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Goals of the I/O Software
Programmed I/OThis is one of the three fundamentally different ways that I/O can be performed. The programmed I/O was the most simple type of I/O technique for the exchanges of data or any types of communication between the processor and the external devices. With programmed I/O, data are exchanged between the processor and the I/O module. The processor executes a program that gives it direct control of the I/O operation, including sensing device status, sending a read or write command, and transferring the data. When the processor issues a command to the I/O module, it must wait until the I/O operation is complete. If the processor is faster than the I/O module, this is wasteful of processor time. The overall operation of the programmed I/O can be summaries as follow:
Programmed I/O Mode: Input Data Transfer
Programmed I/O Mode: Output Data Transfer
Programmed I/O CommandsTo execute an I/O-related instruction, the processor issues an address, specifying the particular I/O module and external device, and an I/O command. There are four types of I/O commands that an I/O module may receive when it is addressed by a processor:
Advantages of Programmed I/O
Disadvantages of Programmed I/O
Interrupt-Driven I/OInterrupt driven I/O is an alternative scheme dealing with I/O. Interrupt I/O is a way of controlling input/output activity whereby a peripheral or terminal that needs to make or receive a data transfer sends a signal. This will cause a program interrupt to be set. At a time appropriate to the priority level of the I/O interrupt. Relative to the total interrupt system, the processors enter an interrupt service routine. Interrupt I/O InputsFor input, the device interrupts the CPU when new data has arrived and is ready to be retrieved by the system processor. The actual actions to perform depend on whether the device uses I/O ports or memory mapping. Interrupt I/O OutputsFor output, the device delivers an interrupt either when it is ready to accept new data or to acknowledge a successful data transfer. Memory-mapped and DMA-capable devices usually generate interrupts to tell the system they are done with the buffer. Operations in Interrupt I/O
Advantages of Interrupt-Driven I/O
Disadvantages of Interrupt-Driven I/O
I/O Using DMADirect Memory Access is a technique for transferring data within main memory and external device without passing it through the CPU. DMA is a way to improve processor activity and I/O transfer rate by taking-over the job of transferring data from processor, and letting the processor to do other tasks. This technique overcomes the drawbacks of other two I/O techniques which are the time consuming process when issuing a command for data transfer and tie-up the processor in data transfer while the data processing is neglected. It is more efficient to use DMA method when large volume of data has to be transferred. For DMA to be implemented, processor has to share its' system bus with the DMA module. Therefore, the DMA module must use the bus only when the processor does not need it, or it must force the processor to suspend operation temporarily. Operations of Direct Memory Access
Advantages of DMA
1. c; 2. b; 3. d; 4. b; External Links
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When the program has instructions to access the I O device it is called?With programmed I/O, data are exchanged between the processor and the I/O module. The processor executes a program that gives it direct control of the I/O operation, including sensing device status, sending a read or write command, and transferring the data.
In which type of I/O Does the CPU execute special instructions to read and write the I O ports?7.4.2 I/O Mapped Input/Output
I/O-mapped input/output uses special instructions to access I/O ports. Many CPUs do not provide this type of I/O, though the 80x86 does.
What is program controlled I O technique?This I/O technique is the simplest to exchange data between external devices and processors. In this technique, the processor or Central Processing Unit (CPU) runs or executes a program giving direct control of I/O operations.
Is an I/O technique that allows a control unit to directly access main memory?This type of data transfer technique is known as DMA or direct memory access. During DMA the CPU is idle and it has no control over the memory buses. The DMA controller takes over the buses to manage the transfer directly between the I/O devices and the memory unit.
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