Elements of Embedded System

1. Hardware: Core element of an embedded system is the processor or a computational unit. Processors can act as brain of the system. They can be programmed to do perform a task. This can be designed using variety of options.

2. General Purpose Microprocessor: General purpose microprocessors are single-chip semiconductor device which is a computer on chip, but not a complete computer. Its CPU contains an Arithmetic & Logic Unit (ALU), a Program Counter (PC), a Stack Pointer (SP), registers, a clock and interrupts circuit on a single chip. To make complete microcomputer, one must add memory usually ROM and RAM, memory decoder, an oscillator, a number of serial and parallel ports.

A general-purpose processor is designed to cater for large amount of applications and hence is produced in bulk. Using it in an embedded system offers various benefits. Design time is low as only software is to be developed, no digital design is involved. Typical characteristics of a general purpose processors are relatively high cost, high speeds, higher Power consumption, large architecture, large memory size, onboard flash and cache, an external bus interface for greater memory usage.

3. Embedded Processors: A micro-controller is a functional computer system on a chip. It contains an integrated processor, memory, several peripheral devices, such as timers, analog to digital converters and serial communication devices all on one chip resulting in compact and low-power implementations. It is not expandable as it has no external bus interface.

Example: PICs DSPIC33/PIC24, Motorola 6811, Intel’s 8051.

Microcontrollers provide pin access which allows programs to easily monitor sensors, set actuators and transfer data with other devices. Providing specialized instructions improves performance for embedded systems applications. Thus, micro-controllers can be considered ASIPs to some degree. Special micro-controllers are often called embedded processors.

4. ASIP/DSPs: An application-specific instruction-set processor (ASIP) is designed for a specific class of applications with common characteristics, such as digital-signal processing, telecommunications, embedded control, etc. Using an ASIP in an embedded system can provide the benefit of flexibility while still achieving good performance, power and size. However, such processors can require large Non-Recurring Engineering (NRE) cost. Digital-Signal Processors (DSPs) are a common class of ASIP. DSP is a single-chip VLSI unit, a processor designed specially to support high-performance, repetitive numerically intensive tasks, including operations like multiply and add or shift and add.

Typically features of DSP processors are:
1. Harvard Architecture
2. MAC Unit to support Multiply-Accumulate Operations in a single cycle.
3. Ability to complete several accesses to memory in a single instruction cycle.
4. One or more dedicated address generation units to speed up arithmetic processing.

Example: TMS320Cxx, SHARC, and Motorola 5600xx.

5. ASICs: ICs are basically “chips”, Silicon Wafers with transistors, resistors, capacitors fabricated to act as Microprocessors, Amplifier, Memory, etc. ASICs (Application Specific Integrated Circuits) are designed for a special application. Digital to Audio Converter, DSSS receiver, MPEG-2 Decoder are examples of ASICs. It offers very high-performance, but NRE cost is very high. With ASICs timing closure is an issue especially with Submicroscopic geometric s. Re-configuration is highly limited.

6. FPGA/CPLDs: Field Programmable Gate Array (FPGA) is a fully programmable alternative to a customized chip. They are also called Reconfigurable Processing Unit. It is a two dimensional array of logic blocks & function of each block. FPGA technology allows you to embed a processor, ROM, RAM, DSP and any other block onto a single chip. This is replacing parallel hardware with the flexibility of the software. This has major advantages in terms of cost, reliability, re-usability of intellectual property and time to market.

7. Reconfiguration SoCs: Technological evolution particularly shrinking silicon fabrication geometric s is enabling the integration of complex platforms in a single system on a chip (SoC). In addition to specific hardware subsystems, a modern SoC also can include one or several CPU subsystems to execute software and sophisticated interconnects. Multimedia platforms such as Nomadik and Nexperia are examples of multiprocessor SoC that use digital signal processors, micro-controllers and other kinds of programmable processors.