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Interactive Audio Lesson
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Understanding Programmed I/O
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Welcome class! Today, we’re discussing programmed I/O. Can anyone tell me what that means?
Is it when the CPU directly interacts with I/O devices?
Close! Programmed I/O involves the CPU polling I/O devices to check their status. This means the CPU waits for the device to indicate it's ready for data transfer.
So, how is it different from other methods?
Good question! Unlike interrupt-driven I/O, where devices signal the CPU, programmed I/O requires the CPU to continuously poll the device status, which can waste processing time. Remember: Polling equals waiting.
What happens when the device is ready?
Once ready, the CPU performs the data transfer. Understanding programmed I/O is crucial because it sets the foundation for how we interact with hardware.
Let's summarize: Programmed I/O involves the CPU actively polling I/O devices for readiness to transfer data, which can lead to inefficient CPU time usage.
Addressing I/O Devices
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Now, let’s address how we locate I/O devices. Why do you think a unique address is essential?
So that the CPU knows where to send data?
Exactly! Each I/O device must have a unique address, just like memory addresses, to avoid conflicts. This is called the addressing scheme.
Are there different ways to address devices?
Yes! We have two primary types: Memory-Mapped I/O and Isolated I/O. In memory-mapped I/O, I/O devices share the same address space as memory.
Then what’s isolated I/O?
In isolated I/O, the I/O devices have separate address spaces, allowing for more devices to be managed effectively. Think of it as two roads for data traffic.
To summarize, we need a unique addressing scheme for proper communication with I/O devices, which can either share the address space with memory or have isolated addresses.
Control Signals and Commands
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We’ve discussed addresses, but what commands do we need for I/O operations?
Do we need commands to start the operation?
Correct! Control commands initiate processes. We use commands to read and write data, check status, and send control signals to devices.
How do these commands interact with the CPU?
Excellent! The CPU sends specific commands to the I/O module, like 'read' and 'write', to perform the desired operations. These commands are critical in managing data effectively.
In summary, control commands and signals are essential for regulating I/O operations, enabling data transfer and device communication.
Differences Between I/O Mapping Styles
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Let’s wrap up by comparing memory-mapped I/O with isolated I/O. How would you explain the differences?
Memory-mapped I/O uses the same address space for memory and devices, right?
Correct! That means it’s limited by available memory addresses. In contrast, isolated I/O provides separate spaces for devices.
What’s a benefit of isolated I/O?
Isolated I/O can connect many more devices, making it scalable. However, it requires some additional control signals to differentiate between memory and I/O operations.
To summarize, memory-mapped I/O shares addresses, while isolated I/O maintains distinct spaces, impacting I/O operation complexity and device limits.
Introduction & Overview
Read a summary of the section's main ideas. Choose from Basic, Medium, or Detailed.
Quick Overview
Standard
In this section, the focus is on the methods of data transfer between the CPU and I/O devices. It explains programmed I/O, where the CPU polls the I/O status, the addressing schemes for devices, and the mechanisms of memory-mapped and isolated I/O, along with the necessary I/O commands required for effective operation.
Detailed
Mode of Transfer
In this section, we explore the various modes of data transfer between the CPU and input/output (I/O) devices, specifically focusing on programmed I/O. The CPU often needs to monitor the status of I/O devices continuously, resulting in polling that can waste CPU time. Thus, programmed I/O allows the CPU to request operations wherein the I/O module performs actions based on device status. Notably, the CPU checks the status bit to ensure that the device is ready before data transfer.
Key requirements for utilizing I/O devices include addressing schemes and control commands. Addressing schemes uniquely identify each device while facilitating proper communication. Control commands are structured to manage device operations effectively, including reading from and writing to different hardware components.
Options for I/O address mapping include 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 to the residual addresses left after allocating memory. In contrast, isolated I/O provides separate address spaces for memory and I/O operations, allowing for a greater number of connected devices. Control signals, particularly the IO/M bar signal, distinguish between memory operations and I/O commands, determining where data should be directed.
An understanding of programmed I/O allows us to recognize how data is managed within computing systems, improving efficiency and effectiveness in CPU-I/O communication.
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Programmed I/O Overview
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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.
So, basically you just see that if we are going to connect something like that this processor is going to, maybe 1 bit of the status register is going to continuously monitor and if it is set to 1; that means, device is ready, then it is going to perform the transfer operation. So, this is our programmed I/O.
Detailed Explanation
Programmed I/O is a method where the CPU directly controls I/O operations by checking the status of the device. This involves repeatedly querying a status register to see if the device is ready to send or receive data. However, this method has a significant downside: while the CPU is waiting (or polling) for the device to be ready, it cannot perform other tasks, leading to inefficient use of CPU resources. Essentially, the CPU spends time doing nothing productive, simply waiting.
Examples & Analogies
You can think of programmed I/O like waiting in line at a coffee shop. If you stand there waiting, you can’t do anything else—like checking your phone or sending an email—until it's your turn to place an order. Similarly, the CPU is 'standing in line' waiting for the device to be ready, which wastes time.
Steps of 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.
Detailed Explanation
The process of programmed I/O involves several key steps: First, the CPU sends a request for an I/O operation to the I/O module. Once the I/O module receives this request, it performs the required operation, such as reading data from an input device or writing data to an output device. During this time, the I/O module constantly checks the state of the device and updates a status bit to indicate whether the device is ready for the next operation. Meanwhile, the CPU periodically checks this status bit to determine if it can proceed with the data transfer.
Examples & Analogies
Imagine asking a friend to get a book from a shelf. You wait for your friend to tell you when the book is ready. While your friend is fetching it, you keep checking in to see if they are done yet. This waiting and checking represents the CPU sending requests and polling the I/O module for status updates.
I/O Commands and 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
In order to interact with I/O devices, specific I/O commands must be sent from the CPU. One critical aspect of these commands is addressing: each I/O device needs a unique identifier (or address) so that the CPU can communicate accurately. Just like houses have addresses for delivery services, I/O devices also need addresses to ensure that the commands are sent to the right location.
Examples & Analogies
Consider sending a letter in the mail. You need to put the correct address on the envelope so the postal service can deliver it to the right person. Similarly, the CPU identifies each I/O device with a unique address to send commands to the appropriate hardware.
Modes of I/O Mapping
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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
When addressing I/O devices, there are two primary methods: Memory-Mapped I/O and Isolated I/O. In Memory-Mapped I/O, I/O devices share the same address space as the memory, allowing the same instructions used for memory operations to also access I/O devices. In contrast, Isolated I/O has separate address spaces for memory and I/O devices, requiring different instructions to control I/O devices. This separation allows for a greater number of devices, but also necessitates additional logic to distinguish between memory and I/O addresses.
Examples & Analogies
Think of Memory-Mapped I/O like living in a community where every house and business uses the same street address system. You can easily send guests to either a home or a business without confusion. Conversely, Isolated I/O is like having two different neighborhoods: one for houses (memory) and another for businesses (I/O devices). You need to know which neighborhood you are in to send guests correctly, as each uses a different addressing system.
I/O Control Signals
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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, we are going to use one more control signal.
Detailed Explanation
To manage the differences between memory and I/O addressing, a control signal is utilized. This signal helps the CPU determine whether an address on the bus corresponds to a memory location or an I/O device. For example, control signals can indicate whether to read data from memory or an I/O device, allowing the CPU to execute the appropriate operations depending on the address type.
Examples & Analogies
Imagine a traffic light at an intersection. It directs cars whether to stop or go, helping drivers know when it's safe to proceed. Similarly, control signals direct the CPU by indicating whether it should perform a memory operation or an I/O operation based on the address received.
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 transfer method where CPU polls devices for readiness before executing data transfer.
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Polling: Continuous status checking of I/O devices by the CPU.
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Addressing Schemes: Systems to assign unique addresses to devices for identification.
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Memory-Mapped I/O: Sharing the address space between memory and I/O devices.
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Isolated I/O: Separate address spaces for memory and I/O devices to allow more connections.
Examples & Real-Life Applications
See how the concepts apply in real-world scenarios to understand their practical implications.
Examples
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An example of programmed I/O would be a CPU that continuously checks a printer's status to see when it is ready to print.
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Using memory-mapped I/O, a CPU reads from an address that corresponds to an I/O device using the same instruction set as it would for memory reads.
Memory Aids
Use mnemonics, acronyms, or visual cues to help remember key information more easily.
🎵 Rhymes Time
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Polling is like calling, asking 'Are you ready?' before data we are letting.
📖 Fascinating Stories
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Imagine a teacher checking if students are ready to present before starting the presentation—this reflects programmed I/O where readiness must be verified.
🧠 Other Memory Gems
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For I/O, remember 'Read, Write, Check' to recall the command sequence.
🎯 Super Acronyms
I/O can be remembered as 'Input/Output is Orderly' to emphasize orderly operations in data transfer.
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 transfer where the CPU actively polls the I/O device for readiness before performing data transfer.
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Term: Polling
Definition:
The process by which the CPU regularly checks the status of an I/O device.
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Term: MemoryMapped I/O
Definition:
An I/O scheme where I/O devices share the same address space as memory.
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Term: Isolated I/O
Definition:
An I/O mapping method that uses separate address spaces for I/O devices and memory.
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Term: Control Commands
Definition:
Instructions sent by the CPU to an I/O device to manage operations such as reading, writing, or controlling the device.