Pipelining and Arm processing

PIPELINING

          The Process of fetching the next instruction while the current instruction is being executed is called as “pipelining”. Pipelining is supported by the processor to increase the speed of program execution. Increases throughput. Several operations take place simultaneously, rather than serially in pipelining. The Pipeline has three stages fetch, decode and execute as shown in Fig.

The three stages used in the pipeline are:

(i) Fetch : In this stage the ARM processor fetches the instruction from the memory.

(ii) Decode : In this stage recognizes the instruction that is to be executed.

(iii) Execute 2 In this stage the processor processes the instruction and writes the result back to desired register.

If these three stages of execution are overlapped, we will achieve higher speed of execution. Such pipeline exists in version 7 of ARM processor. Once the pipeline is filled, each instructions require s one cycle to complete execution.

TYPES OF PIPELINE

It is divided into 2 categories:

1. Arithmetic Pipeline
2. Instruction Pipeline

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Arithmetic Pipeline

Arithmetic pipelines are usually found in most of the computers. They are used for floating point operations, multiplication of fixed point numbers etc. For example: The input to the Floating Point Adder pipeline is:

X = A*2^a

Y = B*2^b

Here A and B are mantissas (significant digit of floating point numbers), while a and b are exponents.

The floating point addition and subtraction is done in 4 parts:

1. Compare the exponents.
2. Align the mantissas.
3. Add or subtract mantissas
4. Produce the result.

Registers are used for storing the intermediate results between the above operations.

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Instruction Pipeline

In this a stream of instructions can be executed by overlapping fetch, decode and execute phases of an instruction cycle. This type of technique is used to increase the throughput of the computer system.

An instruction pipeline reads instruction from the memory while previous instructions are being executed in other segments of the pipeline. Thus we can execute multiple instructions simultaneously. The pipeline will be more efficient if the instruction cycle is divided into segments of equal duration.

Advantages of Pipelining

1. The cycle time of the processor is reduced.
2. It increases the throughput of the system
3. It makes the system reliable.

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Disadvantages of Pipelining

1. The design of pipelined processor is complex and costly to manufacture.
2. The instruction latency is more.

ARM PROCESSING

        The ARM architecture was originally developed by Acorn Computers in the 1980s.

  An ARM processor is a specific type of computer processor designed according to a model developed by ARM holdings PLC. 

An ARM processor is one of a family of CPUs based on the RISC (reduced instruction set computer) architecture developed by Advanced RISC Machines (ARM).

ARM makes 32-bit and 64-bit RISC multi-core processors. RISC processors are designed to perform a smaller number of types of computer instructions so that they can operate at a higher speed, performing more millions of instructions per second (MIPS).  By stripping out unneeded instructions and optimizing pathways, RISC processors provide outstanding performance at a fraction of the power demand of CISC (complex instruction set computing) devices.

ARM processor features include:

• Load/store architecture.

• An orthogonal instruction set.

• Mostly single-cycle execution.

• Enhanced power-saving design.

• 64 and 32-bit execution states for scalable high performance.

• Hardware virtualization support.

      ARM processors are extensively used in consumer electronic devices such as smartphones, tablets, multimedia players and other mobile devices, such as wearables. Because of their reduced instruction set, they require fewer transistors, which enables a smaller die size for the integrated circuitry (IC).

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