With the development of electronic information science and technology towards informatization, intelligence, and networking, microcontrollers and embedded systems have gained extensive application space. This article briefly analyzes the connections and structural comparisons between microcontrollers and embedded systems, and lists several embedded real-time operating systems suitable for the PIC18F series microcontrollers.
Comparison of the Structural Composition of Microcontrollers and Embedded Systems
(1) Basic Structure of Microcontrollers
A microcontroller consists of an arithmetic unit, a controller, memory, and input/output devices.
(2) Components of Embedded Systems:
Embedded systems generally consist of the following groups: embedded microprocessors, peripheral hardware devices, embedded operating systems, and specific application programs.
The first step in embedded system design is to combine specific applications, comprehensively consider the system’s requirements for cost, performance, scalability, development cycle, and other aspects, determine the main control device of the system, and build the system hardware platform around it.
Connections Between Microcontrollers and Embedded Systems
A microcontroller is an integrated circuit chip that uses very large scale integration (VLSI) technology to integrate a central processing unit (CPU) with data processing capabilities, random access memory (RAM), read-only memory (ROM), various I/O ports, an interrupt system, timers/counters, and other functions (which may also include display driver circuits, pulse width modulation circuits, analog multiplexers, A/D converters, etc.) into a small and complete microcomputer system on a single silicon chip, widely used in the industrial control field. Since the 1980s, microcontrollers have evolved from 4-bit and 8-bit microcontrollers to today’s 32-bit 300M high-speed microcontrollers.
The earliest microcontroller was Intel’s 8048, which appeared in 1976. Motorola simultaneously launched the 68HC05, and Zilog introduced the Z80 series. These early microcontrollers all contained 256 bytes of RAM, 4K of ROM, 4 8-bit parallel ports, 1 full-duplex serial port, and two 16-bit timers. Subsequently, in the early 1980s, Intel further improved the 8048 and successfully developed the 8051, marking a significant milestone in the history of microcontrollers. To this day, the 51 series microcontrollers remain the most successful microcontroller chips, widely used in various products.
The emergence of embedded systems was initially based on microcontrollers. From the appearance of microcontrollers in the 1970s to the large-scale application of various embedded microprocessors and microcontrollers today, devices such as automobiles, home appliances, industrial machines, communication devices, and thousands of other products can achieve better performance through embedded electronic devices: easier to use, faster, and cheaper. These devices initially exhibited characteristics of embedded applications, but at that time, they only used 8-bit chips to execute some single-threaded programs, and the concept of a “system” was not yet discussed.
Starting in the early 1980s, embedded system programmers began to use commercial-grade “operating systems” to write embedded application software, which allowed for shorter development cycles, lower development costs, and higher development efficiency, leading to the true emergence of “embedded systems.” More precisely, the operating systems at this time were real-time kernels, which included many features of traditional operating systems, such as task management, inter-task communication, synchronization and mutual exclusion, interrupt support, and memory management.
Notable examples include VRTX from Ready System, PSOS from Integrated System Incorporation (ISI), VxWorks from IMG, and QNX from QNX Company. These embedded operating systems all possess typical characteristics of embedded systems: they adopt preemptive scheduling, have very short response times, and the execution time of tasks can be determined; the system kernel is small, with features of being customizable, extensible, and portable, allowing it to be ported to various processors; they exhibit strong real-time performance and reliability, making them suitable for embedded applications. The emergence of these embedded real-time multitasking operating systems has liberated application developers from small-scale development and has also promoted a broader application space for embedded systems.
After the 1990s, with increasing demands for real-time performance and the growing scale of software, real-time kernels gradually evolved into real-time multitasking operating systems (RTOS), which have become the mainstream software platform for international embedded systems. At this time, more companies recognized the vast development prospects of embedded systems and began to vigorously develop their own embedded operating systems. In addition to the aforementioned established companies, new embedded operating systems such as Palm OS, Win CE, embedded Linux, Lynx, Nucleux, and domestic systems like Hopen and Delta OS have emerged. With the increasingly broad development prospects of embedded technology, it is believed that more embedded operating system software will appear.
Several Embedded Real-Time Operating Systems Suitable for the PIC18F Series Microcontrollers
As shown in the figure below:
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Embedded systems are user-oriented, product-oriented, and application-oriented; they must be combined with specific applications to have vitality and advantages. Therefore, the meanings of the above three orientations can be understood as follows: embedded systems are closely integrated with applications, possessing strong specificity, and must be reasonably tailored to meet actual system requirements.
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Embedded systems are the product of combining advanced computer technology, semiconductor technology, and electronic technology with specific applications in various industries. This determines that they are a technology-intensive, capital-intensive, highly decentralized, and continuously innovative knowledge integration system. Therefore, entering the embedded system industry requires a correct positioning. For example, Palm occupies over 70% of the PDA market because it focuses on personal electronic consumer goods, emphasizing graphical interfaces and multitasking management; while Wind River’s VxWorks is used in Mars rovers due to its high real-time performance and reliability.
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Embedded systems must tailor hardware and software according to application requirements to meet the functional, reliability, cost, and size requirements of the application system. Therefore, establishing a relatively generic hardware and software foundation and then developing systems that adapt to various needs is a better development model. Currently, the core of embedded systems is often a microkernel of only a few kilobytes to several tens of kilobytes, which needs to be functionally expanded or tailored based on actual usage. However, due to the existence of the microkernel, such expansions can be carried out very smoothly.
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