Execution of Device Service Routine
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Introduction to Programmed I/O
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Today we'll explore how the CPU interacts with I/O devices using programmed I/O. Can someone explain what programmed I/O means?
I think it means the CPU sends commands to the I/O devices directly.
Exactly! In programmed I/O, the CPU actively controls the communication. However, what is a downside of this approach?
The CPU has to wait and keep checking the device status, which wastes time.
Great point! That's why we need efficient routines or programs, known as device service routines, to manage these communications effectively.
So, it’s like a check-list for the CPU to follow before it communicates with an I/O device?
Exactly! The device service routine acts like a guide for the CPU in polling and executing I/O tasks.
Steps in I/O Operation
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Let’s break down the steps involved in an I/O operation. Can anyone list the first step of a programmed I/O system?
The CPU requests the I/O operation.
Correct! What comes next?
The I/O module performs the operation and checks the device status.
Good observation! Next, the CPU checks the status bit periodically. Why do we do this?
To find out if the device is ready to transfer data!
Exactly! If the status indicates it's ready, the CPU can proceed with the data transfer, ensuring an efficient I/O operation.
Addressing I/O devices
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Now let's talk about addressing I/O devices. Why is device addressing essential?
So the CPU can identify which device it wants to communicate with?
Correct! Addressing is crucial. Can anyone tell me the difference between memory-mapped I/O and isolated I/O?
In memory-mapped I/O, both memory and I/O use the same address space, but in isolated I/O, they have separate spaces.
Exactly! And how does that impact data transfer?
With memory-mapped, we can use normal memory instructions, but with isolated I/O, we need special commands.
Well explained! The right understanding of addressing mechanisms ensures efficient CPU-I/O interactions.
Commands for I/O operations
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Let's look at the types of commands required for I/O operations. What types can we identify?
Control commands, read commands, and write commands.
Great job! Can someone provide examples of control commands?
Like when we need to start or reset a printer.
Exactly! You would send commands to initialize devices. Knowing these commands aids effective device management.
So, without these commands, the devices wouldn't know what to do?
Precisely! Commands are the language the CPU uses to communicate with I/O devices.
Conclusion and Review
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Let’s summarize what we've learned about device service routines and programmed I/O. Can someone describe the essence of programmed I/O?
It’s a method where the CPU controls I/O operations by checking device statuses.
Correct. What are the necessary steps involved?
1) Request an I/O operation, 2) Check status, 3) Transfer data.
Excellent! And finally, what is the identification system for devices?
I/O devices have unique addresses, and there are two mapping strategies: memory-mapped and isolated.
Well articulated! Remember, a robust understanding of these concepts is vital for efficient system operations.
Introduction & Overview
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Quick Overview
Standard
This section elaborates on the execution of device service routines, outlining the significance of programmed I/O in addressing I/O operations. Key concepts include the status checking of I/O devices, commands for data transfer, addressing schemes, and the distinction between memory-mapped and isolated I/O.
Detailed
Execution of Device Service Routine
This section covers the execution of device service routines pivotal in programmed I/O operations. The CPU frequently polls I/O devices, checking their status through a program loop. When an I/O device is ready, indicated by a status bit, data transfer is initiated. This mechanism avoids the CPU waiting idly, reducing wastage of CPU time.
Key Steps of Programmed I/O
- CPU Requests I/O Operation: The CPU initiates communication with the I/O module.
- Device Status Checking: The CPU checks the status of the devices through polling without direct interrupts from the I/O module.
- Data Transfer Process: Upon the device indicating readiness, data transfer occurs via read/write commands.
Addressing I/O Devices
An I/O device requires a unique address within the system, similar to memory addressing, to ensure proper identification and communication. Addressing schemes can be categorized into:
- Memory-Mapped I/O: Shares address space with the main memory, allowing memory operations to also function for I/O devices.
- Isolated I/O: Provides separate address spaces for memory and I/O, requiring additional control signals to differentiate between memory and I/O addresses.
Key commands include control commands, test commands, and read/write instructions necessary for the execution of these operations.
This chapter also introduces a device service routine, a specialized program used to efficiently manage and execute I/O operations, ensuring the system can handle incoming and outgoing data effectively.
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Introduction to Programmed I/O
Chapter 1 of 8
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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
This chunk introduces the concept of Programmed Input/Output (I/O). The CPU checks the status of a device by continuously polling it to see if it is ready for data transfer. This polling creates a delay because the CPU is occupied with checking the device status and cannot perform other tasks. As a result, this leads to inefficiency since CPU time is wasted while waiting for the device to become available for data transfer.
Examples & Analogies
Think of the CPU like a person trying to talk to a friend who is busy on a phone call. Instead of doing other things, this person keeps trying to get their attention by shouting their name. This waiting creates unnecessary stress and wasted time, much like the CPU waiting for the I/O device.
Steps in Programmed I/O
Chapter 2 of 8
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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.
Detailed Explanation
This chunk explains the steps involved in programmed I/O. First, the CPU issues a request for an I/O operation. The I/O module then performs the requested operation, checking the state of the device and setting a status bit to indicate whether the device is ready. The CPU periodically checks these status bits to determine if it can proceed with the data transfer. This illustrates the cyclical nature of the process, where the CPU and I/O module are in constant communication through status checking.
Examples & Analogies
This is similar to a waiter in a restaurant checking on food orders. The waiter first asks the kitchen if the meal is ready (CPU requesting operation). The kitchen then cooks the meal and indicates when it is ready (setting the status), and the waiter keeps checking back to see if the food can be served (CPU checking status).
Control Commands for I/O Devices
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So, 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.
Detailed Explanation
In this chunk, control commands necessary for I/O operations are discussed. The first task is to identify which I/O module the CPU will interact with, necessitating a device address. This address is akin to a home address for postal delivery, ensuring that data reaches the correct device.
Examples & Analogies
Imagine you are sending a birthday gift. You need the recipient's home address to ensure the package gets to the right location. Similarly, in computing, the CPU needs the specific address of the I/O module to send and retrieve data correctly.
Mode of Transfer
Chapter 4 of 8
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One is this is the mode of transfer, whether read basically we say that we are taking something from the input device and write we are saying that we are going to put some information into the output device.
Detailed Explanation
This chunk delves into the modes of transfer during I/O operations. There are generally two modes: 'read' and 'write'. In the read mode, the system fetches data from input devices, while in write mode, it sends data to output devices. Understanding these modes is crucial as they dictate how data flows between devices and the CPU.
Examples & Analogies
Consider a library where you 'read' books (checking them out) and 'write' new entries in the library record (donating books). The modes of transfer in computing work similarly, directing data flow in and out of storage.
Addressing I/O Devices
Chapter 5 of 8
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So, basically, 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
In this chunk, the addressing scheme of I/O devices is explained. Each I/O device is assigned a unique address, similar to memory locations. This unique address ensures that the CPU can access and communicate with the correct device without confusion.
Examples & Analogies
Imagine each device in a city (like traffic lights, fire stations, hospitals) has a unique address. If you want to send a message to the fire station, you need to know its specific address. In a computer, unique addresses for I/O devices serve the same purpose, directing commands precisely.
I/O Mapping Techniques
Chapter 6 of 8
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So, 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
This chunk introduces two techniques for mapping I/O devices to CPU memory: memory-mapped I/O and isolated I/O. In memory-mapped I/O, both memory and I/O devices share the same address space, limiting the number of devices that can be connected. In isolated I/O, separate address spaces are used for memory and I/O, allowing for a larger number of devices to connect to the CPU.
Examples & Analogies
Think of a college campus. In a combined campus, classrooms and offices share the same building (memory-mapped I/O), but in segregated campuses, classrooms are in one building and offices in another (isolated I/O). This separation in isolated I/O allows for more offices to be accommodated without confusion.
Connecting with Control Signals
Chapter 7 of 8
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Chapter Content
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.
Detailed Explanation
This chunk explains the importance of control signals in distinguishing between memory and I/O addresses. A specific control signal, IO/M̅, is used to determine whether the address on the address bus refers to a memory location or to an I/O device. This differentiation is crucial for correct data operation.
Examples & Analogies
It's like a reception desk in a large hotel that sorts visitors based on whether they are guests (memory) or delivery personnel (I/O devices). The reception uses specific signals (like guest cards) to direct each visitor to the appropriate location.
Conclusion of Device Service Routine
Chapter 8 of 8
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Chapter Content
So, this is the way we are going to transfer information in programmed I/O and for that we need the addressing of the devices and we need the command.
Detailed Explanation
The final chunk summarizes how information transfer occurs in programmed I/O. It emphasizes the necessity of correctly addressing devices and issuing commands to facilitate successfulcommunication between the CPU and I/O devices. This systematic approach ensures efficient operation of data transfers.
Examples & Analogies
Consider a chef who uses a recipe book to prepare meals. The recipes are like the commands, guiding the chef (CPU) on what ingredients (data) to use, and the kitchen (I/O devices) is where everything comes together. The chef must follow the correct recipe (commands) and know where to find ingredients (addresses) for successful meal preparation (data transfer).
Key Concepts
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Poll Status: The CPU continuously checks if an I/O device is ready for data transfer.
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Device Addressing: Each I/O device must have a unique address to enable recognition by the CPU.
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Command Structure: Commands determine how data is read from or written to I/O devices.
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Memory-Mapped vs Isolated I/O: Understanding these two concepts is crucial for memory management in systems.
Examples & Applications
When the CPU wants to print a document, it sends a print command to the printer through programmed I/O, checking if the printer is ready.
On a system with memory-mapped I/O, writing data to the address allocated for a printer is equivalent to executing a memory write operation.
Memory Aids
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Rhymes
In programmed I/O, we check and flow, CPU waits for device status to glow.
Stories
Imagine the CPU as a waiter, constantly checking if the kitchen (I/O device) is ready with your dish before serving it.
Memory Tools
CUDS - Control commands, Unique addresses, Data transfer, Status checks.
Acronyms
DARE - Device Addressing, Active Polling, Read/Write commands, Efficient routines.
Flash Cards
Glossary
- Programmed I/O
A method where the CPU actively checks the status of I/O devices and manages communication through a series of commands.
- Device Service Routine
A program that facilitates communication between the CPU and I/O devices, managing status checks and data transfers.
- Addressing Scheme
The method used to assign unique identifiers to I/O devices, allowing the CPU to communicate effectively.
- MemoryMapped I/O
A technique where I/O devices share the same address space as the main memory.
- Isolated I/O
A method where I/O devices have a separate address space distinct from that of the main memory.
- Control Commands
Instructions given to I/O devices to manage their operations, such as initiating or halting processes.
- Polling
The process by which the CPU periodically checks the status of an I/O device.
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