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Direct program control refers to the input of peripheral data / The output process is in CPU Completed under the control of the execution program .
This method is divided into unconditional transmission and long beard query ;

Peripheral data is always ready , It can receive unconditionally at any time CPU Output data sent ;
Can also unconditionally report to CPU Provide data ;

In this way ,CPU Relevant procedures need to be implemented , To see if the data is ready ; So this kind of query efficiency is very low ;
adopt CPU Execute programs to query the status of peripherals , Determine whether the peripheral is ready to receive data or to CPU Input data .
According to the state of the peripheral ,CPU It also provides targeted input and output services for peripherals ;
Usually , There can be many different peripherals in a computer system , If these peripherals work in query mode , be CPU These peripherals should be queried one by one , When you find out which peripheral is ready, you can service that peripheral ;
This way, CPU Regular training is needed I/O The state of the system , To reduce the CPU The efficiency of , And it cannot make real-time response to external emergencies ;

3、 ... and 、 Interrupt mode

Return some interrupted signals to CPU,CPU Temporarily suspend the implementation of the current procedure , Turn to the interrupt handler that serves a random situation ;
Automatically resume the execution of the original program after processing ;

In order to reduce the number of programs in direct control mode CPU Wait time and improve the degree of parallel work of the system ;
Used to control peripheral devices and memory and CPU The data transmission between is called interrupt mode ;

Wake up the blocked driver ;
Protect the interrupted process CPU Environmental Science ;
Analyze the cause of the interruption , Transfer to the corresponding device interrupt handler ;
Interrupt processing ;
Recovery is interrupted i Site of process ;

Direct memory access （DMA） It refers to data in memory and I/O Direct block transfer between devices ;
That is, in memory and I/O The process of transferring a data block between devices , Unwanted CPU Any interference in ;
It only needs CPU Start at the beginning of the process （ That is, send... To the equipment “ Send a piece of data ” The order of ） And the end of the process （CPU Know whether the process is finished and whether the next operation is ready by polling or interrupt ） Time processing , The actual operation is controlled by DMA Hardware direct execution complete ;
CPU Do something else during this transmission ;
DMA To reduce the CPU Yes I/O Control of operation , bring CPU The efficiency of .

Is a processor with special functions , Also known as channel mode ;
It shares CPU Part of the function , It can realize the unified management of peripheral devices , Complete the data transmission between peripheral devices and main memory ;
The channel mode is greatly improved CPU Work efficiency , However, this efficiency improvement is at the cost of adding more hardware ;