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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 programmed I/O and the importance of device service routines. Can anyone tell me what programmed I/O is?
It's when the CPU is responsible for managing communication with I/O devices, right?
Exactly! Now, why do you think it's important for the CPU to interact with I/O devices using these routines?
So that it can control data transfers effectively?
Yes, but there's also the issue of polling. Can anyone explain what polling means in this context?
Polling is when the CPU continuously checks if a device is ready to send or receive data.
Great explanation! Just remember that while polling allows the CPU to check device status, it can waste CPU time. This is where device service routines become essential.
To sum up, programmed I/O involves the CPU checking a device's status and initiating data transfers through a service routine. Keep these points in mind.
Now that we understand the basics, let’s dive into addressing I/O devices. Why is addressing important?
So we can uniquely identify each device connected to the CPU?
That's correct! Each device requires a unique address. Can anyone mention the two types of addressing schemes for I/O devices?
Memory-mapped and isolated I/O!
Right! In memory-mapped I/O, both memory and I/O devices share the same address space. This makes programming easier since we can use the same commands. However, what might be a drawback?
It limits the number of devices that can be connected, right?
Exactly! And in isolated I/O, we have separate spaces for memory and I/O. This requires special control signals to identify the kind of operation being performed. What is one such control signal?
The I/O/M control signal!
Good job! These methods of addressing are fundamental to how the CPU communicates with various devices. Let's recap: we have memory-mapped I/O and isolated I/O, each with its advantages and disadvantages.
To manage data transfers effectively, we need specific commands. Can anyone name the types of commands involved in I/O operations?
Control, test, read, and write commands!
Great! Let's discuss each one. What do control commands do?
They initiate operations, like moving the printer head or starting a disk drive.
Exactly! And what about test commands?
They check if the device is ready or has power.
Yes! Finally, what do read and write commands accomplish?
Reading takes data from an input device, and writing sends data to an output device.
Perfect! So we need these commands to perform our I/O operations efficiently. Always remember these four command types!
Now, let’s talk in detail about the device service routine. Who can explain what it is?
It's a program that manages the interaction between the CPU and I/O devices during data transfer.
Excellent! Why do we need a routine to manage these transfers?
To ensure that the CPU can carry out other tasks while waiting for the I/O operation to complete.
Exactly! Device service routines allow the CPU to operate more efficiently. Can someone summarize the steps involved in this routine?
The CPU requests the I/O operation, the I/O module processes it, and then the CPU checks the status repeatedly until it's ready for the data transfer.
Great summary! In essence, the device service routine automates monitoring device status to facilitate smoother data transfer. Remember this process as it’s fundamental.
Polling is a CPU's way, checking I/O all day!
Imagine a student waiting at a bus stop (the CPU), checking for the bus (I/O device) to come. They keep looking until the bus arrives, which represents polling status before getting on.
Remember P-C-R for I/O operations: Polling, Commands, Routine.
PC-FOR: Polling, Control commands, Functionality, Operations, Read and write commands.
Term
Programmed I/O
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Term
Device Service Routine
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A method of I/O operation where the CPU directly controls data transfer and polling operations.
The continuous checking by the CPU to determine if an I/O device is ready for data transfer.
A program that runs to manage data transfers between the CPU and I/O devices.
An addressing scheme where I/O devices share the same address space as memory.
An addressing scheme where I/O devices have dedicated address space, separate from memory.
Commands that initiate and control operations of the I/O devices.
Commands used to check the status of I/O devices.
Commands that facilitate data transfer from and to I/O devices.
This section provides an overview of programmed input/output operations and how CPUs interact with I/O devices through service routines.
The section discusses the programmed I/O process, emphasizing the role of the CPU in polling devices for status and the necessity of I/O commands and addressing schemes. It introduces the concept of device service routines, which manage data transfers between the CPU and I/O devices.
In this section, we explore the concept of device service routines within programmed I/O operations. A device service routine is a program executed by the CPU to manage input/output operations between the CPU and I/O devices. The CPU interacts with I/O devices through polling, where it continuously checks the status of the devices to determine if they are ready for data transfer. This process can lead to inefficient CPU usage due to waiting times.
To successfully transfer data, the CPU needs to identify I/O devices through unique addresses. This section also outlines the addressing schemes utilized in I/O, namely:
Three primary commands govern I/O operations:
By understanding how these components work together within programmed I/O, we gain insight into the design requirements for effectively managing data transfers with I/O operations.