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This article will explain in detail about the implementation process of an instruction in CPU. The content of the article is of high quality, so the editor will share it with you for reference. I hope you will have a certain understanding of the relevant knowledge after reading this article.

The execution of an instruction in CPU:

The CPU of almost all Feng Bai Neumann computers can be divided into five stages of du: fetching zhi commands, instruction decoding, dao execution instructions, access access numbers, and result write-back.

1. Fetch instruction phase

The Instruction Fetch,IF phase is the process of fetching an instruction from the main memory to the instruction register.

A value in the program counter PC that indicates the location of the current instruction in main memory. When an instruction is fetched, the value in PC is automatically incremented according to the length of the instruction word: (PC) + 1 à PC; if it is a single-word long instruction, (PC) + 2 à PC, and so on.

2. Instruction decoding phase

After fetching the instruction, the computer immediately enters the instruction decoding (Instruction Decode,ID) phase.

In the instruction decoding stage, the instruction decoder splits and interprets the retrieved instructions according to the predetermined instruction format, and identifies different instruction categories and various methods to obtain operands.

In a computer controlled by combinational logic, the instruction decoder produces different control potentials for different instruction opcodes to form different micromanipulation sequences; in the microprogram controlled computer, the instruction decoder uses the instruction opcode to find the entrance of the microprogram that executes the instruction, and executes from this entrance.

3. Instruction execution phase

After the instruction fetch and instruction decoding phase, the execution instruction (Execute,EX) phase is followed.

The task of this stage is to complete the various operations specified in the instruction and specifically realize the function of the instruction. To do this, different parts of the CPU are connected to perform the desired operation.

4. Access several stages

According to the instruction, it is possible to access the main memory and read the operands, thus entering the access number (Memory,MEM) phase.

The task of this stage is to get the address of the Operand in the main memory according to the instruction address code, and read the Operand from the main memory for operation.

5. Result write-back phase

As the last stage, the result Write Back,WB phase "writes back" the run result data of the instruction execution phase to some storage form:

The resulting data is often written to the internal register of CPU so that it can be quickly accessed by subsequent instructions

In some cases, the resulting data can also be written to relatively slow, but cheap, and large-capacity main memory. Many instructions also change the state of the flag bits in the program status word register. these flag bits identify different operation results and can be used to influence the action of the program.

After the instruction is executed and the result data is written back, if there is no unexpected event (such as result overflow, etc.), the computer then obtains the address of the next instruction from the program counter PC, starts a new cycle, and the next instruction cycle will sequentially fetch the next instruction.

On the implementation of an instruction in CPU is shared here, I hope that the above content can be of some help to you, can learn more knowledge. If you think the article is good, you can share it for more people to see.

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