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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 dive into the world of I/O Command Execution, specifically focusing on programmed I/O. Can anyone tell me what programmed I/O means?
I think it means that the CPU directly controls the I/O operations, and it has to check when the device is ready.
Exactly! That's a great start. In programmed I/O, the CPU must periodically check the status of I/O devices to see if they're ready. This process can lead to wasted CPU time, as the CPU can't perform other tasks while waiting. This is called polling.
So, what’s the first thing the CPU does when it wants to perform I/O?
The CPU first requests the I/O operation from the I/O module. After that, it checks the status to see if the operation can be executed.
How does the CPU know when the device is ready?
Good question! The I/O module sets a status bit that the CPU checks periodically. If the bit indicates that the device is ready, then the data transfer can occur.
To sum up, programmed I/O involves a series of steps starting from CPU requesting an I/O operation to checking the status bit until it can perform the operation.
Addressing in I/O Operations
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Let's shift our focus to the addressing scheme used in I/O devices. Why do you think it’s important to uniquely identify each I/O device?
So that the CPU knows which device to communicate with, right?
Correct! Addressing is crucial. Each I/O device must have a unique address, just like memory locations, to ensure proper communication. There are two methods: memory-mapped I/O and isolated I/O. Can anyone differentiate between the two?
In memory-mapped I/O, I/O devices share the address space with memory, right?
Yes! And how about isolated I/O?
Isolated I/O keeps separate address spaces for I/O and memory devices.
Exactly! This method allows a larger number of devices since both memory and I/O can have their own address space. Now, remember the control signal `I/O/M`. It tells the system whether the address is for memory or an I/O device.
To wrap up, addressing for I/O operations is vital, and understanding the difference between memory-mapped and isolated I/O can help us optimize our systems.
Commands for I/O Devices
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Now that we understand how I/O devices are addressed, let's talk about the commands that we need to perform I/O operations. What types of commands do you think are necessary?
I assume there are commands for reading and writing data!
Absolutely! There are three main categories of commands: control commands, test commands, and read/write commands. Can someone give an example of a control command?
A command to initiate a printer, like setting the print head position, would be a control command.
Exactly! The control commands are crucial as they ensure devices are set up correctly before data transfer. What about test commands?
Those could be commands that check if a device is powered on or ready to operate.
Right! And finally, we have the read and write commands that actually transfer data between the CPU and I/O devices. For instance, the `IN` command fetches data from a device, and the `OUT` command sends data to a device.
In summary, effective I/O operation relies on using the appropriate commands for control, testing, and data transfer.
Data Transfer through Programmed I/O
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We've covered commands and addressing, but how does actual data transfer happen between a CPU and an I/O device using programmed I/O?
Is it like running a program that keeps checking if the device is ready?
Exactly! We write a device service routine, which involves a loop that checks the status bit. Once the device is ready, the routine executes the remaining logic to transfer data.
So, the program controls both the check for readiness and the actual data transfer?
Yes! That’s how programmed I/O works. It's significant because it allows us to automate the process while continuously monitoring the I/O status.
Are there any drawbacks to this method?
Yes, the main drawback is inefficiency due to CPU polling. The CPU is either waiting for the device or performing the operations sequentially, which can lead to delays.
To summarize, programmed I/O enables data transfer through iterative checking, but it can lead to CPU inefficiencies.
Introduction & Overview
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Quick Overview
Standard
In this section, the I/O command execution process is outlined, detailing the interactions between the CPU and I/O devices via programmed I/O. The significance of unique addressing for each I/O device is emphasized, alongside the distinctions between memory-mapped I/O and isolated I/O systems.
Detailed
Detailed Summary of I/O Command Execution
This section delves into the processes involved in I/O command execution, primarily focusing on programmed I/O methodology. When the CPU initiates an I/O operation, it must first request this operation and then monitor the associated status register to determine whether the device is ready for data transfer. This constant polling can lead to CPU time wastage, as the CPU cannot perform other tasks during this wait.
Programmed I/O Steps: The steps involved in programmed I/O include:
1. CPU requests an I/O operation.
2. The I/O module performs the necessary operation.
3. The I/O module sets a status bit to indicate device readiness, and the CPU has to check this bit periodically.
Although programmed I/O allows simple device communication, it has limitations such as requiring manual polling and delaying CPU tasks.
I/O Addressing Schemes: Additionally, for successful data transmission, each I/O device must be uniquely identified via an addressing scheme. There are two main types of addressing: memory-mapped and isolated I/O. In memory-mapped I/O, both memory and I/O devices share the same address space, whereas in isolated I/O, dedicated separate address spaces are utilized for the two categories, enhancing the number of devices that can be connected. The control signal I/O/M distinguishes between memory and I/O addresses.
By placing I/O operations alongside memory operations in the case of memory-mapped I/O, a consistent instruction set can be used; however, isolated I/O requires specific instructions for device operations. This section concludes with an overview of how data transfer occurs using programmed I/O, illustrating its architecture and how addressing is integral to these operations.
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Overview of I/O Command Execution
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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
In I/O command execution, the process starts with the CPU checking the status of an I/O device to see if it is ready for communication. This involves sending a read or write command and transferring data accordingly. However, a significant issue arises because the CPU has to wait for the device to be ready. This waiting involves constantly checking the device status, which means the CPU cannot perform other tasks during this time. This is inefficient because the CPU's time is wasted while it waits.
Examples & Analogies
Think of it like a waiter in a restaurant who keeps checking if a specific meal is ready while ignoring other customers. The waiter spends a lot of time waiting for that one meal to be prepared, instead of serving other guests.
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
Programmed I/O consists of several steps. First, the CPU makes a request for an I/O operation. The I/O module then performs the necessary operation by checking the device's state and setting a status bit. The CPU must check this status bit at intervals (polling) to determine when the device is ready. This process does not involve interrupts, meaning the I/O module does not notify the CPU directly, leading to potential delays in the operation.
Examples & Analogies
Imagine a parent waiting for a child to finish cleaning their room. The parent keeps checking periodically to see if the room is done. The child doesn't inform the parent when the task is completed; instead, the parent has to keep asking. This results in the parent being occupied with waiting instead of doing something else.
I/O Command Requirements
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Now after that to perform work with the I/O module or input output devices what are the basic requirements. Already I have mentioned that we need some commands I/O commands...
Detailed Explanation
To manage I/O operations effectively, certain requirements must be met, primarily involving specific commands. These commands allow the CPU to identify the I/O modules (using device addresses), perform control commands to initiate processes, and handle data transfer between the processor and the devices. Each command serves a distinct function, whether it’s reading, writing, or controlling device state.
Examples & Analogies
Think of sending a letter. The address on the envelope (device address) tells the postal service where to send the letter. Before sending, you write a request (control command) like requesting an urgent delivery. When the letter is sent, this function includes the ink (data) that represents what you wish to communicate.
Addressing Scheme
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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...
Detailed Explanation
The I/O addressing scheme is critical for the CPU to communicate with peripheral devices. There are mainly two methods of mapping: memory-mapped I/O, where device addresses fall within the same address space as memory, and isolated I/O, where separate address spaces exist for memory and I/O devices. This means that the same address can represent different things based on the context, helping to simplify communication with devices.
Examples & Analogies
Consider a library where books and magazines are stored separately (isolated I/O), as opposed to a single section where both can be found together (memory-mapped I/O). With the first, you might need different keys for sections, while in the latter, a single key can access everything. Understanding this helps the CPU know how to retrieve or send information to devices effectively.
Memory-Mapped vs. Isolated I/O
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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
In memory-mapped I/O, both memory and I/O devices share the same address space, allowing for a simpler approach where normal memory instructions can be used for device interaction. In contrast, with isolated I/O, there is a distinct address space dedicated solely to I/O devices, allowing for more devices to connect, but requiring different instructions to communicate with them. This distinction can lead to variations in how instructions are executed based on the type of I/O mapping used.
Examples & Analogies
Imagine a car with a combined fuel gauge and speedometer (memory-mapped) versus one with separate dials for each (isolated I/O). In the first, you only need to check one device for both readings, while in the second, you have to check two different units for specific data.
I/O Command Execution Overview
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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...
Detailed Explanation
I/O commands like 'in' and 'out' are crucial for facilitating data transfers between the CPU and I/O devices. The 'in' command retrieves data from an I/O device, while the 'out' command sends data to an I/O device. These commands help streamline interaction with peripherals, allowing for straightforward data handling.
Examples & Analogies
Envision playing music on a speaker. The 'in' command represents pressing the play button to start the sound coming from the device, while the 'out' command is akin to sending a song playlist from your phone to be played. Each command serves a purpose for effective communication with your devices.
Device Service Routine in Programmed I/O
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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...
Detailed Explanation
A device service routine is a program that manages the I/O operation in a loop. This routine continuously checks if the device is ready to perform an operation. Once the device indicates it’s ready, the routine will execute the data transfer. This morning approach ensures systematic handling of the devices without overwhelming the CPU with constant checks.
Examples & Analogies
Think of it like checking your email. You check your inbox at intervals instead of continuously refreshing it. Once you see a new message (the device is ready), you open and read it (performing the I/O operation). This approach makes your work more organized and manageable.
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 technique for executing I/O commands where the CPU is responsible for polling device status.
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Polling: The CPU frequently checks the device status, leading to potential inefficiency.
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Status Bit: A binary flag set by the I/O module to indicate readiness for data transfer.
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Memory-Mapped I/O: A scheme where I/O devices share the same address space as memory.
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Isolated I/O: A method where separate address spaces are dedicated to I/O devices 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 the CPU wants to read data from a keyboard, it continuously checks the status bit to decide when the keyboard is ready to send data.
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In a memory-mapped I/O scheme, the address range 0xFFFF to 0xFFFF could be reserved for devices like printers, allowing load and store operations to treat them as if they were memory addresses.
Memory Aids
Use mnemonics, acronyms, or visual cues to help remember key information more easily.
🎵 Rhymes Time
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In I/O device land, the CPU does stand; polling away, its time slips through sand.
📖 Fascinating Stories
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Imagine a device shop where each device has a special badge. The CPU asks each device if it's ready, checking them one by one, losing time while it waits.
🧠 Other Memory Gems
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To remember the steps in Programmed I/O: R - Request, S - Status check, T - Transfer data.
🎯 Super Acronyms
P.I.O. - Polling I/O Operations
- 'Polling' for readiness
- 'Input/Output' commands processed.
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 where the CPU directly controls I/O devices and checks their status to perform data transfers.
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Term: Polling
Definition:
The continuous checking of the status of an I/O device by the CPU.
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Term: Status Bit
Definition:
A binary indicator set by the I/O module to signal if it is ready for a data transfer.
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Term: MemoryMapped I/O
Definition:
An I/O addressing scheme where I/O devices share the same address space as memory.
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Term: Isolated I/O
Definition:
An I/O addressing scheme where memory and I/O devices have separate address spaces.
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Term: Control Commands
Definition:
Instructions sent to I/O devices to prepare them for data operations.
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Term: Read/Write Commands
Definition:
Commands that facilitate data transfer from and to I/O devices.