Comprehensive Comparison of Common Embedded Processors

EmbeddedProcessor Overview

Embedded processors are the core of embedded systems, serving as the hardware unit that controls and assists system operation. The range is extremely broad, from the initial 4-bit processors, the still widely used 8-bit microcontrollers, to the latest 32-bit and 64-bit embedded CPUs that are widely favored.

Since the advent of microprocessors, embedded systems have developed rapidly, and embedded processors are undoubtedly the core part of embedded systems, directly affecting the performance of the entire embedded system. Typically, embedded processors are regarded as the general term for the core computing and control devices in embedded systems.

There are over 1000 types of processors in the world with embedded functionality, with popular architectures including more than 30 series such as MCU and MPU. Given the vast development prospects of embedded systems, many semiconductor manufacturers are producing embedded processors on a large scale, and companies designing their own processors have also become a major trend in the future embedded field, with various types from microcontrollers, DSPs to FPGAs, becoming faster, more powerful, and cheaper. The addressing space of embedded processors can range from 64kB to 16MB, with processing speeds reaching up to 2000 MIPS, and packages ranging from 8 pins to 144 pins.

Comprehensive Comparison of Common Embedded Processors

Features

Embedded microprocessor design is similar in basic principles to that of ordinary desktop computer microprocessors, but with higher stability, lower power consumption, strong adaptability to environments (such as temperature, humidity, electromagnetic fields, vibrations, etc.), smaller size, and more integrated functions. In the desktop computer field, the main indicator for comparing processors is computing speed, from the 33MHz clock frequency of the 386 computer to the 3GHz clock frequency of the Pentium 4 processor, with speed being the primary concern for users. However, in the embedded field, the situation is completely different. The choice of embedded processors must be made according to design requirements, balancing many factors such as performance, power consumption, functionality, size, packaging form, SoC level, cost, and commercial considerations.

As the core of embedded systems, embedded processors are responsible for important tasks of control and system operation, enabling host devices to have intelligent functions, flexible design, and ease of operation. Generally speaking, embedded processors have the following characteristics: strong real-time multitasking support capability, memory protection features, expandable microprocessor architecture, strong interrupt processing capability, and low power consumption.

The core of embedded systems is the embedded microprocessor. Embedded microprocessors generally have the following four characteristics:

1) Strong support for real-time multitasking, capable of completing multiple tasks with a short interrupt response time, thereby minimizing the execution time of internal code and real-time core.
2) Strong memory protection features.This is because the software structure of embedded systems is modularized, and to avoid erroneous cross-interactions between software modules, powerful memory protection features need to be designed, which also facilitates software diagnostics.
3) Expandable processor architecture to quickly develop the highest performance embedded microprocessors that meet applications.
4) Embedded microprocessors must have very low power consumption, especially in portable wireless and mobile computing and communication devices powered by batteries, where power consumption needs to be at the mW or even μW level.

Classification

1. Microprocessor

Embedded microprocessors (Micro Processor Unit, MPU) have evolved from the CPUs of general-purpose computers. They are characterized by having processors with more than 32 bits, offering high performance, though at a correspondingly higher price. However, unlike computer processors, in actual embedded applications, only the hardware functions closely related to embedded applications are retained, while other redundant functional parts are removed, achieving the special requirements of embedded applications with the lowest power consumption and resources. Compared to industrial control computers, embedded microprocessors have advantages of small size, light weight, low cost, and high reliability. Main types of embedded processors include Am186/88, 386EX, SC-400, Power PC, 68000, MIPS, and ARM/StrongARM series.

Among them, ARM/StrongARM is an embedded microprocessor developed specifically for handheld devices, falling into the mid-range price category.

2. Microcontroller

The typical representative of embedded microcontrollers (Microcontroller Unit, MCU) is the microcontroller, which has been in wide application in embedded devices since its emergence in the late 1970s, despite having over 20 years of history. Microcontroller chips integrate various necessary functions and peripherals, including ROM/EPROM, RAM, buses, bus logic, timers/counters, watchdogs, I/O, serial ports, PWM outputs, A/D, D/A, Flash RAM, EEPROM, etc. Compared to embedded microprocessors, microcontrollers are characterized by their single-chip design, greatly reducing size, which in turn lowers power consumption and cost, while enhancing reliability. Microcontrollers are the mainstream in industrial embedded systems. The on-chip peripheral resources of microcontrollers are generally rich, making them suitable for control, hence the name microcontroller.

Due to the low price and excellent functionality of MCUs, they have the most varieties and numbers, with representative models including 8051, MCS-251, MCS-96/196/296, P51XA, C166/167, 68K series, and MCU 8XC930/931, C540, C541, as well as many specialized MCUs supporting I2C, CAN-Bus, LCD, and numerous compatible series. MCUs account for about 70% of the embedded system market share. Atmel’s AVR microcontroller, which integrates devices like FPGAs, has a high cost-performance ratio and is expected to drive further development of microcontrollers.

3. DSP Processor

Embedded DSP processors (Embedded Digital Signal Processor, EDSP) are specifically designed for signal processing, with special designs in system architecture and instruction algorithms that provide high compilation efficiency and instruction execution speed. DSPs are widely used in various instruments for digital filtering, FFT, spectral analysis, etc.

The theoretical algorithms for DSP emerged in the 1970s, but due to the absence of dedicated DSP processors, these theoretical algorithms could only be implemented through MPUs and other discrete components. The lower processing speed of MPUs could not meet the algorithm requirements of DSPs, limiting their application to some cutting-edge high-tech fields. With the development of large-scale integrated circuit technology, the world’s first DSP chip was born in 1982, operating several times faster than MPUs and widely used in voice synthesis and codec applications. By the mid-1980s, with advances in CMOS technology, the second generation of DSP chips based on CMOS technology emerged, significantly increasing both storage capacity and processing speed, laying the foundation for voice processing and image hardware processing technologies. By the late 1980s, the processing speed of DSPs further improved, and their application fields expanded from the aforementioned areas to communications and computing. After the 1990s, DSPs evolved into fifth-generation products, with even higher integration and broader application scopes.

The most widely used are TI’s TMS320C2000/C5000 series, along with Intel’s MCS-296 and Siemens’ TriCore, each having their respective application areas.

4. System on Chip

Embedded Systems on Chip (SoC): SoC aims to achieve the maximum integration of product systems and is one of the hot topics in the embedded application field. The biggest feature of SoC is the successful realization of seamless integration of hardware and software, directly embedding the operating system code modules within the processor chip. Moreover, SoC has extremely high comprehensiveness, using hardware description languages like VHDL to implement complex systems on a single silicon chip. Users no longer need to draw large and complex circuit boards like traditional system designs, connecting and soldering them bit by bit; they can directly call various standard general-purpose processors from the device library using precise languages, and after simulation, they can be directly delivered to chip manufacturers for production. Since the majority of system components are within the system, the entire system is particularly simple, not only reducing the size and power consumption of the system but also improving reliability and design production efficiency.

Since SoCs are often specialized, most are not known to users. A typical SoC product is Philips’ Smart XA. A few general-purpose series include Siemens’ TriCore, Motorola’s M-Core, and certain ARM series devices, as well as the Neuron chip developed jointly by Echelon and Motorola.

It is expected that in the near future, some major chip companies will launch mature SoC chips that can capture a majority of the market, defeating competitors in one fell swoop. SoC chips will also play an important role in applications such as sound, image, film, network, and system logic.

Summary of Embedded Processors (Common)

(1) Embedded ARM Microprocessors (Embedded Microprocessor Architecture)

The Origin and Development of ARM Microprocessors

ARM (Advanced RISC Machines) can be considered a company name, a general term for a class of microprocessors, or a name for a technology. Currently, microprocessors using ARM technology intellectual property (IP) cores are what we commonly refer to as ARM microprocessors. They are high-performance, low-power 32-bit microprocessors widely used in embedded systems. Microprocessors based on ARM technology occupy over 75% of the market share for 32-bit RISC microprocessors, and ARM technology is gradually infiltrating all aspects of our lives. ARM9 represents the mainstream processors of ARM and has been widely applied in handheld phones, set-top boxes, digital cameras, GPS, personal digital assistants, and Internet devices.

Application Areas of ARM Microprocessors

ARM microprocessors are currently very widely used across various application areas. To date, applications of ARM microprocessors and technology have almost penetrated various product markets including industrial control, consumer electronics, communication systems, network systems, and wireless systems.
1. Industrial Control: As a 32-bit RISC architecture, microcontroller chips based on ARM cores not only occupy a large share of the high-end microcontroller market but are also gradually expanding into low-end microcontroller application areas. The low power consumption and high cost-performance ratio of ARM microcontrollers challenge traditional 8-bit/16-bit microcontrollers.
2. Wireless Communication: Currently, over 85% of wireless communication devices use ARM technology, with ARM solidifying its position in this field due to its high performance and low cost.
3. Network Applications: With the promotion of broadband technology, ADSL chips using ARM technology are gradually gaining competitive advantages. Additionally, ARM has optimized voice and video processing and gained widespread support, challenging the application fields of DSPs.
4. Consumer Electronics: ARM technology is widely used in popular digital audio players, digital set-top boxes, and gaming consoles.
5. Imaging and Security Products: The vast majority of popular digital cameras and printers use ARM technology. The 32-bit SIM smart cards in mobile phones also use ARM technology.

Characteristics of ARM Microprocessors Based on RISC Architecture

1. Small size, low power consumption, low cost, high performance;
2. Supports Thumb (16-bit)/ARM (32-bit) dual instruction sets, well compatible with 8-bit/16-bit devices;
3. Extensive use of registers, faster instruction execution speeds;
4. Most data operations are completed within registers;
5. Flexible and simple addressing modes, high execution efficiency;
6. Fixed instruction length;

(2) Embedded MIPS Processors

Overview of MIPS Processor Development

MIPS is a very popular type of RISC processor worldwide. MIPS stands for “Microprocessor withouT Interlocked piped stages,” and its mechanism aims to avoid data-related issues in the pipeline as much as possible through software methods. MIPS Technologies is a well-known chip design company in the United States that designs chips using a Reduced Instruction Set Computing (RISC) architecture, manufacturing high-performance, high-end, and embedded 32-bit and 64-bit processors, holding an important position in the RISC processor field.

MIPS has an advanced system architecture and design philosophy, with its instruction system having matured from the general-purpose processor instruction systems MIPSI, MIPSII, MIPSIII, MIPSIV to MIPSV, and the embedded instruction systems MIPS16, MIPS32 to MIPS64.

In terms of design philosophy, MIPS emphasizes the collaboration between hardware and software to improve performance while simplifying hardware design. Compared to the complex instruction set computing (CISC) architecture used by Intel, RISC has advantages such as simpler design, shorter design cycles, and the ability to apply more advanced technologies to develop faster next-generation processors.

MIPS is one of the earliest commercial RISC architecture chips, and the new architecture integrates all original MIPS instruction sets while adding many more powerful features.

Applications of MIPS Processors

In general, MIPS R series microprocessors are used to build SGI’s high-performance workstations, servers, and supercomputing systems. In the embedded field, MIPS K series microprocessors are currently one of the most widely used processors after ARM (before 1999, MIPS was the most used processor in the world), with applications covering game consoles, routers, laser printers, handheld computers, and more.

(3) PowerPC

The PowerPC architecture specification was developed in the 1990s by IBM, Apple, and Motorola, resulting in multi-processor computers based on PowerPC.

The PowerPC architecture is characterized by good scalability and convenience. It is a 64-bit specification (also includes a 32-bit subset). Almost all commonly available PowerPCs (except for the new IBM RS/6000 and all IBM pSeries high-end servers) are 32-bit.

PowerPC’s market share is not very high, but it is widely used in the control and management of communication systems.

(4) Embedded x86 Processors

x86 is an abbreviation for the standard numbering of Intel’s general-purpose computer series, also denoting a set of general computer instruction sets. The ‘X’ has no relation to the processors; it is a simple wildcard definition for all *86 systems, such as: i386, 586, Pentium. Since early Intel CPUs were numbered like 8086, 80286, and since all CPUs in this series are instruction-compatible, they are all designated as x86, meaning they use the x86 instruction set. Today’s Pentium, P2, P4, and Celeron series all support the x86 instruction system, thus belonging to the x86 family.

x86 has become the standard computing platform due to its unparalleled performance-to-price ratio. However, x86 is still based on 32-bit technology—incapable of handling high-end enterprise-level servers and workstation applications. Compared to ARM architecture products, embedded x86 processors generally have much higher performance, but also higher power consumption. Although they can still maintain fanless operation, they cannot be used in PDA, smartphones, and other handheld computing products that rely entirely on battery operation. The real demand for embedded x86 processors arises in areas such as network terminals, thin clients, low-cost/low-power PCs, and home consumer electronics that require continuity in PC software. The corresponding devices are relatively larger, not battery-powered, but require high performance, low power consumption, low noise, and high reliability. In 2006, x86 launched its first dual-core processor.

Compared to ARM and MIPS, the application range of embedded x86 processors is narrower. They are mainly used in desktop and low-end server processors.

(5) Embedded DSP Processors

DSPs are dedicated processors for high-speed real-time processing after converting analog signals into digital signals, with processing speeds 10 to 50 times faster than the fastest CPUs. In today’s digital age, DSPs have become fundamental devices in communication, computing, and consumer electronics. Industry insiders predict that DSPs will be the fastest-growing electronic products in future integrated circuits and will be the decisive factor in the update of electronic products.

DSPs belong to the Modified Harvard architecture, meaning they have two internal buses: a data bus and a program bus. The program and data storage spaces are separate, each with independent address and data buses, allowing addressing and reading to occur simultaneously. Currently, they have achieved floating-point operations of 9 billion times per second (9000 MFLOPS). They utilize pipelining, where the execution of each instruction is divided into several steps: fetching the instruction, decoding, fetching data, and executing, allowing multiple functional units within the chip to complete these steps, effectively executing multiple instructions in parallel and significantly increasing processing speed. Multiplication instructions are completed in a single cycle, optimizing algorithms for convolution, digital filtering, FFT, correlation, matrix operations, etc. Special instructions such as circular addressing and bit-reversed addressing greatly enhance the addressing, sorting, and computation speed in operations like FFT and convolution, with the time for 1024-point FFT now less than 1μs. They feature independent DMA buses and controllers, with one or more independent DMA buses working in parallel with the CPU’s program and data buses, achieving speeds over 800 Mbytes/s without affecting CPU operations. Multi-processor interfaces allow multiple processors to work together easily, either in parallel or serially, to enhance processing speed.

DSP processors have evolved into embedded DSP processors (Embedded Digital Signal Processor, EDSP) through integration, EMC modifications, and the addition of on-chip peripherals, or by adding DSP coprocessors to general microcontrollers or SoCs. The main driving factor behind the development of embedded DSP processors is the intelligence of embedded systems. Currently, semiconductor manufacturers such as TI, ADI, Freescale, and CEVA have strong capabilities in this field.

The main market for general DSPs lies in communication applications, while embedded DSPs are primarily used in consumer electronics such as DVD players and recorders, set-top boxes, audio and video receiving devices, MP3 players, and digital cameras. However, communication chips for WLAN, DSL, and cable broadband networks also incorporate embedded DSPs.

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