Chapter 1 Embedded Real Time System Overview
1.1 Embedded System Overview
1.1.1 Historical Development of Embedded Technology
The emergence of embedded systems has been more than 30 years, and embedded technology has also passed several development phases. After entering the 1990s, the digital technology of computer and software has achieved rapid development, which not only extensively penetrates social economy, military, transportation, communications and other related industries, but also deep into home appliances, entertainment, art, social and cultural, etc. A digital technology revolution has been set off. Multimedia technology and Internet applications are rapidly popularized, consumptive electron, computer, communication, 3C integrated trend is increasing, and embedded techniques are once again a research hotspot. Occurving the development of embedded technology, the following four phases are generally experienced [1].
l The first phase is a system in the form of a programmable controller in a single chip, and has a function of mating with monitoring, servo, and instructing devices. Most of this system is applied to some professional industrial control systems. It is generally not supported by operating systems. The system is directly controlled by assembly language programming, and the memory is cleared after running. The main feature of this stage system is that the system structure and function are relatively single, low processing efficiency, small storage capacity, and there is almost no user interface. Since this embedded system is easy to use, the price is very low, it is more common in domestic industrial sector, but it has not been adapted to efficient and requires modern industrial control and emerging information home appliances in large-capacity storage media.
l The second phase is an embedded system based with an embedded CPU to a simple operating system as a core. The main features of this stage system are: a wide variety of CPUs, weak versatility; small system overhead, high efficiency; operating system has certain compatibility and scalability; application software is more professional, the user interface is not friendly; Control system load and monitor applications run.
l The third stage is an embedded system with an embedded operating system. The main feature of this stage system is that the embedded operating system can operate on a variety of different types of microprocessors, compatible; the operating system is kept, high efficiency, and high modular and scalability; Files and directory management, device support, multitasking, web support, graphics windows, and user interfaces; with a large number of application interface (APIs), develop applications simple; embedded application is rich.
l The fourth stage is an embedded system based on Internet-based, which is a rapid development phase. At present, most embedded systems are still outside the Internet, but with the development of the Internet and Internet technology and information appliances, industrial control technology, the combination of embedded equipment and Internet will represent the true future of embedded technology. .
1.1.2 Technical Features and Application Prospects of Embedded Systems
The embedded system is mainly composed of an embedded processor, a related support hardware, and an embedded software system, which is an independent "device" that is integrated with soft hardware. The embedded processor is mainly composed of a single chip or microcontroller (MCU). These embedded CPUs are currently 8-bit and 16-bit, compared to 32-bit or 64-bit high-performance processors, have strong economics and reality. Related support hardware includes display cards, storage media (ROM, and RAM, etc.), communication devices, IC cards, or credit card read devices, etc. The embedded system is different from the general computer processing system, which does not have a storage medium like a hard disk, and most of the flash memory is used as the storage medium. Embedded software includes underlying software, operating systems, graphics interfaces, communication protocols, database systems, standardized browsers, and application software, etc. related to hardware.
Overall, the embedded system has convenient and flexible, high performance ratio, strong embedded, and can be embedded in any information appliance and industrial control system. From a software point of view, the embedded system has an unharitable modification, and the system needs to be required to have a low systematic professionalism and real-time. The post-PC era is a real stage, and it is a forecast of the forecast. The embedded system is a product that is closely related to this era, which will close the distance from the computer to form a harmonious work and living environment. From a certain point of view, embedded systems can be applied to various fields of human work and life, with extremely vast application prospects. Embedded systems have extensive application space in traditional industrial control and commercial management, such as intelligent industrial control equipment, POS / ATM machine, IC card, etc .; more extensive application potential in the family, such as set-top boxes, digital TV, webtv Many consumer and health care electronic devices such as network refrigerators, cybers, etc. In addition, there are also applications in media mobile phones, pocket computers, handheld computers, car navigators, etc., will greatly promote embedded technology to life and work. Each side. It is also huge in entertainment and military application, and it is obvious to all.
1.1.3 Typical embedded system
Information appliance business opportunities trigger global embedded operating system platform, worldwide 4 major operating system camp Wince [18], Palm OS [19], EPOC [20] and Linux [21] Expand the specifications, each with software and hardware cooperative manufacturers compete Information home appliance market share.
The global handheld information applied home appliances rapidly, according to forecasts, the market growth rate will arrive at 77.4% in 2000, and the personal digital assistant mobile phone and other hand-held information appliance operating system competition is increasingly fierce. In addition to the new round of business opportunities, applications manufacturers include electronic dictionaries, electronic maps, and game developers, including electronic dictionaries, electronic maps, and game developers.
The Microsoft Window operating system has the advantage of operating system share on your computer, making Wince have strong window resource support. However, the Palm OS operating system has 70% of the global PDA products, and supports multinational companies such as 3COM, IBM and Sony. EPOC is a new operating system developed from the world's largest three mobile phone manufacturers from Nokia, Ericsson and Motorola, which is the world's largest, integrated into new company. Under the cooperation of 3 telephone manufacturers, The EPOC market has great potential and has high share, but the application function is based on mobile phones, and there is no open authorization.
In addition, Linux will also be a strong force in the future; due to Linux open source, through these years, it has become a robust and reliable high-performance operating system. The more and more embedded system designer finds Linux to be an excellent embedded operating system. The biggest advantage of Linux is that it is an open operating system. Due to Linux open source, everything of the operating system is transparent to the user, and users can maximize the progress and cost of system development. A wide variety of hardware devices encountered during the development process, which can easily find the drivers of these devices to get support. Linux built-in network support, users can easily make their embedded network features. Linux is a modular operating system that provides excellent scalable features that can easily delete unwanted modules, most embedded systems are very sensitive to the operating system, Linux can choose specific Function modules, independently build embedded operating systems. Linux supports the vast majority of CPUs, including Intel, MIPS, ASIC, Alpha, 68K, POWER PC, etc. This allows Linux to almost embedded on a variety of hardware devices. Become a strong development of various manufacturers, plus its core, and potential.
1.2 Real-time system overview
1.2.1 What is the real-time system real-time calculation is becoming an increasingly important principle. Operating systems, especially scheduling programs, may be the most important components in real-time systems. Examples of real-time systems include experimental control, process control equipment, robot, air traffic control, remote communication, military command and control system, next-generation system will also include automatic driving cars, robotic controllers with elastic joints, intelligent production System control, space station and subsea exploration, etc.
Real-time calculation [5] can be defined as a class of calculations, that is, the correctness of the system depends not only on the logical result of the calculation, but also depends on the time of generating results. We can define real-time systems by defining real-time processes or real-time tasks. Generally speaking, in a real-time system, some tasks are real-time tasks, which have a certain degree of urgency. Such tasks try to control events that have occurred outside the world or respond to events. Since these events occur "real-time", the real-time task must be able to keep up with the event it cares. Therefore, a deadline is usually developed to a particular task, and the deadline specifies the start time or end time. Such tasks can be divided into hard tasks or soft tasks. A hard real-time task refers to a limit that must meet the deadline, otherwise it will bring undesired damage or fatal errors to the system. A soft real-time task is also a final deadline associated with it, and hopes to meet the requirements of this period, but this is not forced, even more than the last deadline, scheduling and completing this task remains. meaningful. Another feature of real-time tasks is that they are cycles or non-cyclics. A non-periodic task has a deadline that must end or start, or has a constraint about the start time and end time. For Periodic Task, this requirement is described as "one cycle T once," or "every T unit".
1.2.2 Characteristics of real-time operating systems
Real-time operating systems generally meet the following requirements [5]:
l Determinability: means that it can perform operations in accordance with fixed, predetermined time or time intervals.
l Responsibility: means that the system is the time when the system is interrupted after the system is interrupted.
l User control: refers to the various attributes (task priority, task permissions, etc.) that allows users to finely control the task.
l Reliability
l Troubleshooting: means that the system will save its power and data as much as possible in the fault.
Embedded systems are generally real-time systems, and most of the real-time system is used in embedded environments. Real-time operating systems for embedded occasions are embedded real-time operating systems. In a relatively complete embedded system environment, you need an operating system (RTOS) kernel that supports real-time multitasking because embedded equipment widely used in the real world must have the ability to interact with external environments. RTOS is directly related to embedded application complications. Today, the complexity of application requirements is increasing today. If real-time application software is not based on a perfect RTOS, then the system software and application software cannot be separated, the development cycle is too long. And the cost is too high. Therefore, RTOS is an inevitable product developed in real time applications.
