Foreword
Input and output control information transmission means transmits information between the host and the I / O device.
Direct program transfer mode
Direct transfer procedure refers to a fully controlled way data transfer between the host and peripheral devices by a program.
1. unconditional transfer mode
by default peripherals are ready status, do not need to query peripheral idle state.
2. Program Polling Transmission mode
CPU constantly read and test status peripherals by executing the program.
Program interrupt transfer mode
In the program directly transfer mode, CPU need to continue to query the status of peripherals. This is clearly a waste, so we put the initiative to request peripherals. Peripheral interrupt service by sending a request to allow the CPU to execute the interrupt service routine after the response, to be finished, return to the original main CPU to continue their work.
Direct memory access (DMA) mode
The above interrupt transfer mode is also inadequate, for example, the interrupt service routine preparation and debugging complex, and execute the interrupt this process down, take some time.
At this time the introduction of the DMA controller, to the control and operation of the DMA controller, when data to be transmitted, the management of the system bus to the CPU to the DMA controller.
