Android Deep Exploration with Hal Drive Development (Vol. 1)--fifth chapter essay

RISC (reduced instruction set computer) compact instruction set computer

Brief introduction

The simplified instruction set is a design mode of the computer's central processing unit, also known as RISC (reduced instruction set computer abbreviation). [1] This design approach to the number of instructions and addressing methods have been streamlined to make it easier to implement, the instruction parallel execution degree is better, the compiler more efficient. Commonly used simplified instruction set microprocessors include DECAlpha, ARC, ARM, AVR, MIPS, Pa-risc, powerarchitecture (including PowerPC), and SPARC. This design idea originated from the discovery that, although traditional processors have designed many features to make code easier to write, these complex features require several instruction cycles to be implemented and are often not used by running programs. In addition, the difference between the speed of the processor and the main memory is becoming larger. These factors led to the emergence of a series of new technologies that allow the processor's instructions to be executed in a running stream while reducing the number of times the processor accesses memory. In the early days, this instruction set was characterized by a small number of instructions, each with a standard word length, a short execution time, and the implementation details of the CPU are visible to machine-level programs.

Development prospects

In view of the design features of RISC and its incomparable advantages, the development direction of RISC architecture processor is as follows:
One is to increase the parallelism of the processor;
The second is to extend the function of supporting the scalable parallel computer system;
Third, improve the level of technology. Finally RISC and DSP in the embedded application of the perfect integration, inseparable.
RISC microprocessors not only simplify the instruction system, use superscalar and ultra-pipelined structure, their instruction number only dozens of, but greatly enhance the parallel processing capability. such as: 1987 Sunmicrosystem Company introduced the SPARC chip is a superscalar structure of RISC processor. The MIPS processors introduced by SGI use the ultra-pipelined architecture, which plays a central role in building parallel streamlined instruction system multiprocessor. RISC processor is the mainstream chip of 64-bit multiprocessor in UNIX field today.

Performance features

One: Because the instruction set simplifies, the pipeline and the common instruction all can use the hardware execution;
Second: The use of a large number of registers, so that most of the instruction operation is between the registers, improve the processing speed;
Three: The use of Cache-host-external memory three storage structure, so that the number of numbers and the number of memory instructions to execute, so that the processor can do as much work as possible, and not because of the memory access information and slow processing speed.

Application features

Because RISC processor instruction is simple, the use of hard wiring control logic, processing power, fast, the world's most UNIX workstations and server manufacturers are using RISC chip for CPU. such as the original Dec Alpha21364, IBM's PowerPCG4, HP PA-8900, SGI r12000a and Sunmicrosystem company.

Operating features

RISC chips typically operate at 400MHZ orders of magnitude. The clock frequency is low, the power consumes less, the temperature rises also is few, the machine is not easy to fail and the aging, improves the system reliability. A single instruction cycle accommodates multiple parallel operations. In the development process of RISC microprocessors. Has produced the ultra-long instruction Word (VLIW) microprocessor, which uses a very long set of instructions to link many instructions together to be executed in parallel. The basic model of the VLIW processor is the execution model of the scalar code, so that there are multiple operations within each machine cycle. Some RISC processors also use a few VLIW instructions to improve processing speed.

Android Deep Exploration with Hal Drive Development (Vol. 1)--fifth chapter essay