RASPBERRY PI BASED SYSTEMS

Embedded systems are a cornerstone of the electronics industry today.
An embedded system is a computer or processor based system that has been designed for a specific purpose.

The system gains its name from the fact that the software is embedded into it for a particular application. The embedded system is not like a PC or other computer that can run a variety of programmes and fulfil a whole host of tasks.
The item using an embedded system is designed for a specific task and has its software preloaded, although updates may be undertaken from time to time.

Embedded systems basics

It may be asked what is an embedded system. With many processor based systems and computers it is useful to define what an embedded system is. A convenient definition for an embedded system is An embedded system is any computer system contained within a product that is not described as a computer.
Using this embedded system definition it is possible to understand the various basic characteristics one. Typically they are:

• Embedded systems are designed for a specific task. Although they use computer techniques, they cannot be used as a general purpose computer using a variety of different programmes for different task. In this way their function can be focussed onto what they need to do, and they can accordingly be made cheaper and more efficiently.
• The software for embedded systems is normally referred to as firmware. Rather than being stored on a disc, where many programmes can be stored, the single programme for an embedded system is normally stored on chip and it is referred to as firmware.

Embedded systems contain two main elements

• Embedded system hardware: As with any electronic system, an embedded system requires a hardware platform on which to run. The hardware will be based around a microprocessor or microcontroller. The embedded system hardware will also contain other elements including memory, input output (I/O) interfaces as well as the user interface, and the display.
• Embedded system software: The embedded system software is written to perform a particular function. It is typically written in a high level format and then compiled down to provide code that can be lodged within a non-volatile memory within the hardware.

Embedded Processor Hardware

• Embedded systems basics
• Embedded processor hardware
• CPU
• Embedded MPU
• Embedded MCU
• RAM

When developing an embedded system, one of the options is to base the computational hardware around a microcontroller, MCU rather than a microprocessor, MPU.

Both approaches have their attractions, but generally they will be found in different applications. Typically the microcontroller, MCU, is found in applications where size, low power and low cost are key requirements.

The MCU, microcontroller is different to a microprocessor in that it contains more elements of the overall processing engine within the one chip.

Bringing most of the processing engine components onto a single chip reduces size and cost. This enables it to become economical viable to digitally control even more devices and processes. Also it is found that mixed signal microcontrollers are being increasingly used, integrating analogue components needed to control non-digital electronic systems.

Microcontroller basics

Microcontrollers comprise the main elements of a small computer system on a single chip. They contain the memory, and IO as well as the CPU one the same chip. This considerably reduces the size, making them ideal for small embedded systems, but means that there are compromises in terms of performance and flexibility.

As microcontrollers are often intended for low power and low processing applications, some microcontrollers may only use 4 bit words and they may also operate with very low clock rates - some 10 kHz and less to conserve power. This means that some MCUs may only consume a milli watt or so and they may also have sleep consumption levels of a few nano watts. At the other end of the scale some MCUs may need much higher levels of performance and may have very much higher clock speeds and power consumption.

Different types of Microcontrollers

1. 8051
2. ARM
3. PIC
4. Arduino
5. AVR

Functions	8051	PIC	AVR	ARM
Bus width	8-bit for standard core	8/16/32-bit	8/32-bit	32-bit mostly also available in 64-bit
Communication Protocols	UART, USART,SPI,I2C	PIC, UART, USART, LIN, CAN, Ethernet, SPI, I2S	UART, USART, SPI, I2C, (special purpose AVR support CAN, USB, Ethernet)	UART, USART, LIN, I2C, SPI, CAN, USB, Ethernet, I2S, DSP, SAI (serial audio interface), IrDA
Speed	12 Clock/instruction cycle	4 Clock/instruction cycle	1 clock/ instruction cycle	1 clock/ instruction cycle
Memory	ROM, SRAM, FLASH	SRAM, FLASH	Flash, SRAM, EEPROM	Flash, SDRAM, EEPROM
ISA	CLSC	Some feature of RISC	RISC	RISC
Memory Architecture	Von Neumann architecture	Harvard architecture	Modified	Modified Harvard architecture
Power Consumption	Average	Low	Low	Low
Families	8051 variants	PIC16,PIC17, PIC18, PIC24, PIC32	Tiny, Atmega, Xmega, special purpose AVR	ARMv4,5,6,7 and series
Community	Vast	Very Good	Very Good	Vast
Manufacturer	NXP, Atmel, Silicon Labs, Dallas, Cyprus, Infineon, etc.	Microchip Average	Atmel	Apple, Nvidia, Qualcomm, Samsung Electronics, and TI etc.
Cost (as compared to features provide)	Very Low	Average	Average	Low
Other Feature	Known for its Standard	Cheap	Cheap, effective	High speed operation Vast
Popular Microcontrollers	AT89C51, P89v51, etc.	PIC18fXX8, PIC16f88X, PIC32MXX	Atmega8, 16, 32, Arduino Community	LPC2148, ARM Cortex-M0 to ARM Cortex-M7, etc.