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A short class with Sarah and her students. The other ways are under More.
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Today, we are going to discuss the basics of programmed I/O and its steps. Can anyone tell me what programmed I/O is?
Isn't programmed I/O where the CPU communicates with I/O devices through commands?
Exactly! In programmed I/O, the CPU issues commands to the I/O module. Let's break that down. What do you think happens after that command is issued?
The I/O module needs to check if the device is ready?
That's correct! It checks the device status, sets status bits, and the CPU then polls those bits. Why is polling a problem?
It wastes CPU time because it can't do other tasks while waiting?
Right! This waiting can lead to inefficiencies in CPU use. Now, can anyone suggest what the next step after checking the device status might be?
The CPU waits until the device is ready to perform the data transfer?
Exactly! Great job. This process continues until the data transfer is complete.
Now let's talk about how I/O devices are addressed. Who can explain why addressing is important in I/O operations?
It's important because the CPU needs to know what device it is communicating with?
Exactly! Each device must have a unique address, similar to memory addresses. Can anyone think of how these addresses are represented?
They're represented in binary, just like memory addresses?
That's right! Addresses are typically a stream of 0s and 1s. Now, can someone tell me about the difference between memory-mapped I/O and isolated I/O?
Memory-mapped I/O shares the same address space as memory, while isolated I/O has a separate space?
Perfect! In memory-mapped I/O, we can use normal memory instructions, but isolated I/O requires special instructions. Any questions on that?
Let's delve into the commands necessary for the I/O devices. There are three main categories of commands. Who can name them?
Control commands, status commands, and read/write commands?
Great memory! Can someone explain what each type of command does?
Control commands initiate actions on the device, status commands check if the device is ready, and read/write commands transfer data?
Exactly! Why do you think it's essential to have this classification of commands?
It helps organize how we interact with different devices, ensuring we send the right commands?
Spot on! Keeping commands organized helps avoid confusion during data transfer. Let's summarize what we've learned about commands.
To wrap up, how does the interaction between the CPU and I/O devices look in programmed I/O?
The CPU initiates communication, the I/O module checks status, and data is transferred when the device is ready?
Exactly! And what are the potential drawbacks of this method?
The CPU can waste a lot of time polling the device, which isn't very efficient.
Correct! It's crucial to be aware of these inefficiencies when designing systems. Remember, effective communication between the CPU and I/O devices is essential. Any last questions?
A method where the CPU explicitly manages data transfers with I/O devices.
A method where the CPU repeatedly checks device status, which can lead to inefficiencies.
Manages communication between the CPU and peripheral devices.
Memory-mapped and isolated I/O define how devices are referenced in the address space.
When the CPU wants to read data from a keyboard, it sends a command to the I/O module. The module checks the keyboard's status and then transfers data once it is ready.
In a memory-mapped I/O system, the command to send data to a printer could use the same assembly instruction as a command to access memory since both share the same address space.
Polling for a device, checking its status with grace, waiting for readiness in our CPU race.
Imagine a busy office where the manager must check if each worker is ready to provide reports, one by one, instead of getting a bell to ring when they are ready. This is how programmed I/O polices its devices.
Remember 'PCR' for programmed I/O: P for Polling, C for Commands, and R for Read/Write operations.
MAPI: Memory-mapped Addressing Protocol for I/O keeps devices and memory in the same map, but isolated I/O has its space apart.
Term
What is Programmed I/O?
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Term
What is Polling?
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What are Control Commands?
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Isolated I/O vs Memory-mapped I/O?
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A method of data exchange between the CPU and I/O devices where the CPU actively manages the communication through polling.
The process where the CPU checks the status of an I/O device regularly to determine its readiness for communication.
A component that interfaces between the CPU and I/O devices, managing requests and communicating with peripheral devices.
A binary flag set by the I/O module to indicate the state of an I/O device, such as ready or busy.
An addressing scheme where I/O devices share the same address space as the main memory.
An addressing scheme where I/O devices have a separate and distinct address space from memory.
Commands used to initiate operations on I/O devices.
Commands that perform data transfers to or from I/O devices.
This section discusses the key steps involved in programmed I/O, highlighting the need for status checking and data transfer, while addressing CPU inefficiencies.
Programmed I/O involves several critical steps: the CPU requests an I/O operation, the I/O module sets status bits, and the CPU polls those bits to determine when data transfer can occur. This process can lead to CPU inefficiencies as it may waste time waiting for the I/O device to be ready.
Programmed I/O is a method by which a CPU interacts with input/output devices through a sequence of specific commands. The process begins with the CPU issuing a request to the I/O module to perform an operation. The I/O module then checks the status of the device and sets the appropriate status bits indicating whether the device is ready for data transfer. Unlike interrupt-driven I/O, where the I/O module informs the CPU directly, in programmed I/O, the CPU must continuously poll the I/O module to check the status. This continuous checking can lead to inefficiencies as the CPU may waste cycles waiting.
The address of the I/O device must also be specified in the I/O command, similar to how memory addresses are provided when reading from or writing to memory. Furthermore, I/O operations can be grouped into three categories: control commands (to initiate device actions), status commands (to check device conditions), and read/write commands (to transfer data).
There are two addressing schemes for I/O devices: memory-mapped I/O, where I/O devices share the same address space as memory, and isolated I/O, which has separate address spaces for I/O and memory. This segmentation allows for a greater number of devices to be addressed. Understanding programmed I/O is crucial for recognizing how data is transferred between the CPU and I/O devices effectively.