a processor’s instruction set. This understanding ultimately underpins effective programmed I/O techniques, showing how a device service routine can be designed to optimize these operations.
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Audio Book
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Overview of I/O Command Issues
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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
When performing input/output operations, the CPU must constantly check (or 'poll') the status of the device. This means that while it waits for the device to be ready, it is unable to perform any other tasks, leading to wasted processing time. This inefficiency highlights a major drawback of traditional programmed I/O, where the CPU is actively involved in the data transfer process.
Examples & Analogies
Imagine a student waiting for their turn to use a computer in a library. Instead of working on their own assignments, they're just sitting there, checking the clock every few seconds to see when the computer will be free. This waiting prevents them from being productive, similar to how the CPU wastes time polling I/O devices.
Programmed I/O Steps
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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.
Detailed Explanation
In programmed I/O, the process begins when the CPU makes a request for I/O operations. The I/O module then performs the necessary action based on the current state of the devices, which updates a status bit. The CPU continuously checks this status bit to determine when it can proceed with data transfer. Crucially, the I/O module does not directly notify the CPU of changes.
Examples & Analogies
Think of this like a waiter at a restaurant. The customer (CPU) places an order (I/O request), and the waiter (I/O module) goes off to see if the meal is ready. The customer keeps glancing at the kitchen (checking the status bit) to see if the meal is prepared, rather than being informed by the waiter.
I/O Command Requirements
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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
To manage I/O operations, specific commands are required. First, the CPU needs a way to identify each device by assigning a unique address to it. This address allows the CPU to communicate effectively with the appropriate device, similar to how different offices in a building have unique addresses for mail delivery.
Examples & Analogies
Consider how you send a letter. Each house has a unique address, ensuring your letter reaches the right destination. Likewise, in computer systems, each I/O device must have a unique identifier so that the system can correctly route commands and data.
Control Commands and Their Functions
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So, basically, some control commands we have to issue just to initiate the process like that already have explained. If we want to print something in the printer we should send some control signal to the printer to initiate it or maybe to bring the printer head to the appropriate position.
Detailed Explanation
Control commands are essential as they direct devices to perform specific tasks. For example, to print a document, the CPU must send commands to the printer to start the printing process and position the printer head correctly. These commands ensure that devices operate properly during their respective tasks.
Examples & Analogies
This is akin to a director giving instructions on a movie set. The director (CPU) tells the actors (I/O devices) what to do—like when to start acting or where to stand—ensuring that the production runs smoothly without confusion.
Addressing I/O Devices
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In that particular case, it is basically now, already I said that we have to give a unique identification to the processor or to the devices. So, for that we have to give an address.
Detailed Explanation
Each I/O device must have a unique address that the CPU uses for communication. This is similar to how each house has a distinct postal address to receive mail. If two devices had the same address, the CPU would not know which one to communicate with, leading to confusion and errors.
Examples & Analogies
Imagine if two friends had the same name in a group chat. If you wanted to message one of them but didn't specify which one, your message could end up confusing everyone. In computing, unique addresses prevent such miscommunication between devices.
Mapping I/O Devices: Memory-Mapped vs. Isolated I/O
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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 approaches to map I/O devices: memory-mapped I/O and isolated I/O. In memory-mapped I/O, I/O devices share the same address space as memory, allowing the use of regular memory instructions for I/O operations. In contrast, isolated I/O has separate address spaces for memory and I/O devices, requiring specific instructions to access I/O devices.
Examples & Analogies
Think of a shopping mall (memory-mapped I/O) where stores (I/O devices) and parking lots (memory) are all mixed together. You can easily access both by walking around the mall. Now, consider a city layout (isolated I/O) where residential areas (memory) and commercial areas (I/O devices) are separate. You must know if you're going to the store or your home, and you can't access one directly from the other.
Control Signals in Isolated I/O
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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, a control signal helps differentiate between memory addresses and I/O addresses. This signal indicates whether the address on the bus points to memory or an I/O device. If the control signal indicates I/O, the CPU reads from or writes to an I/O device; otherwise, it processes the memory address.
Examples & Analogies
Imagine a doorbell that signals whether a visitor is here to deliver a package (I/O) or a friend arriving for a visit (memory). The control signal acts like this doorbell, helping you determine how to respond based on who is at the door.
I/O Commands and Their Execution
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So, that's why we are saying that some special I/O command. So, these are the I/O commands that what we are having in most of the cases we can get like that; one command is your 𝑖𝑛, another command is your 𝑜𝑢𝑡.
Detailed Explanation
I/O operations utilize specific commands, such as 'in' to read data from an I/O device and 'out' to send data to one. These commands specify which device to communicate with and direct the CPU on how to handle data transfers.
Examples & Analogies
Consider these commands like specific phrases used in a diner – 'order up!' signals the kitchen (I/O devices) to send out food (data), while 'check, please!' tells the server to bring the bill. Each phrase instructs specific actions to be taken.
Device Service Routine
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So, with the help of one simple program and we are doing it which is known as your device service routine in it is basically to control that particular device, we need a program.
Detailed Explanation
The device service routine is a program that executes the sequence of steps needed to manage I/O operations. It continuously monitors the status of devices until they are ready for data transfer and then performs the necessary operations. This routine automates the management of I/O devices within the CPU's processing flow.
Examples & Analogies
Think of a conductor managing a symphony orchestra. The conductor cues each musician when to play (the device's readiness) and orchestrates the overall performance. The routine ensures that every part is coordinated, just like the device service routine manages I/O tasks.
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 I/O device readiness.
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Programmed I/O: A technique where the CPU manages I/O without interrupts.
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Status Bits: Indicators used to ascertain device readiness.
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Addressing Schemes: The methods used to assign unique IDs to I/O devices.
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Memory-Mapped I/O: A scheme where I/O and memory share the same address space.
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Isolated I/O: A method with separate address spaces for I/O and memory.
Examples & Real-Life Applications
See how the concepts apply in real-world scenarios to understand their practical implications.
Examples
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When using a printer, the CPU sends a command to start printing. The status of the printer is then polled until it is ready to print.
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In a memory-mapped I/O scenario, a CPU read instruction directed at an I/O device can use the same addressing scheme as it does for RAM.
Memory Aids
Use mnemonics, acronyms, or visual cues to help remember key information more easily.
🎵 Rhymes Time
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When you need device to respond, check its status like a pond!
📖 Fascinating Stories
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Imagine a teacher checking each student’s readiness before starting the class; this ensures no one is left behind, just like the CPU polling each I/O device!
🧠 Other Memory Gems
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Remember CRIT: Control, Read, Interrupt, Test - the types of commands used in I/O.
🎯 Super Acronyms
MISO for understanding the components
- M: for Memory-mapped
- I: for Isolated
- S: for Status
- O: for Operations.
Flash Cards
Review key concepts with flashcards.
Glossary of Terms
Review the Definitions for terms.
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Term: Polling
Definition:
The act of continuously checking the status of an I/O device to see if it is ready for data transfer.
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Term: Programmed I/O
Definition:
A method of I/O operation where the CPU issues commands and checks for device readiness.
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Term: Status Bit
Definition:
A signal that indicates the readiness of an I/O device to perform data transfer.
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Term: MemoryMapped I/O
Definition:
A method of interfacing I/O devices that uses the same address space as memory.
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Term: Isolated I/O
Definition:
A method of interfacing I/O devices with a separate address space distinct from memory addresses.
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Term: Device Service Routine
Definition:
A program that continuously checks the status of an I/O device and manages data transfers when ready.
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Term: Control Commands
Definition:
Commands that initiate operations on I/O devices.
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Term: Read/Write Commands
Definition:
Commands that facilitate the transfer of data to and from I/O devices.
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Term: Addressing Scheme
Definition:
A systematic way in which each I/O device is assigned a unique address for identification.