Overview of embedded system 2- composition and application of embedded system

 

1. Composition of embedded system

         An embedded system device usually consists of Embedded computer system And actuator , Embedded computer system is the core of the whole embedded system , By hardware layer 、 Middle layer 、 System software layer and Application software layers . The actuator is also called controlled object , It's acceptable Embedded computer system Issued control command , Perform specified operations or tasks . The actuator can be very simple , Like a micro motor on a mobile phone , Turn on when the phone is in vibration receiving state ; It can also be complicated , Such as SONY intelligence Robot dog , It integrates a number of miniature control motors and a variety of sensor , Thus, it can perform various complex actions and feel various state information .

1． Hardware layer

The hardware layer contains Embedded microprocessors 、 Memory 、 General equipment interface and I/O Interface （A/D、D/A、I/O etc. ）. In one piece Embedded processor Add power supply on the basis of circuit 、 Clock circuit and Memory circuit , It constitutes an embedded core control module , That is, the minimum system . among operating system and Applications Can be solidified in the memory .

（1） Embedded microprocessors

         The core of embedded system hardware layer is Embedded microprocessors , Embedded microprocessor and general purpose processor CPU The biggest difference is that most embedded microprocessors work in systems specially designed for specific user groups , It will be universal CPU Many by card The completed tasks are integrated into the chip , Thus, it is conducive to the miniaturization of embedded system in design , At the same time, it also has a high efficiency And reliability .

Embedded microprocessors Of Architecture May adopt feng · Neumann System or Harvard architecture ; Command system You can choose a reduced instruction system （Reduced Instruction Set Computer,RISC） And complex instruction systems CISC（Complex Instruction Set Computer,CISC）.RISC The computer contains only the most useful instructions in the channel , Ensure that the data channel executes each instruction quickly , Thus, the execution efficiency And make CPU The hardware structure design becomes simpler .

Embedded microprocessors There are different systems , Even in the same system, there may be different clock frequency and Data bus width , Or integrate different peripherals and interfaces . according to an uncompleted statistic , Now the world Embedded microprocessors Has more than 1000 Varied , Architecture Yes 30 Multiple series , The mainstream systems are ARM、MIPS、Power PC、X86 etc. . But with the global PC The difference in the market is , There is no one Embedded microprocessors Can dominate the market , Only with 32 In terms of a product , There is 100 More than embedded microprocessors . Embedded microprocessors The choice of is based on the specific application .

（2） Memory

Embedded systems need Memory To store and execute code , Can be located in Microprocessor Inside or outside of , Its Capacity by 256KB~1GB, Depending on the specific application , General film Memory Small capacity , Fast , slice External memory Large capacity .

Commonly used as main memory Memory Yes ：

ROM class NOR Flash、EPROM and PROM etc. .

RAM class SRAM、DRAM and SDRAM etc. .

among NOR Flash With its many erasable times 、 Fast storage 、 Large storage capacity 、 Advantages such as low price , It has been widely used in the embedded field .

（3） General equipment interface and I/O Interface

The interaction between embedded system and the outside world requires a certain form of general equipment interface , Such as A/D、D/A、I/O etc. , Peripherals are connected to other off chip devices or sensors Microprocessor The input of / Output function . Each peripheral usually has only a single function , It can be outside the chip or built into the chip . There are many kinds of peripherals , From a simple serial communication device to a very complex wireless device .

At present, the common device interfaces in embedded systems are A/D（ model / Data conversion interface ）、D/A（ Count / Analog to digital converter ）,I/O Interface with RS-232 Interface （ serial communication Interface ）、Ethernet（ Ethernet Interface ）、USB（ Universal serial bus Interface ）、 Audio interface 、VGA Video output interface 、I2C（ field bus ）、SPI（ Serial peripheral interface ） and IrDA（ Infrared interface ） etc. .

2． Middle layer

The middle layer is between the hardware layer and the software layer , Also known as the hardware abstraction layer （Hardware Abstract Layer,HAL） or Board level support package （Board Support Package,BSP）, It separates the upper software from the lower hardware , Make the bottom layer of the system The driver Hardware independent , The upper software developers do not need to care about the specific situation of the underlying hardware , according to BSP The interface provided by layer can be developed . This layer generally contains initialization of related underlying hardware 、 Data input / Output operation and configuration function of hardware device .BSP It has the following two characteristics .

Hardware dependency ： because Embedded real time system Of Hardware environment It has application relevance , As the interface between upper software and hardware platform ,BSP Need to be for operating system Provide methods for operating and controlling specific hardware .

operating system The correlation ： Different operating systems have their own software hierarchy , therefore , Different operating systems have specific hardware interface forms .

actually ,BSP It's a gap between operating system And the underlying hardware , It includes most of the software modules which are closely related to hardware in the system . Design a complete BSP Two parts need to be completed ： Hardware initialization of embedded system and BSP function , Design hardware related Device drivers .

（1） Embedded system hardware initialization

System initialization The process can be divided into 3 The main link , From the bottom up 、 The order from hardware to software is ： Chip level initialization 、 Board level initialization and system level initialization .

Chip level initialization ： complete Embedded microprocessors The initialization , Including setting the core of embedded microprocessor register and Control register 、 The core working mode of embedded microprocessor and the design of embedded microprocessor Local bus Patterns, etc . Chip level initialization Embedded microprocessors From the default state at power on to the working state required by the system . This is a pure hardware initialization process .

Board level initialization ： complete Embedded microprocessors Initialization of other hardware devices . in addition , It is also necessary to set the data structure and parameters of some software , For subsequent system level initialization and Applications The running setup hardware and Software environment . This is an initialization process including both software and hardware .

System initialization ： The initialization process is mainly software initialization , Mainly on operating system The initialization .BSP Will be right Embedded microprocessors Control of is transferred to Embedded operating system , The operating system completes the remaining initialization operations , Includes loading and initializing hardware independent device drivers , establish system memory District , Load and initialize other system software modules , Such as network system 、 File system, etc . Last , operating system establish Applications Environmental Science , And give control to the entry of the application .

（2） Hardware related equipment The driver

BSP Another main function of is hardware related device driver . The initialization of hardware related device drivers is usually a process from high to low . Even though BSP Contains hardware related device drivers , However, these device drivers are usually not directly controlled by BSP Use , Instead, the system is initialized by BSP Put them with operating system And device drivers in general , And in the subsequent application, it is called by the general device driver , Realize the operation of hardware devices . Hardware related drivers are BSP Another key link in design and development .

3． System software layer

The system software layer consists of Real time multitasking operating system （Real-time Operation System,RTOS）、 file system 、 graphics The user interface （Graphic User Interface,GUI）、 Network system and general component module composition .RTOS It's embedded Application software The foundation and development platform of .

Embedded operating system （Embedded Operation System,EOS） It is a kind of widely used system software , In the past, it was mainly used in the fields of industrial control and defense system .EOS be responsible for Embedded systems All soft 、 Allocation of hardware resources 、 Task scheduling , control 、 Coordinate concurrent activities . It has to embody the characteristics of the system it is in , By loading and unloading some modules to achieve the functions required by the system . at present , Some successful applications have been launched EOS Product line . With Internet technology The development of 、 The popularization and application of information appliances EOS Miniaturization and specialization of ,EOS It began to develop from a single weak function to a highly specialized strong function . Embedded operating system Real time efficiency in the system 、 Hardware dependencies 、 Software solidification and application specificity have prominent characteristics .EOS Is relative to the general operating system In terms of the , In addition to having the most basic functions of the general operating system , Such as task scheduling 、 Synchronization mechanism 、 Interrupt handling 、 File function, etc , There are also the following features ：

（1） Portability . open 、 Scalable Architecture .

（2） Strong real-time .EOS The real-time performance is generally strong , It can be used in various equipment control .

（3） Unified interface . Provide various device drive interfaces .

（4） It is easy to operate 、 Simple 、 Provide friendly graphics GUI, The graphical interface , Pursue easy to learn and easy to use .

（5） Provide powerful network functions , Support TCP/IP Agreement and other agreements , Provide TCP/UDP/IP/PPP Protocol support And unified MAC Access layer interface , Reserved interfaces for all kinds of mobile computing devices .

（6） Strong stability , Weak interactivity . Once the embedded system starts to run, it doesn't need too much user intervention , This is responsible for system management EOS With strong stability . Embedded operating system The user interface of generally does not provide operation commands , It passes through system call The command to User programs Provide services .

（7） Solidify the code . stay Embedded systems in , Embedded operating system and Application software It is solidified in the embedded system computer ROM in . auxiliary Memory Rarely used in embedded systems , therefore , Embedded operating system The file management function of should be able to be easily disassembled , And with all kinds of memory file systems .

（8） Better hardware adaptability , That is good portability .

4． Application software layer

The application software layer is composed of application programs developed based on real-time systems , It is used to realize the control function of the controlled object . The function layer is oriented to controlled objects and users , For the convenience of users , It is often necessary to provide a friendly man-machine interface . For some complex systems , In the early stage of system design, the requirements of the system should be analyzed , Determine the function of the system , Then the functions of the system are mapped to the hardware of the whole system 、 During the design of software and execution device , It is called the functional realization of the system .

2 The application of embedded system

Embedded system technology is widely used , Pictured 1.1 Shown , It mainly includes the following aspects ：

The main application fields of the in-line system

（1） Industrial control

The industrial automation equipment based on embedded chip will get great development , There are already a lot of 8、16、32 Bit embedded microcontroller in application , Networking is to improve production efficiency And product quality 、 The main way to reduce human resources , Such as industrial process control 、 Digital machine tools 、 Electric power system 、 Power grid security 、 Power grid equipment monitoring 、 Petrochemical system . In terms of traditional industrial control products , Low end models tend to use 8 position Single chip microcomputer . But with the development of technology ,32 position 、64 Bit processor Gradually become the core of industrial control equipment , In the next few years, it will get great development .

（2） traffic control

In the vehicle navigation 、 flow control 、 Information monitoring and automobile service , Embedded system technology has been widely used , Embedded GPS modular ,GSM Mobile positioning of modules terminal It has been successfully used in various transportation industries . at present GPS Equipment has entered ordinary people's homes from cutting-edge products , Just a few thousand dollars , You can find your place anytime, anywhere .

（3） Information appliances

This will be called the biggest application area of embedded system , The refrigerator 、 Air conditioner And so on 、 Intelligence will lead people's life into a new space . Even if you're not at home , You can also use the phone line 、 Online Remote control . In these devices , Embedded system will be of great use .

（4） Home intelligent management system

water 、 electric 、 Remote control of gas meter Automatic meter reading , Safety and fire prevention 、 Anti theft system , The embedded special control chip will replace the traditional manual inspection , And achieve higher , More accurate and safer performance . At present, in the service field , For example, remote ordering device has already reflected the advantages of embedded system .

（5）POS Internet and e-commerce

Public transport contactless smart card (Contactless Smartcard, CSC) Distribution system , Public phone card distribution system , vending machine , All kinds of intelligence ATM The terminal will enter people's life in an all-round way , By then, you can travel all over the world with a card .

（6） Environmental engineering and nature

Real time monitoring of hydrological data , Flood control system and water and soil quality monitoring 、 Dam safety , Earthquake monitoring network , Real time meteorological information network , Water and air pollution monitoring . In a lot of bad environments , A complex area , The embedded monitoring system will be implemented .

（7） National defense and aerospace

The development of embedded chips will make robot In miniaturization , The advantage of high intelligence is more obvious , At the same time, it will greatly reduce the price of robots , It is widely used in industry and service fields .

Several specific application examples ：

Remote appliance control , In addition to developing support TCP/IP Embedded systems , The control agreement of household appliances also needs to be formulated and unified , This needs home appliance manufacturers to do . Same thing , All network-based remote controller devices need to implement interfaces with embedded systems , Then, it is controlled by the embedded system through The Internet Achieve control . therefore , It is of great significance to develop and discuss the embedded system .

Based on embedded system in power grid remote monitoring , It can realize the active measurement of power grid parameters 、 analysis 、 Automatic storage and other functions , adopt Internet The optical fiber ring network transmits the power grid monitoring data to the monitoring host in the dispatching room , The staff can timely monitor the operation status of the remote equipment 、 Accurate monitoring , Judge and predict the fault precursor , Take effective measures to solve problems , Ensure the safe operation of large units , Prevent the occurrence of malignant accidents , Avoid the production pause caused by regular maintenance , It can prevent and eliminate faults , Improve the reliability of equipment operation 、 Safety and effectiveness .

Based on embedded system RFID Handset system , With ARM tiny processor Master controller , According to the requirements of the system SRAM、Flash、SD card 、 keyboard 、LCD Show 、 Sound prompt for data processing 、 data storage 、 Human computer interaction and error alarm prompt , adopt USB The interface can communicate with the host , The backlight module can be LCD and keyboard Provide backlight , The voltage detection module passes through the core processor A/D The converter detects the battery voltage , Thus, the remaining power of the battery can be detected indirectly ,RF The module can transmit and receive RF signals between the reader and the tag , adopt JTAG Interface can debug and download programs . The power part can provide power for each module in the system that needs power .