Microcontroller and embedded, in fact, there is no standard definition to distinguish between them, for a single chip microcomputer and embedded development of developers, have their own definition, next, just talk about the understanding of these two concepts,

01
What is the single chip microcomputer

First clear concept, what is the single chip microcomputer, single chip microcomputer is A kind of integrated circuit chips, is to use very large scale integrated circuit technology with data processing ability of the central processor, the CPU, RAM RAM, read-only memory ROM, A variety of I/O mouth and interrupt system, timer/counter function (may include display driver circuit, pulse width modulation circuit, analog multiplexer and A/D converter circuit) such as integration to A piece of silicon consisting of A small and perfect microcomputer system, widely used in the field of industrial control,



Since the 1980 s, by the time of the four, 8-bit microcontroller, development to the present 300 m high speed single chip microcomputer, such as the classic 51 series microcontroller, appearance is just a piece of a thumb size cuboid chip, a total of 40 pin, contains the arithmetic logic unit, is actually a CPU,

In the first contact with single chip microcomputer, also had a question that why SCM is black and not the other can be a color, afterwards just know is single chip material limit,

For single chip microcomputer, in fact, a single chip is all, other such as single chip microcomputer minimum system is for the normal operation of MCU, such as crystals, 5 v power supply, inductor resistance, etc., of course can only ensure the normal operation of single chip microcomputer minimum system, almost not achieve any application based on single chip microcomputer,

In order to make the singlechip microcomputer application, must want to join other peripherals, such as buttons, led lamp, led screen, buzzer, all kinds of sensor, which is on the market a lot of companies are doing MCU development board,
Summary, microcontroller is complete operation, logic control, communications, and other functions of a single module, MCU true name is "single", DSP chip can also be regarded as a single chip microcomputer, and of course they performance is strong, but the function is still a single, anyhow is to process the data, logic,


02
What is an embedded

So what is embedded, the general said embedded is refers to the embedded system, the IEEE (InsTItuteof Electrical and ElectronicsEngineers, the American association of Electrical and electronics engineers) definition of embedded system: "is used to control, monitor or auxiliary operating machinery and equipment device",

Embedded system is a kind of special computer system, as part of a device or equipment, in general, the embedded system is a control program stored in the ROM is embedded processor control board,



Embedded system applications, operating systems, and computer hardware connected system, refers to the application as the center, on the basis of computer technology, software and hardware can be cut, for the user application to function, reliability, cost, volume, power consumption and the use of the environment have special requirements of special computer system,

In fact, all with a digital interface devices, such as watches, microwave ovens, video recorders, cars, etc., all with an embedded system, some embedded system also includes the operating system, but most of the embedded system is controlled by a single program to realize the whole logic, this is because the embedded system is commonly used in industrial control, that is to say foreign set control is write die, does not need manual intervention, also in order to keep the system stable and reliable,

We can often hear the company recruitment requirements is an embedded software engineer or embedded hardware engineer, that is to say, the embedded system including software and hardware, actually think carefully can understand, all have already run system, of course, there are also software BSP hardware,

That is an embedded system is a combination of software and hardware, and generally recognized by the domestic embedded system is defined as: to apply as the center, on the basis of computer technology, software and hardware can be cut, to adapt to the application system for function, reliability, cost, volume, power consumption and so on a special computer system, strict


03
Embedded hardware layer

Hardware layer contains embedded microcontroller processor, memory (SDRAM, ROM, Flash, etc.), general device interface and I/O interface (A/D, D/A, I/O, etc.), based on an embedded processor to add power supply circuit, clocking circuit and memory circuit, constitutes A embedded core control module, including operating systems and applications can be cured in ROM,

One of the core is microprocessor, embedded processors and general computer CPU and distinction, embedded microcontroller processor mostly work in the specific design of the system, such as TI or Atmel company has many different processors, Atmel SAM series is specially designed for the Internet of things, AVR is due to the outstanding performance, widely used in industrial field,

Embedded microcontroller processor has a variety of different systems, even in the same system may have a different clock frequency and data bus width, or integrates different peripherals and interfaces, according to incomplete statistics, the embedded microcontroller processor has more than 1000 kinds of the world, architecture has more than 30 series, one of the mainstream system with ARM, MIPS, PowerPC, X86 and SH, etc.,

But, unlike the global PC market without an embedded microcontroller processor can dominate the market, with only a 32-bit products, has more than 100 kinds of embedded microcontroller processor, embedded microcontroller processor choice is determined according to the specific application,



In embedded field, it can be said that the ARM architecture processor occupied half of the ARM has become a famous company of science and technology, and it did not produce any processor, but only provides the IP, it can be seen leading companies do standards, while others use more architecture is MIPS, Sparc, powerpc,

ARM, for example, there are all kinds of processor architecture that most classic architecture series, it belongs to ARMv7 architecture, it is until 2010 ARM instruction set architecture, latest ARMv7 architecture defines three series, A clear division of responsibilities: "A" series of cutting-edge oriented based on the operation of the virtual memory system and user application;" R series for real-time systems; "" M "series of microcontrollers,

Embedded systems and external interaction need some form of universal interface equipment, such as A/D, D/A, such as I/O, peripherals through and piece of other devices or sensors connected to realize the function of the input/output of the microprocessor, each peripherals are usually only A single function, it can be outside the chip built-in chip, many different kinds of peripherals, from A simple serial communication equipment to very complex 802.11 wireless devices,

Embedded system that is commonly used in general equipment interface has A/D (D/A conversion interface), D/A (conversion interface/A), I/O interface with RS - 232 interface (serial communication interface), Ethernet interface (Ethernet), USB (universal serial bus (USB) interface), audio interface, VGA video output interface, the I2C (fieldbus), SPI (serial peripheral interface) and IrDA infrared interface (), etc., this is similar to single chip microcomputer,


04
Embedded software layer

Also is the operating system, including the kernel and file system, and more on top of application, embedded operating system is Linux or other unix-like commonly, there are also some real-time operating system (RTOS) such as VxWorks, RTEMS, ucOS,

One Linux includes different distribuTIon, such as Ubuntu, Redhat, Debian, centos, etc., all of them are using the Linux kernel, the difference is the software and tools, don't need to worry too much about the standard question, too, of course, these are almost all Linux distributions selected software are universal, such as Apache web server, E-mail server postfix, sendmail, Samba file server, etc., in addition to standards such as Linuxstandard base to standardize developers, unix-like mainly FreeBSD and Solaris,



Embedded real-time operating system, is one of the most commonly used in the field of the core of the real-time operating system is real-time, nature is the predictability of the time it takes to task processing, namely the task need to be made within the prescribed time limit, the IEEE for real-time system is defined as "the correctness depends not only on the logical result also depends on the results of the calculation system" for the time involved,

Real-time operating system with hard real-time and soft real-time and hard real-time requirements within the prescribed time, must complete the operation, it is in the operating system when the design guarantee; Soft real-time, as long as according to the priority of task can be completed as soon as possible, we usually use the operating system after a certain change can become a real-time operating system,

Real-time operating system and Linux the time-sharing operating system difference is listed as follows:

(1) multiple sex, as well as real-time information processing system and time-sharing multiplexing, system according to the principle to serve multiple end users; And the real-time control system, its multiple sex is mainly manifested in the site frequently to the multiplex information collection and to control more than one object or multiple actuators,

(2) the independence, as well as real-time information processing system and time-sharing system independence, each end user when asked time-sharing system service request, is independent of each other, each other; In real-time control system of information collection and control of the object, also each other noninterference,

(3) the timeliness, real-time information systems and time-sharing system similar to the requirement of real-time performance, are the waiting time of people can accept to determine; And the timeliness of real-time control system, it is required by the control object to start deadline or completion deadline to determine, for the second stage, the millisecond until millisecond, even some less than 100 microseconds,

(4) interactivity, real-time interactive information processing system, but here people interaction with the system, limited to access the system in a certain special service program, it is not like a time-sharing system can provide data processing services to end users, resource sharing and so on service,

(5) reliability, time-sharing system requirements and reliable, by contrast, real-time systems require highly reliable, since any mistake could bring huge economic losses and even cannot predict disastrous consequences, therefore, in a real-time system, multi-level fault-tolerant measures were taken to ensure the safety of the system and data security,

Due to more reliable and timely, embedded real-time operating system is more widely used in industrial control, aerospace, military industry and other fields, such as the U.S. space agency NASA launched in recent years, such as Mars probe is made of RTEMS real-time operating system,


05
Embedded in the middle tier

So-called middle layer is the layer of software and hardware interfaces between layers, but strictly speaking also belong to the software layer, general developers call BSP, this layer is mainly responsible for the downward provide hardware driver, the hardware configuration such as operation, and to the software developers to provide standard API, to develop the middle tier developers often referred to as embedded driver engineers,



Can also be seen from here, embedded design and softness are inseparable, both to grasp the characteristics of the underlying hardware and how to drive their work, also want to understand relevant knowledge of the operating system, can write the corresponding function of application,
So to see if an operating system supports a chip or a development board, just by looking at its source code included in the corresponding chip level or development board of the board support package,


06
Embedded system should run in what kind of hardware

About embedded hardware or development board, I think many people the first impression is RaspberryPi, only the size of a credit card is a miniature computer, although it looks "small", the "core" is very powerful, video, audio, etc all have, is "the sparrow is small, all-sided", raspberry pie after launch, a lot of manufacturers to launch similar products, such as banana pie, such as

And TI Beagleboneblack boards, size and raspberry pie, peripherals including USB host and mini USB and network interface, and an sd card slot on the back and the HDMI interface, BBB processor is currently the most popular embedded systems ARMv7 instruction set, using the instruction set processor can be widely used today more and more software support, for example, some operating system is not support run on ARMv6 instruction set, for example, Ubuntu in April 2012 abandoned support for ARMv6 instruction set,

Relative and ARMv6 ARMv7 instruction set another advantage is that use more strong, the actual performance of the ARMv7 processor ARMv7 relative to still have a lot of advantages and ARMv6, such as some notable improvements: the superscalar architecture, contains the SIMD instructions, improved the branch so as to greatly improve the performance of some prediction algorithms,


07
Conclusion

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