Catalog
Brief Introduction of SoC
A system on chip (SoC) is a microchip which has all the necessary electronic circuits and other parts of a given system on a single integrated circuit. This technology is especially used in small yet extremely complex consumer electronic devices. There are some devices which have more processing power and memory than a standard desktop. This is possible only with the use of system on chip design.
In simple terms a system on chip is an integrated circuit which integrates all components of a computer or any other electronic system into a single chip. It may include analog, digital, mixed-signal and other radio frequency funtions on a single chip substrate. Due to their low power consumption, SoCs are quite common in the mobile electronics market. Embedded systems is the best example of the use of system on chip.
Figure 1
The structure of a typical system of chip consists of:
—A microcontroller, digital signal processor or microprocessor core.
—Memory blocks along with a selection of RAM, ROM, EEPROM and flash memory.
—Oscillators, phase-locked loops and other timing sources.
—Counter-timers, eral-time timers as well as power-on reset generators.
—USB, FireWire, Ethernet, SPI, USART and other external interfaces as well.
—Analog interfaces including ADCs and DACs.
Along with the above mentioned hardware, system on chip design also has software which controls the microcontroller, microprocessor, peripherals and interfaces. The design flow of a SoC aims at developing both the hardware and software in a parallel manner. Typically most of the system on chip are developed from pre-qualified hardware blocks along with the software drivers which control their operation. While the hardware blocks are arranged together with the help of CAD tools, software-development environment is used to integrate the software modules.
The next step is functional verification of the system on chip design to verify and debug both harware as well as software prior to tapeout. The technologies with which SoC can be fabricated are:
—Standard Cell
—Full Custom
—Field-programmable Gate Array
As SoC designs consume less power and have higher reliability and lower cost as compared to the multi-chip systems which they replace, they are regarded as the best option to be used.
The major problems/ challenges faced by SoC designers are as follows:
Functional content complexity – The amount of the content involved in build SoCs leads one to the conclusion that designing these systems is not easy even for large design teams. This is why some form of intellectual property reuse has become an inevitable part of SoC design.
Along with functional content complexity, architectural as well as verification challenge are some of the major problems inherent in the SoC designing.
Content of The Study
SoC design methodology mainly studies Bus Architecture Technology, IP Core Reuse Technology, Reliability Design Technology, Software and Hardware Co-design Technology, SoC Design Verification Technology, Chip Synthesis / Timing Analysis Technology, Testability / Debuggability Design Technology, Low Power Consumption Design Technology, New Circuit Implementation Technology, etc. In addition, Operating System / Embedded Software Migration, Development and Research are also needed to be done in this new interdisciplinary field of research.
Bus Architecture Technology
Bus structure and interconnection technology directly affect the overall performance of the chip. For a single application field, mature bus architecture can be selected; for those with high serialization or comprehensive performance requirements, in-depth architecture research can be carried out, and the bus architecture with its own characteristics can be constructed. Therefore, it can be refined and strengthened without being restricted by third parties, develop synchronously with the system and become more competitive. At present, the development of SoC is mainly based on platform (including independent construction of the overall architecture), based on core, based on synthesis and other methods, and constantly introduce better performance, stronger scalability of the bus specification.
IP Core Reuse Technology
IP core is generally divided into hard IP core, soft IP core and firm IP core. Hard IP core refers to the IP core which has been pre-arranged and cannot be modified by the system designer. The soft IP core is usually submitted in the form of HDL language. Firm IP core is composed of RTL description and synthesizable network table. The research focus of IP core reuse is to develop the integration of specification and testability to adapt to a variety of bus interfaces in order to achieve the purpose of reuse with as few outsourcing and test vectors as possible. IP cores should have good development documentation and reference manuals, including data manuals, user guidelines, simulation and reuse models, and compatibility is an important factor.
Reliability Design Technology
Because SoC is composed of multi-level bus and each bus contains multiple devices (IP core). Therefore, it is very important to ensure the normal operation of the whole chip. And the anti-"deadlock" mechanism and "unlocking" mechanism must be considered, which means that a device (IP core) will not affect the other functions of the whole chip even if it is paralyzed. In addition, with the development of ultra-deep submicron technology, the reliability of bus transmission becomes a serious challenge, so it is necessary to study the fault-tolerant mechanism and fault recovery mechanism.
Software and Hardware Co-design Technology
Due to the pressure of market and design risk, SoC hardware and software co-design becomes particularly important. Improving hardware / software co-description, co-analysis, co-design, co-simulation and co-verification can greatly reduce the risk of hardware design and shorten the development and debugging time of embedded software. At the same time, the fatal problems existing in the software and hardware can be found in the co-verification environment in time, and the readjustment of the software and hardware can be avoided in the final integration test.
SoC Design Verification Technology
It is mainly divided into three levels: IP core verification, IP core and bus interface compatibility verification and system-level verification, including design concept verification, design implementation verification, design performance verification, fault simulation, chip testing and so on. From the type of verification, there are compatibility test, corner test, random test, real code test, regression (Regression) test, assertion verification and so on. Due to the increasing complexity of the chip and the high cost of software simulation, hardware simulation verification has become an important verification method. Verification accounts for about 70% of the whole design work. And how to improve the verification coverage and efficiency is the eternal topic of design verification.
Chip Synthesis / Timing Analysis Technology
Due to the increasing complexity and scale of SoC system, new topics such as multi-clock, multi-voltage and ultra-deep submicron continue to emerge, which puts forward higher requirements for the comprehensive research of SoC. In particular, the research on how to classify and decompose the time series budget and special constraints of critical path requires researchers to master a great deal of system background knowledge. At the same time, the static timing analysis (STA) is becoming more and more complex and the efficiency of back-end dynamic simulation is low, which poses a severe challenge to the overall designers.
Testability / Debuggability Design Technology
This paper mainly studies and solves the problems of batch production testability and online debuggability. The implementation technologies include DFT, SCAN, BIST, Iddq, JTAG/eJTAG. To study the SoC test architecture based on various IP cores and test the efficient transitivity of vector, It is more important to consider the parallelization of testing and reduce the time occupied by chip testing. In addition, we should pay attention to online debugging to facilitate users to develop and debug SoC-based products.
Low Power Consumption Design Technology
Low power consumption has become an equally important design goal as area and performance, so accurate evaluation of power consumption has also become an important issue. The power consumption of the chip is mainly composed of jump power consumption, short circuit power consumption and leakage power consumption. In order to reduce power consumption, it is necessary to study the circuit implementation technology, input vector control (IVC) technology, multi-voltage technology, power consumption management technology and software (algorithm) low-power utilization technology from the perspective of SoC multi-level stereo to solve the problem comprehensively.
New Circuit Implementation Technology
Due to the sharp increase in the number of transistors, the decreasing chip size, the increasing density, the increased reuse frequency of IP cores, the emergence of low voltage, multi-clock, high frequency, high testability, new and difficult packaging and other requirements, as well as the endless emergence of new design technologies, the minimum dimensions of semiconductor technologies develop towards deep submicron. And this requires SoC designers to constantly study new technologies, new tools, key circuit architecture, timing convergence, signal integrity, antenna effect and so on.
Embedded Software Migration / Development
The main research and development of BIOS and embedded operating system transplantation / development of SoC is to support multi-task, to make program development easier, to improve the stability and reliability of the system, to make maintenance convenient, to make reading and understanding easier. Therefore, it should have the characteristics of good security, strong robustness, high code execution efficiency and so on. For example, the embedded Linux operating system code implantation research on SoC chip can reduce the difficulty based on BSP development for system developers. At the same time, it improves the development efficiency and shortens the development cycle.
SoC classification
In this paper, SoC is classified into three categories: CSoC, SOPC and ASIC SoC, and then unified them into SoC architecture classification model.
Technical characteristics of CSoC
CSoC is generally composed of processor, memory, ASIC-based kernel and on-chip reconfigurable components, which has obvious advantages over ASIC SoC and multi-chip board-level development based on standard components. It is characterized by:
—CPU + reconfigurable processing artifacts.
—Efficiency and flexibility combine well.
—Refactoring based determination processing function.
—It is superior to supercomputer in image processing, pattern matching and so on.
—According to the needs of the task, it can be dynamically reconfigurable to improve the performance-price ratio.
At present, the academia pays more attention to the XPP (eXtreme Processing Platform), which is the efficient processor with dynamic reconfiguration. XPP embeds programmable logic modules in a SoC based on a microprocessor core based on a bus architecture to form a reconfigurable SoC platform, as shown in figure 1. The applicable reconfigurable data processing architecture is often composed of processing array element (PAE), communication network packet oriented, hierarchical reconfiguration management tree (CM) and I/O module. XPP has the ability to automatically reconstruct streams and process data streams, breaking through the traditional John von Neumann instruction stream mode. Because of the high degree of regularity, it is easy to obtain instruction-level parallelism and pipeline efficiency.
Figure 2. CSoC Architecture based on XPP/Leon
Technical characteristics of SoPC
SoPC is a special on-chip system. It is a programmable system which has flexible design mode. It can be cut, expanded and upgraded and it also has programmable functions in the development of software and hardware on-line system. It combines the advantages of SoC and FPGA, including the following basic characteristics:
—Contains at least one embedded processor IP core
—Small capacity on-chip high-speed RAM resources
—Rich IP core resources for choice
—Sufficient on-chip programmable logic resources
—Shared or coexisting processor debugging interface and FPGA programming interface
—May contain partially programmable analog circuits
The block diagram of SoPC is shown in figure 2. In addition to the above characteristics, it also involves the software and hardware co-design technology, which has aroused widespread concern at present. Because the main logic design of SoPC is carried out in programmable logic devices, and BGA packaging has been widely used in the field of micropackaging, traditional debugging equipment, such as logic analyzer and digital oscilloscope, has been difficult to carry out direct test and analysis. Therefore, it is necessary to put forward higher requirements for software and hardware co-design technology based on simulation technology. At the same time, new debugging technology has been emerging.
Figure 3. The block diagram of SoPC
Technical characteristics of ASIC SoC
ASIC SoC is an application-specific on-chip system, which has the characteristics of high performance, strong real-time, high reliability, low power consumption, low cost and so on. It generally has the following basic characteristics:
—At least one CPU kernel.
—Normative bus architecture
—RAM resources (or on-chip memory access controller)
—An appropriate amount of I/O equipment (including analog ones)
—Extensible interfaces (such as PCI)
—On-line debugging port (eJTAG)
—Circuits with testability
Figure 4. L*BUS Bus Architecture Diagram
ASIC SoC is generally a product based on IP core or SoC development platform. It requires expertise, IP libraries, SoC bus architecture, and embedded software support (including BIOS, OS). It also requires a wide range of multifunctional IP cores and the design to integrate customer logic with it to meet customers’ needs for product development. SoC designers not only take advantage of the latest technology, but also reduce the development cycle and risk by reusing the proven IP core.
At present, there are many kinds of SoC bus architecture and each of them is developed to meet the requirements of its specific application field. Some are suitable for downmarket embedded products, some are suitable for handheld products, and some are suitable for high-energy products. In a word, everyone has its own advantages. The development of SoC cannot be separated from the constraints of power consumption, performance, cost, testability, reliability, IP core reusability, platform technical support and software and hardware’s co-development. Developers need to have a strong background in computer architecture in order to support its rapid development.
Classification principles of SoC
SOC can be classified according to the architecture it adopts:
One is the architecture based on instruction stream computing, which is typically represented by the traditional ASIC SoC. According to the control of instruction stream and data stream, this type can be divided into SISD (single instruction stream-single data stream), SIMD (single instruction stream-multiple data stream), MISD (multiple instruction stream-single data stream) and MIMD (multiple instruction stream-multiple data stream) in order to flexibly adapt to the needs of different algorithms in various applications.
The second one is an architecture based on data stream computing, which only controls the input / output data of the unit. Working according to the principle of data stream, it is more efficient than instruction stream, but less flexible. Pulsating array based on data stream computing is a typical architecture of this kind. A pulsating array is an array of data path components DPU (Data Path Unit). The data streams out of the data memory according to the beat, completes the calculation through the PU array, and the result flows back to the data memory. PU arrays have only the ability to control data, which is also the origin of FlowWare. Conventional SoPC is its typical technical representative.
The third is the architecture based on configuration stream computing. Using coarse-grained FPGA chip as carrier，SoC can dynamically reconstruct the hardware form of architecture design by adopting Morphwave. It can be an array of rPU (reconfigurable Processing Unit) and implemented by Configuwave. The configuration stream comes from the configuration memory called CM (reConfiguration Memory), which controls the changes of the rPU array through reConfiguration Manager and works according to the principle of data stream. CSoC is its typical technical representative.
Classification model of SoC
According to the classification principles of the SoC architecture mentioned above, we establish a three-dimensional classification model of CDI architecture on the basis of the concepts of instruction stream, data stream and configuration stream, corresponding to I (Instruction Stream Architecture) axis, D (Data Stream Architecture) axis and C (reConfiguration Stream Architecture) axis. And it is shown in figure 4.
Any SoC with hybrid computer architecture of instruction stream computing, data stream computing and configuration stream computing can be summarized in CDI three-dimensional space. There are four basic architecture classifications on I axis: SISD, SIMD, MISD and MIMD. On the D axis, there are only two basic states: single data stream architecture and multiple data stream architecture. And there are also only two basic states on the C axis: single reconfiguration stream architecture and multiple reconfiguration stream architecture.
Figure 5. CDI Classification Model Diagram
Development Direction of SoC Technology
Since the concept of SoC was put forward in the late 1990s, the technology has been developed rapidly. Whether it is CSoC, SoPC or ASIC SoC, all of them are gradually related to computer science, microelectronics, materials and technology, electronic communication and so on. Their interdisciplinary development provides a strong support for the technical development of SoC.
Computer Science promotes the level of SoC Technology
John von Neumann architecture and data stream architecture are the mainstream architectures of computers. The first one is characterized by the integration of program and data while the second one is characterized by the separation of program and data. The miniaturization of general purpose computer provides a source for the development of SoC technology.
Bus Architecture Technology, Algorithm Implementation Technology, Modular Design Technology, BIOS Technology, Software Engineering Technology, Software and Hardware Debugging Technology, System Verification Technology, performance Evaluation Technology, Real-time Processing Technology, Reliability Design Technology, Human-computer Interaction Technology, Load Balancing Technology and Low-power Consumption Design Technology in computer field are all reflected in SoC design technology. It also promotes the rapid development of SoC in a few years and becomes one of the main development directions of computers in the post-PC era.
Although the development of SoC technology is closely related to the development of technology and the improvement of EDA design means, its core is CPU core, bus architecture and various IP cores. In the overall performance evaluation and implementation technology, all of them are related to the computer professional field. Especially in upmarket applications, such as multi-CPU core integration and heterogeneous integration and other system requirements, computer science will continue to promote the development of SoC technology from different levels.
SoC promotes the Development of computer Architecture
The development of SoC technology is closely related to the market demand. The main application fields of SoC are computer, communication, consumer electronics, industrial control, transportation and so on. Communications, computers and consumers account for more than 80 percent of SoC's sales, and the proportion of consumers is growing.
It can be divided into different categories if we further subdivide SoC market. For computer, there is image processing, hard disk drive, high-grade printer, personal assistant and so on. For communication, there is wired network, wireless network, mobile phone, visual equipment, communication base station and so on. For industrial control, there is process control or processing, test or instrument, medical equipment, monitoring system and so on. And for transportation, there is engine control, instrument device, safety system and so on. With the increasing scale of SoC market, it plays a more and more important role in the field of information technology and electronic products. At present, the SoC market is basically based on middle and low-grade SoC products. With the increasing demand for digital products, the demand for upmarket SoC is becoming more and more urgent. For example, in audio, video, communication and other fields, higher requirements are placed on SoC such as dual-core, quad-core and other multi-core integration. SoC will replace the traditional CPU in the middle and high grade to develop in the direction of better system performance, lower power consumption, lower cost, higher reliability and easier development in order to meet the interactive needs of people with GUI screen-centered multimedia interface and information terminals such as handwritten text input, identity recognition, voice dial-up Internet, sending and receiving e-mail, video playback, online games, videophone, language simultaneous interpretation and so on.SoC will embed enhanced processing devices such as 32-bit, 64-bit RISC chips or digital signal processing chips (DSP). At the same time, it supports the development of embedded RTOS and uses real-time multi-task programming technology and cross-development tool technology to control functional complexity to Inherit and develop computer processor technology. All of this poses greater challenges to computer architecture.
Under the guidance of computer architecture, SoC will usher in a new round of technical development. It takes embedded system application as the core, integrates software and hardware, and pursues the maximum inclusiveness of product system in system integration. SoC chip design not only needs strong background knowledge of computer architecture, but also highlights the status of software development, and puts forward higher requirements for development platform and embedded operating system. It provides a broad world for computer professionals to show their skills.
With the rapid development of processor / IP core design technology at home and abroad, it provides a powerful driving force for the development of computer architecture. Persisting in the development of processor core, core IP core and bus architecture with independent property rights, and ensuring compatibility, will make the development of SoC in China competitive thus driving the domestic IC industry to further develop. In order to meet the needs of industry, the of SoC designers’s in-depth researches on the architecture of configuration stream, instruction stream and data stream will also make a significant contribution to the development of computer science.
SoC opens up a new world for the development of interdisciplinary disciplines
SoC is a new field of technology that needs the support of many disciplines. Its development has been inseparable from the technical support from computer science, microelectronics, materials and technology, electronic communications and other fields. New technology and new products will continue to emerge and more in-depth researches on SoC are needed.
At present, the development of SoC technology is mainly realized at the same process level, mainly electronic technology. However, in practical applications, higher requirements for microminiaturization and system integration technology are constantly put forward. The development of micro-systems that integrate micro-mechanisms, micro-sensors, micro-actuators, signal processing and control and communication interface circuits and energy, which can perform specific functions, has put on the agenda. MEMS, which combines microelectronics and micromechanics, will become a new basis for the development of SoC. MEMS is also a multidisciplinary frontier research field, involving electronic engineering, mechanical engineering, material engineering, information engineering, physics, chemistry, optics, biomedicine and other disciplines and technologies.
The obvious advantage of system integration is to inherit and develop the benefits of various process technologies. Although the development of various processes is extremely unbalanced, SiP (System in Package) design technology can be used to integrate various integrated circuits of different processes such as CMOS circuits, GaAs circuits, SiGe circuits or optoelectronic devices, MEMS devices, and various passive components such as capacitors, inductors, etc. into a package when multiple processes are needed to coexist in the process of system integration. The implementation of more complex systems in a single package can improve packaging efficiency, performance and reliability by about 10 times, and the size and cost can be greatly reduced.
The development trend of SoC technology will be the integration of SoC, MEMS and SiP, and the computer architecture will be constantly enriched and developed. SoC's CDI classification model can depict the development of system technology, meet the single chip requirements of more complex systems and promote the interdisciplinary development at the same time.
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