Questions Addressing Objectives
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Introduction to Programmed I/O
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Today, we're diving into programmed I/O. Can anyone tell me what programmed I/O entails?
I think it’s where the CPU checks the status of the I/O device repeatedly?
Exactly, that’s known as polling. It allows the CPU to monitor the state of the device, but what’s the downside?
It wastes CPU time because it can't do anything else while waiting.
Correct! This inefficiency is a key concern in system design. We need a better way to manage how devices communicate with the CPU.
Remember the mnemonic 'POW' — Polling, Output, Wait! It can help recall the primary issues with programmed I/O.
So, polling isn’t the best method because it consumes resources inefficiently.
Exactly! Understanding this sets the stage for exploring I/O modules and their roles.
I/O Addressing Schemes
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Next, let’s look into how we address I/O devices. Why do we need an addressing scheme?
To ensure that the CPU knows which device it is communicating with?
Correct! Without unique addresses, we wouldn’t be able to identify each device. Can anyone explain the difference between memory-mapped I/O and isolated I/O?
In memory-mapped I/O, the device uses the same address space as memory. But in isolated I/O, they have separate address spaces.
Great job! This distinction is crucial. Memory-mapped I/O can lead to fewer instructions needed, while isolated I/O can handle more devices.
Try to remember 'MIM' for Memory-Mapped I/O: Devices Inline with Memory. It helps visualize their connectivity.
So, more devices can be connected using isolated I/O, which is an advantage for larger systems?
Exactly! Nice connection!
Steps in I/O Operations
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Let’s move on to the steps in I/O operations. Can anyone outline what happens during an I/O instruction?
The CPU first sends a request for the I/O operation.
Correct! Then what happens?
The I/O module performs the operation and sets the status bit.
Exactly! And then the CPU checks these status bits. What else can happen after this?
If it’s ready, the CPU can start transferring data?
Right! Remember: 'Request, Report, Respond.' It outlines the flow. This summarizes the key actions during I/O operations.
So, these steps ensure that the communication is synchronized!
Exactly! That synchronization is vital for effective device communication!
I/O Commands and their Functions
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Now, let’s discuss I/O commands. What types of commands do you think are necessary for I/O operations?
Control commands to start the operation and check the device status.
Exactly! We also need read and write commands, correct?
Yes! Those specify what data we are getting or sending.
Correct! Remember the acronym 'RWC' for Read, Write, Control. It can help you remember the types of commands.
So, these commands are essential for ensuring proper communication with I/O devices?
Absolutely! Without them, we couldn’t control or transfer data effectively.
Introduction & Overview
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Quick Overview
Standard
In this section, we explore the procedure for programmed I/O, including its inefficiencies, the necessity for I/O modules, addressing schemes, and the distinction between memory-mapped and isolated I/O. Detailed steps for I/O operations are also elucidated.
Detailed
Detailed Summary
This section elucidates the mechanics of programmed I/O, where a CPU continuously polls an I/O device to check its status. This approach results in inefficient CPU time as it cannot perform other tasks while waiting. The chapter highlights the need for an addressing scheme to clearly identify input/output devices, similar to memory addresses but uniquely assigned to each device.
It further distinguishes between memory-mapped I/O, where I/O devices share the same address space as memory, and isolated I/O, where separate address spaces exist for memory and I/O devices. The section summarizes the steps in I/O operations: the CPU requests I/O operations, the I/O module performs its tasks, sets status bits, and checks for completion. Lastly, it discusses the essential commands for I/O operations, including read and write commands, emphasizing that efficient data transfer relies on the structured addressing and command system.
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Overview of Programmed I/O
Chapter 1 of 6
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Chapter Content
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
In programmed I/O, the CPU checks the status of the I/O device continuously (this is called polling). While doing this, the CPU cannot perform other tasks, which leads to wasted time and efficiency reduction. Polling involves the CPU sending requests to the I/O device to see if it is ready for data transfer, which can delay the completion of other processes.
Examples & Analogies
Imagine a worker (the CPU) constantly checking if a printer (the I/O device) is ready to print. While waiting, the worker cannot start other tasks, such as preparing the next report. This wasted waiting time can be very inefficient, just like how the CPU waits instead of doing useful work.
Steps in Programmed I/O
Chapter 2 of 6
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Chapter Content
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, you now see that here I/O module is not going to inform the CPU directly that device is ready, but in case of interrupt driven in somewhere, in somewhere I/O module is going to inform this particular things to the processor.
Detailed Explanation
The steps in programmed I/O are as follows: First, the CPU requests an I/O operation. Next, the I/O module performs the requested operation. Then, the I/O module updates a status bit to indicate whether the device is ready. The CPU periodically checks this status bit to see if it can proceed. In programmed I/O, the I/O module does not directly notify the CPU, unlike in interrupt-driven I/O systems where the module informs the CPU immediately.
Examples & Analogies
Think of this process like a restaurant (CPU) that provides a menu (I/O operation request) to a waiter (I/O module). The waiter goes to the kitchen (the I/O module) to prepare the food. The waiter must keep checking back to see if the food is ready (status bit update) but does not tell the restaurant right away when it is ready. Instead, it waits until the restaurant checks back periodically.
Addressing I/O Devices
Chapter 3 of 6
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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 communicate with I/O devices, the CPU needs to identify them using unique device addresses. This is similar to how each house on a street has a distinct address so that mail can be delivered correctly. Each I/O device must have a specific identifier so that the CPU can accurately send commands to the right device.
Examples & Analogies
Consider a post office that must deliver mail to various neighborhoods. Each house (I/O device) has a unique address. If a letter is sent without a correct address (device address), it might end up at the wrong house. Similarly, the CPU ensures commands are sent to the correct I/O device by using specific addresses.
Control Commands
Chapter 4 of 6
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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 necessary instructions sent from the CPU to the I/O devices to initiate actions. For example, before printing, the CPU must send a command that tells the printer to start preparing itself. These commands ensure that the I/O devices are ready to perform their functions before any data transfer takes place.
Examples & Analogies
Imagine a conductor of an orchestra (the CPU) signaling musicians (I/O devices) to get ready before the performance. The conductor raises a baton (control command) to prepare the musicians to start playing. If the musicians don’t receive this signal, they won’t know when to begin.
I/O Mapping Techniques
Chapter 5 of 6
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Now how we are going to give this particular address, how we are going to map this particular input output devices. So, for that we have to look I/O mapping, so how we are going to map the I/O devices to the processor. So, that we can identify that particular device correctly.
Detailed Explanation
I/O mapping techniques are strategies used to assign unique addresses to different I/O devices, allowing the CPU to interact effectively with them. There are two primary methods: memory-mapped I/O where I/O devices are assigned addresses within the memory space, and isolated I/O where devices have a dedicated addressing space, making it easier to differentiate between memory and I/O addresses.
Examples & Analogies
Consider a city divided into two distinct areas: one for residential buildings (memory space) and another for businesses (I/O space). The city planner (CPU) must know where to find homes and where to find stores. In memory-mapped I/O, homes and stores share the same avenue; in isolated I/O, they have their separate streets. This organization helps the planner efficiently access both types of properties.
Conclusion and Summation of Objectives
Chapter 6 of 6
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Chapter Content
So, these are the issues, basically we have one is your addressing scheme, second one is what are the commands that we need to handle this particular input output devices and along with that I think we have already used those particular program I/O details.
Detailed Explanation
In conclusion, effective I/O operations hinge on understanding the addressing scheme for devices, the commands required to communicate with them, and the programming involved in programmed I/O. Each aspect is vital to ensure smooth interaction between the CPU and external devices, thus fulfilling the objectives laid out for the unit.
Examples & Analogies
Think of a successful team project: a clear communication plan (addressing scheme), assigned roles (commands), and a project timeline (programming details) are necessary for success. Just like these pieces work together for a team, addressing, commands, and programming are essential for successful I/O operations.
Key Concepts
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Programmed I/O: A CPU-controlled method of managing input and output operations requiring continuous polling.
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Polling: The regular checking of I/O device status, often leading to inefficiencies in CPU usage.
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Memory-Mapped I/O: An architecture that integrates I/O device addressing within the memory address space.
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Isolated I/O: A distinct addressing scheme providing separate address spaces for I/O devices to enhance device management.
Examples & Applications
When the CPU reads a value from a keyboard, it polls the keyboard to check for user input continuously.
In memory-mapped I/O, using an address such as 0x0001 might refer to both a memory location and an I/O device.
Memory Aids
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Rhymes
When the CPU must poll and check, it wastes its time with no respect.
Stories
Imagine a doctor waiting on a patient to describe their ailment. While waiting, the doctor cannot treat other patients. This is like a CPU waiting on an I/O device.
Memory Tools
Remember 'CRISP' for I/O commands: Control, Read, Input, Send, Process!
Acronyms
Use 'PIM' to remember Programmed I/O, Isolated I/O, Memory-mapped I/O.
Flash Cards
Glossary
- Programmed I/O
A method where the CPU continuously polls an I/O device until it becomes ready for data transfer.
- Polling
The process of the CPU checking the status of an I/O device at regular intervals.
- MemoryMapped I/O
An addressing scheme where I/O devices share the same address space as memory locations.
- Isolated I/O
An addressing scheme where I/O devices have separate address spaces from memory, allowing for distinguishing device types.
- I/O Module
A component that manages the communication between the CPU and I/O devices, including status checking and command execution.
Reference links
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