Classification and Composition of Embedded Systems

(1) Embedded Microprocessor Unit (EMPU)

• The foundation of an embedded microprocessor is the CPU from a general-purpose computer. In applications, the microprocessor is mounted on a specially designed circuit board, retaining only the motherboard functions relevant to the embedded application, which significantly reduces the system's size and power consumption. To meet the special requirements of embedded applications, while the functions of embedded microprocessors are essentially the same as standard microprocessors, they are generally enhanced in terms of operating temperature, electromagnetic interference resistance, and reliability.
• Compared to industrial control computers, embedded microprocessors have the advantages of small size, light weight, low cost, and high reliability. However, the circuit board must include ROM, RAM, bus interfaces, and various peripherals, which reduces the system's reliability and technical confidentiality.
• Current embedded processors mainly include ARM from ADVANCED RISC MACHINES, MIPS from SILICON GRAPHICS, POWER PC from IBM and MOTOROLA, X86 and I960 chips from INTEL, AM386EM from AMD, and SH RISC chips from HITACHI.

(2) Microcontroller Unit (MCU)

• Embedded microcontrollers are also known as single-chip microcomputers. An embedded microcontroller generally centers around a microprocessor core, with integrated ROM, EPROM, RAM, Flash RAM, bus, bus logic, timers/counters, WatchDog, serial ports, pulse width modulation output, A/D converters, and other necessary functions and peripherals. Compared to embedded microprocessors, the most significant feature of microcontrollers is their single-chip design, which greatly reduces size, thereby lowering power consumption and cost, and increasing reliability.
• Microcontrollers are currently the mainstream in the embedded systems industry, accounting for 70% of the entire embedded market. The on-chip peripheral resources of microcontrollers are generally quite rich, making them suitable for control applications, hence the name microcontroller.
• General series: 8051, P51XA, MCS-251, MCS-96/196/296, C166/167, MC68HC05/11/12/16, 68300, etc.
• Semi-general series: MCUs supporting USB interfaces like 8XC930/931, C540, C541;
• Specialized series: MCUs supporting I2C, CAN-Bus, LCD, and compatible series.
• Many microprocessors are gradually evolving into microcontrollers (MCUs), such as ARM, leading to a convergence of these concepts.

(3) Embedded Digital Signal Processor (EDSP)

• DSP processors have specially designed system architectures and instructions, making them suitable for executing DSP algorithms, with high compilation efficiency and instruction execution speed. In areas like digital filtering, FFT, and spectral analysis, DSP algorithms are increasingly entering the embedded domain, transitioning from implementing DSP functions with general instructions in universal microcontrollers to using embedded DSP processors.
• Two developmental sources of embedded DSP processors:
① DSP processors become embedded DSP processors through single-chip design, EMC modifications, and adding on-chip peripherals, such as TI's TMS320C2000/C5000 series;
② Adding DSP coprocessors to universal microcontrollers or System On Chip (SOC), such as Intel's MCS-296 and Infineon(Siemens)'s TriCore.
• The intelligence of embedded systems is another factor driving the development of embedded DSP processors, such as various consumer products with intelligent logic, biometric terminals, keyboards with encryption algorithms, ADSL access, real-time voice compression systems, and virtual reality displays. These intelligent algorithms generally require significant computational power, especially in vector operations and pointer linear addressing, which are strengths of DSP processors.
• Representative embedded DSP processors include TI's TMS320 series and Motorola's DSP56000 series.

(4) System On Chip (SOC)

• SOC is a new form of embedded systems, integrating microprocessors, analog IP cores, digital IP cores, and memory (or off-chip memory control interfaces) on a single chip. It is usually custom-made or a standard product for specific uses, implementing the hardware integrated circuits and embedded software needed to perform a computer system's functions on a single silicon chip, representing a new interdisciplinary field between computer science and microelectronics.
• The design basis of SoC is IP (Intellectual Property) reuse technology.
• An IP module is a pre-designed, verified integrated circuit, device, or component with a certain function.
• Two different forms: soft IP cores and hard IP cores
• Advantages of SOC:
• Reduced power consumption
• Smaller size
• Enhanced system functionality
• Increased speed
• Cost savings

II. Composition of Embedded Systems

Embedded systems consist of hardware and software, used to control, monitor, or manage other devices. The former is the physical foundation of the entire system, providing a platform for software operation and communication interfaces; the latter actually controls the system's operation.
Hardware: Embedded microprocessor, peripheral circuits, peripheral hardware devices.
Software: BOOTLOADER, embedded operating system, user applications, etc.

(1) Hardware

Hardware: Embedded microprocessor, peripheral circuits, peripheral hardware devices.
➢ The CPU is the core processor of the embedded system, also known as the embedded microprocessor, responsible for controlling the execution of the entire embedded system;
➢ Peripheral circuits include the system's memory, I/O ports, reset circuits, ADC/DAC (analog-to-digital converter/digital-to-analog converter), and power supply, forming a complete embedded target system with the core processor.
➢ SRAM (Static Random Access Memory) is static random access memory
➢ FLASH is flash memory, a type of solid-state storage
➢ DRAM (Dynamic Random Access Memory) is dynamic random access memory
➢ External devices refer to various devices that interact with the real environment, including USB (Universal Serial Bus), storage devices, mouse, keyboard, LCD (Liquid Crystal Display), infrared data transmission (IRDA, Infrared Data Association), and printing devices.

(2) Software

• Software: BOOTLOADER, embedded operating system, user applications.
➢ BOOTLOADER completes the initial hardware environment setup, preparing a working environment for the firmware library or operating system.
➢ The operating system controls the interaction between applications and hardware, performing real-time and multitasking operations; or user programs interact with hardware through the firmware library.
➢ Applications control the system's operation and behavior, fulfilling various design functions.
The software of embedded systems can be divided into 4 layers:
① Device Driver Interface (DDI) is responsible for the information interaction between the embedded system and external devices;
② Real-Time Operating System (RTOS) is divided into basic and extended parts,
➢ The basic functions are the core of the operating system, responsible for task scheduling, memory allocation, clock management, and interrupt management, providing basic services like file and graphical user interface (GUI);
➢ The extended functions provide users with extended functionalities of the operating system, including network and database;
③ Programmable Application Interface (API), also known as programming middleware or application middleware, provides various programming interface libraries for application development, tailored to different application fields and security requirements, thereby reducing the burden on application developers;
④ Application software is the software written by developers for different applications.