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A short class with Sarah and her students. The other ways are under More.
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Today, we're going to learn about programmed I/O, which is a method where the CPU polls devices to check if they're ready for data transfer. Can anyone tell me what they think polling means?
Isn't polling when the CPU keeps checking the device status repeatedly?
Exactly! That's right, Student_1. Polling means the CPU actively checks the status of an I/O device continuously. This can lead to inefficiency because while it's checking, it can't do other work. Do you see how that could waste CPU time?
So, why don't we just have the device tell the CPU when it's ready?
That's a great question, Student_2! It is possible with interrupt-driven I/O, where the device informs the CPU. However, in programmed I/O, the CPU relies on its checks. Let's remember this inefficiency by using the acronym CPU—Constantly Polling Units.
So, what happens if a device isn’t ready?
Good point, Student_3! If a device isn’t ready, the CPU may abandon the operation or wait. We’d have to manage this carefully to avoid wasted resources.
To summarize this session, programmed I/O is a method where the CPU polls devices to check if they are ready for data transfer, which can consume a lot of CPU time.
Now, let’s discuss how we identify and address I/O devices. Student_4, what do you think is essential for addressing these devices?
Maybe unique addresses for each device?
Exactly, Student_4! Each I/O device must have a unique identifier. Addressing I/O devices is similar to how we identify memory addresses. Why do you think it’s important to have unique addresses?
So the CPU knows where to send or receive data?
Correct! Unique addresses ensure that the CPU knows exactly where to read from or write to. Can anyone suggest a way to remember the types of commands we need to use for these operations?
What about CONTROL, STATUS, and DATA for the commands?
Fantastic mnemonic, Student_2! 'CSD' can remind us of Control, Status, and Data commands that we'll be using for managing devices. To recap, addressing allows the CPU to uniquely identify devices, and we use commands categorized as Control, Status, and Data for operations.
Next, we are talking about how I/O devices are mapped to a system’s architecture. Can anyone remember the two types of mapping we discussed?
Isolation I/O and memory-mapped I/O?
Spot on, Student_3! Memory-mapped I/O and isolated I/O! Can someone explain how memory-mapped I/O works?
In memory-mapped I/O, the same address space is shared by memory and I/O devices?
That’s right! This means I/O devices are identified using regular memory commands. What about isolated I/O, Student_4?
In isolated I/O, memory and I/O have separate address spaces.
Excellent! In isolated I/O, we have different address spaces for memory and I/O operations, which can allow more devices to be connected without conflicts. Let's use the acronym 'ISO' to remember isolated I/O. Summarizing today, we learned about two I/O mapping techniques: memory-mapped I/O shares the address space with memory, while isolated I/O has separate spaces.
As we wrap up, let’s summarize the control commands and their significance within our discussions. Student_1, what are the three types of control commands we’ve talked about?
Control, Status, and Data commands!
Great recall! Control commands initiate operations, Status commands check device readiness, and Data commands perform the transfer. Who remembers why we need the unique addressing scheme for I/O devices?
So the CPU can communicate with each device accurately and efficiently.
Exactly! Proper addressing helps in smooth communication. As a final recap today, we learned about programmed I/O and two mapping techniques for I/O devices, along with control commands functionalities and importance.
The method of active CPU polling for I/O device readiness.
Commands used to control I/O operations, including initiating transfers.
The unique identification process for I/O devices necessary for communication.
I/O devices and memory share the same address space allowing unified command usage.
A method where memory and I/O devices have separate address spaces.
An example of programmed I/O is a keyboard where the CPU polls its status to determine if a key has been pressed.
For memory-mapped I/O, a printer and a hard drive can be controlled using memory commands since they share the memory address space.
In isolated I/O, when accessing a scanner, the CPU must access a separate address space specifically designated for I/O communication.
Polling can make CPU drear, waiting for I/O to appear.
Once a CPU traveled a road called Polling Lane, where it continually asked every device, 'Are you ready yet?' Sometimes the devices would respond with a 'yes,' but many times, they wouldn’t. This road was long and tiring, and the CPU couldn't stop for snacks (other tasks).
Remember ISO for Isolated I/O, as it keeps devices in their own unique zones.
CSD for Control, Status, Data when addressing devices, it’s not just a matter of fate!
Term
What is programmed I/O?
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Term
What are the two types of I/O mapping?
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Term
What are control commands?
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A component that manages communication between the CPU and I/O devices.
A technique where the CPU actively polls devices to check their status and readiness for data transfer.
The continuous checking of a device's status by the CPU.
A method of using the same address space for both memory and I/O devices.
A method where memory and I/O devices operate in separate address spaces.
Instructions that manage operations and states of I/O devices.
Commands responsible for the read and write operations between CPU and I/O devices.
This section covers the significance and mechanics of control commands in I/O operations, including programmed I/O and the addressing schemes for devices.
The section explains programmed I/O, highlighting that the CPU must poll devices for readiness, leading to inefficient CPU usage. It delves into I/O command requirements, addressing schemes, and distinct methods for mapping I/O devices, including memory-mapped I/O and isolated I/O.
This section outlines the essential mechanisms and commands utilized in Input/Output (I/O) operations within computer systems. The discussion begins with programmed I/O, where the CPU continuously polls the status of I/O modules to determine if they are ready, leading to a significant waste of CPU time as it cannot perform other tasks simultaneously.
Key Processes in Programmed I/O:
To perform effective I/O operations, a comprehensive set of commands and a precise addressing scheme are necessary. The addressing scheme ensures that every device has a unique identifier, akin to memory locations. Communication with devices involves issuing control commands that fall into three categories:
IN for input and OUT for output).There are two primary methods to map I/O devices to the processor: memory-mapped I/O and isolated I/O.
The significance of these operations and commands lies in their optimization of I/O device management and facilitating efficient CPU performance.