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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 discuss polling and how it affects the CPU's efficiency. Can anyone tell me what polling is?
Isn't it when the CPU checks if a device is ready repeatedly?
Exactly! Polling is where the CPU continuously checks the status of an I/O device. This can lead to CPU time being wasted. Why do you think that is?
Because while it's checking, it can't do anything else?
Exactly! So, polling can lead to inefficiencies. Hence, CPUs require a better way to manage I/O devices. Let's remember: 'Poll to know, but don’t commit to slow!' That's our first memory aid today.
Now that we understand polling, let’s talk about programmed I/O. What are the steps involved in conducting programmed I/O?
First, the CPU requests an I/O operation.
That's right! Then what happens after that request?
The I/O module performs the operation and sets the status bit accordingly.
Excellent! The CPU will then check this status bit until it is ready. Let's remember the step sequence: Request - Perform - Check.
Next, we need to identify how I/O devices are addressed. What is important here?
Each device must have a unique address!
Right! Each I/O device must have a unique address, similar to memory addressing. Can anyone name the two main addressing schemes?
Memory-mapped I/O and isolated I/O!
Good! Memory-mapped I/O shares address space with general memory while isolated I/O keeps them separate. Now, which one allows for more devices to be connected?
Isolated I/O would allow more devices since it has separate address space.
Correct! Just remember: 'Isolated is spacious, while mappers are closer!' That's our next memory aid.
The process by which a CPU maintains checks on I/O device status.
The unique identifiers assigned to I/O devices for operational reference.
An I/O addressing scheme using shared memory addresses.
An I/O addressing method with distinct address spaces for devices and memory.
When polling starts to loom, CPU's in a waiting room.
Imagine a teacher waiting by the door to check if students are ready instead of teaching the rest of the class. That's similar to how polling works.
P.A.S. - Polling, Addressing, Scheme. Remember the sequence of key concepts.
P.I.O. - Polling Is Overhead. To remember that polling has drawbacks.
Term
What is Polling?
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Term
Define Programmed I/O.
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Term
What are the two addressing schemes for I/O devices?
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A method where the CPU repeatedly checks the status of an I/O device to determine readiness for data transfer.
A technique where the CPU directly controls I/O operations through a program, checking for the status of devices.
The method used for assigning unique identifiers (addresses) to I/O devices.
An addressing scheme where I/O device addresses overlap with memory addresses.
An addressing scheme where I/O devices have separate address spaces from memory.
The section discusses the inefficiencies of polling in CPU operations, particularly in the context of I/O operations.
In this section, we explore the concept of polling, where the CPU continuously checks the status of an I/O device, leading to wasted CPU time and inefficient processing. The section also covers programmed I/O and the addressing schemes necessary for I/O operations, including memory-mapped and isolated I/O.
Polling is a method where the CPU repeatedly checks the status of an I/O device to determine if it is ready for data transfer. This leads to significant CPU time wastage as the processor cannot conduct other tasks while waiting. In programmed I/O, the CPU initiates an I/O operation and then continuously polls a status bit to see if the device is ready. This method does not allow the CPU to perform any other operations during polling, hence it is a less efficient use of resources.
Key concepts also include the need for addressing within I/O operations. Each I/O device must have a unique address for identification, and the I/O module must issue control commands to manage these operations effectively. The two main addressing schemes discussed are: 1) Memory-Mapped I/O, where the I/O devices share the same addressing space with memory, and 2) Isolated I/O, in which separate address spaces for memory and I/O devices are used, significantly increasing potential device connections. Both methods have their applications and situations where they are more advantageous than the other. Ultimately, programmed I/O requires effective communication between CPU and I/O devices through these established commands and addressing schemes.