Computer system knowledge--input and output technology

First, understand that a concept of input-output technology is the processing of data between memory and peripheral devices, and the interaction process is controlled by the CPU.

program control input and output

The main input and output methods of the program are four kinds:

Unconditional Delivery

Computer systems have some simple external devices that, when they start working, are ready to receive data from the CPU or ready to be called by the CPU at all times. This is an unconditional transmission.

Query Method

Unconditional delivery is also conditional on the fact that peripherals are always ready for data, or are running slow peripherals. For peripherals that are not always ready, it is the way that a slow or medium-speed device uses the query, which requires peripherals to provide device status.

The input and output can be achieved by asking for the status of the peripheral.

There are multiple peripherals in the query mode, it is necessary to query all the peripherals first, if there are resources to directly use, and then query the back.

Interrupt Mode

CPU in the process of executing a program, the other events occurred, the CPU to deal with the event (interrupt recognition), the processing of the event is to stop (interrupt request) and save the "event scene" (Breakpoint protection), when the unexpected event, and then back to the original termination of the event processing (interrupt source recognition) , this process is the interrupt process.

The figures in turn represent the order of execution, and the illustration represents only the main steps

The interrupt mode can improve the efficiency of the CPU, because the CPU can respond to the peripheral in real time without waiting for all CPU events to be processed.

Direct Memory (DMA) modeDMA (Direct Memory Access), the use of large integrated circuit chip DMAC is necessary to achieve DMA mode.
1, the peripheral to the DMAC issued a DMA request; 2, then dmac to the CPU according to the hold signal to submit the DMA request; 3, the CPU completes the current bus cycle, immediately to the DMA request to make corresponding; 4, waiting for the CPU to execute, DMAC start to the bus real-time control and send DMA corresponding signal to the peripheral; 5. After the DMA sends out the signal, it realizes the data exchange between memory and peripheral, or memory and memory.
6, Dmac after the execution of external tasks, through the CPU to send hold signal, REVOKE the DMA request.
the above is a full DMA mode of data exchange.
input and output technology can be said to realize the important channel of human-computer interaction, people and computers for dialogue and exchange, it is necessary through this technology to communicate our ideas to the computer, and then the computer will be the results of the show to us.
next look at the bus that plays an important role in the computer system, confined to space, see the next blog post.


"Computer system knowledge--CPU"
"Computer system knowledge-memory"
"Computer system knowledge-input and output technology"

Computer system knowledge--input and output technology