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Today, we're going to discuss programmed I/O. Can anyone tell me what programmed I/O means?
Is it when the CPU directly controls the I/O operations?
Exactly! In programmed I/O, the CPU actively checks the status of an I/O device by polling it. This means the CPU waits for the device to be ready before performing data transfer, which can waste valuable CPU time.
What happens while the CPU is waiting?
Great question! While it's polling, the CPU is unable to perform other tasks, which means efficiency can be reduced.
So, how does the CPU know when the device is ready?
The CPU checks a status bit. If it's set to 1, the device is ready for data transfer.
Can you give us a simple example of this?
Sure! Think of it like waiting for a bus. You keep checking the bus schedule—if it says 'Bus is here,' you get on. Polling is like checking that schedule repeatedly until the bus arrives.
So to summarize, programmed I/O involves the CPU polling for device readiness, which can waste time if not managed correctly.
Now, let’s delve into how we address I/O devices. Can someone tell me why we need to address them?
So we can identify which device we're working with?
Exactly! Just like each house has a unique address, each device requires a unique identifier. This lets the CPU communicate effectively with multiple devices.
What are the main schemes for addressing, then?
There are two primary schemes: memory-mapped I/O and isolated I/O. Memory-mapped I/O uses the same address space for both memory and I/O, whereas isolated I/O has separate spaces.
What’s the advantage of each?
In memory-mapped I/O, you can use the same assembly instructions for both memory and I/O, making it simpler. Isolated I/O, however, allows for many more devices without address conflicts.
So more devices can be connected with isolated I/O?
Yes, that’s right! For example, isolated I/O could support 64k devices when using a 16-bit address bus, whereas memory-mapped might reserve only a few addresses for I/O.
To recap, addressing schemes like memory-mapped and isolated I/O are crucial for managing device communication. They determine how efficiently we can connect multiple devices.
Next, let's talk about the control commands we need for I/O operations. Why do we need to issue commands?
To control what the I/O device does?
Correct! Commands like read, write, and status check help manage I/O devices effectively. Can anyone give me an example of a control command?
How about the command to read data from a device?
Exactly! The 'read' command allows us to retrieve data from an input device, while 'write' sends data to an output device.
What happens if we don't check the status of a device before commands?
Excellent question! If we attempt to use a device that's not ready, we might get incorrect data or encounter errors. That's why status checks are essential.
Are there different categories of control commands?
Yes! We have controlling commands, test commands, and read/write commands. Each serves a specific purpose in device management.
To summarize, control commands are critical for ensuring devices are managed correctly, involving reading, writing, and checking status.
A method where the CPU polls for device readiness before transferring data.
I/O devices share the same address space as memory, allowing for simplified operations.
Uses a distinct address space for I/O devices, enabling greater device connections without conflict.
Commands issued by the CPU to interact with I/O devices, such as read and write.
Polling for data can be a chore, waiting for devices to be ready, is what we often abhor!
Imagine a mailman checking every house on a block (polling) until someone waves from the porch, saying they have mail ready.
PC: Polling Continuously for device readiness!
ISO for Isolated I/O: 'Separate Operations.'
Term
What is programmed I/O?
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Term
Difference between memory-mapped and isolated I/O?
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A method where the CPU actively waits for an I/O device to be ready by polling its status.
A scheme where I/O devices share the same address space with memory, allowing similar operations on both.
A scheme where I/O devices have a separate address space distinct from memory.
Instructions involved in initiating, controlling, and fetching data from I/O devices.
A hardware component that manages communication between the CPU and peripherals.
This section discusses the mapping of I/O devices to a CPU, including programmed I/O and the differences between memory-mapped and isolated I/O.
The section details how I/O devices communicate with a CPU using programmed I/O techniques, emphasizing the inefficiencies of polling. It contrasts memory-mapped I/O, which shares address space with memory, and isolated I/O, which has separate address spaces for memory and I/O devices.
This section elucidates the process of mapping I/O devices to the CPU, showcasing how data transfer can occur efficiently. The key concept here is programmed I/O, where the CPU actively waits and checks (polls) the status of I/O devices, leading to potential wastage of CPU resources. The steps involved in programmed I/O include the CPU initiating an I/O operation and monitoring the status of devices via a status bit.
The section also addresses the addressing schemes necessary for identifying I/O devices. Two primary methods for mapping I/O devices are presented: Memory-mapped I/O and Isolated I/O. In memory-mapped I/O, both memory and I/O devices share the same address space, allowing I/O operations to be treated similarly to memory operations. Conversely, isolated I/O uses distinct address spaces for memory and I/O devices, requiring additional control signals to differentiate between them. This fundamental understanding of I/O mapping aids in grasping how CPUs manage communication with peripherals.