Suppose you were designing a special?purpose I/O chip to relieve a high?performance workstation of the burden of I/O. What special instructions would you add to the computer’s instruction set? What additional hardware interface would you include – if any?

Question

What will be an ideal response?

Answer 1

A computer does not need special instructions to deal with I/O because peripherals are invariably memorymapped and treated exactly as normal memory locations. Either the processor reads the peripheral or the peripheral generates an interrupt and is then interrogated as part of the interrupt?handling mechanism. You could, for example, create an instruction like TFRin r0,r1,mode that would transfer a block of data from the peripheral to the memory location pointed at by r0. The amount of data is given by the contents of r1 and mode is a constant that defines the operational parameters.

It would make sense to include a DMA capacity in a peripheral so that it can take control of the bus and transfer data autonomously without requiring the processor’s intervention. This requires internal address generators and a bus interface control that can request the bus and generate the necessary signals required to perform the data transfer.