Discuss and compare various embedded micro-controller core like RISC, CISC, SOC, ARM.

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Comparison of RISC and CISC

Properties	RISC	CISC
Number of Instructions	Less	More
---	---	---
Addressing Modes	Less	More
Instruction Formats	Less	More
Instruction Size	Fixed	Variable
Control Unit	Hardwired	Micro-programmed
Number of Bus Cycles to execute an instruction	Single CPU cycle (for 80% Instructions)	Multiple CPU cycles
Control Logic And Decoding Subsystem	Simple	Complex
Pipelining	Huge no. of stages of Pipelining	Difficulty in efficient implementation
Design time and Probability of Design Errors	Smaller time and less probable	Long time and Significant probability
Complexity of Compiler	Simpler	More complex and the results of “optimization” may not be most efficient and the fastest machine language code
HLL instructions	Supported	Not Supported

ARM Microcontroller Core

ARM is the industry’s leading provider of 32-bit embedded RISC microprocessors with almost 75% of the market. ARM offers a wide range of processor cores based on a common architecture and delivering high performance together with low power consumption and system cost.

The ARM processor range provides solutions for :

Open platforms running complex operating systems for wireless, consumer and imaging applications.
Embedded real-time systems for mass storage, automotive, industrial and networking applications.
Secure applications including smart cards and SIMs.

The ARM architecture incorporated a number of features from RISC design like:

A load-store architecture

A load-store architecture means that ALU instructions cannot access memory, they can operate only on registers. Data transfer between memory and processor is possible only by Load and Store instructions.
LOAD instruction is used to load the data from memory into the processor’s register.
STORE instruction is used to store data in memory from the processor’s register.
The data in the registers can be processed by the ALU.

Fixed-length 32-bit instructions

All the instructions are 32-bit in length.
This fixed length instructions make the design of the control unit simpler.
Fixed length instructions also make it possible to use Hardwired control unit, which makes the operation of control unit faster.

3-address instruction formats

This is also referred to as 3-opeand instructions
The two source operands are different than the destination operand for e.g. in the add instruction given below
ADDd, s1, s2 ; Operation of above instruction:d := s1 + s2

f bits	n bits	n bits	n bits
function	Op 1 addr.	Op 2 addr.	Dest. Addr.

Fig.: A 3-address instruction format.

Simplicity:

The combination of the simple hardware with an instruction set that is grounded in RISC ideas but retains a few key CISC features, and thereby achieves a significantly better code density than a pure RISC, has given the ARM its power-efficiency and its small core size. This simplicity gives

A high instruction throughput
An excellent real time interrupt response
A small and cost effective processor

SOC:

A SOC may be embedded with the following components:

Embedded processor that may be General Purpose Processor (GPP) or Application Specific Instruction set Processor (ASIP)
Single purpose processing core or multiple processor cores
A network bus protocol implementing core
An encryption unit
Signal processing unit
Field Programmable Gate Array (FPGA) to implement some logical circuit
Memory
Analog units

One of the widely used place for SOC is mobile phones. Single purpose processors are configured for dialing, modulating, demodulating, deciphering, interfacing keypad and multi line LCD or graphic LCD, touch screen, storing data.

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