25.25.2.4. Categories of I/O Commands

So, basically it is a sensing of status, then using the read write command, then transferring of data; this is the way that we are going to do, but here what is the problem that we have first? CPU needs to wait and poll, it is checking it continuously. So, it cannot do any other work. So, there is a wastage of CPU time.

The section introduces the concept of I/O commands. It outlines the process that occurs during input/output operations, starting with the CPU polling (checking) the status of an I/O device. This means the CPU continuously checks if the device is ready to exchange data. This polling process can waste CPU time, as it cannot perform other operations while waiting.

Imagine you're waiting for a friend to text you back about a movie plan. If you keep checking your phone every second, you're not able to do anything else, such as watching TV or reading a book. This is similar to how the CPU feels while continuously checking the device's status.

So, basically this is now programmed I/O details now you just see these are the simple steps; first one CPU requests to I/O operation that in processor we have shown it, I/O module performs operation, then by looking into the state of the devices I/O module sets the status bit, CPU checks status bits periodically.

This chunk describes the steps in the programmed I/O process. First, the CPU initiates a request for an I/O operation. The I/O module then performs the requested operation and sets a status bit indicating the result of that operation. The CPU periodically checks the status bit to see if the operation is complete. Notably, the I/O module does not directly inform the CPU when the operation is finished, which means the CPU must keep checking.

Think of this like placing an order at a restaurant. You tell the waiter (the I/O module) what you want (the I/O operation), and while your food is being prepared, you keep checking in (polling) to see if it's ready, rather than the waiter coming to tell you when it is.

First of all we have to give the address of the devices from which we are going to take information or to who we are going to give the information. So, this is the addressing scheme, we have to see and will see how we are going to give it then issue some control commands.

This section explains the importance of addressing in I/O commands. Before performing any I/O operation, the system needs to know the specific address of the device it is communicating with. This is known as the addressing scheme, essential for ensuring that data is sent to and received from the correct devices. After determining the address, control commands are issued to initiate processes.

Imagine you’re sending a letter. To ensure it reaches the right person, you must put their address on the envelope. Similarly, in computing, specifying the address of an I/O device is crucial for accurate data transfer.

The command related to control the I/O device can be now look into three different categories. One is your controlling, second one is your test and third one is your read and write.

This section categorizes the types of commands used to control I/O devices into three distinct types: controlling, testing, and read/write commands. Controlling commands initiate actions, testing commands check device status, and read/write commands are used for data transfer.

Think about driving a car: you have control commands like steering to change direction, a speedometer to check your speed (testing), and pushing the accelerator to go faster or the brakes to slow down (read/write commands). Each command serves a unique purpose, just as I/O commands do.

In that particular case we are having two different ways of doing it. One is your memory mapped I/O and second one is your isolated I/O.

This section introduces two methods for mapping I/O devices: memory mapped I/O and isolated I/O. Memory mapped I/O shares the same address space between memory and I/O devices, while isolated I/O has separate address spaces for them. This impacts how data is accessed and processed.

Consider a library: if every book (memory) and magazine (I/O device) are in the same section (memory mapped), it’s convenient but can be crowded. If they’re in separate sections (isolated), it’s easier to find each but requires navigation between spaces.

To identify these things so, we are going to use one more control signal, there will several control signal will come through this particular control bus.

In isolated I/O, a control signal indicates whether the address being sent through the address bus corresponds to a memory location or an I/O device. When this signal is set to 0, it indicates memory; when set to 1, it refers to the I/O device.

Think of a doorbell that distinguishes between visitors (I/O devices) and delivery people (memory). When you press the doorbell, it rings for visitors, but doesn’t ring when the delivery person arrives. This control signal helps the system know whom it is addressing.

Explain how data transfer is performed between CPU and I/O device using programmed I/O techniques.

This chunk summarizes the execution of data transfer using programmed I/O techniques. It describes how a program repeatedly checks the status of an I/O device until it is ready, at which point the program performs the data transfer. This approach ensures efficient communication between the CPU and I/O devices.

This is similar to waiting for a bus. You continually check the time and bus schedule until the bus arrives. Once you see it, you're ready to board (transfer data). The process of waiting and then acting is akin to programmed I/O operations.

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