Device Development Board SMT Assembly

     The development board is a circuit board used for embedded system development, including a series of hardware components such as central processing unit, memory, input device, output device, data path/bus and external resource interface. Development boards are generally customized by embedded system developers themselves according to development needs, and can also be researched and designed by users themselves. The development board is for beginners to understand and learn the hardware and software of the system. At the same time, some development boards also provide the basic integrated development environment, software source code and hardware schematic diagram. Common development boards include 51, ARM, FPGA, and DSP development boards. In addition to integrating CPU, FPGA, DSP, etc., the development board also needs a relatively complete input and output interface, such as keyboard and LCD, program download interface, memory (RAM), FlashROM, power supply module, etc.

Basic overview

    The development board (demoboard) is a circuit board used for embedded system development, including a series of hardware components such as central processing unit, memory, input device, output device, data path/bus and external resource interface. In the general embedded system development process, the hardware is generally divided into two platforms, one is the development platform (host), and the other is the target platform (target), that is, the development board. The development platform described here refers to using a computer to connect to the target platform through a transmission interface, such as a serial port (RS-232), USB, parallel port, or network (Ethernet).

    Development boards are generally customized by embedded system developers themselves according to development needs, and can also be researched and designed by users themselves. The development board is for beginners to understand and learn the hardware and software of the system. At the same time, some development boards also provide the basic integrated development environment, software source code and hardware schematic diagram. Common development boards include 51, ARM, FPGA, and DSP development boards.

Selection requirements

      For embedded system development, you must first select the type of CPU, FPGA, and DSP that meet your own development needs, and then select the range of development boards that support the selected chip according to the selected type of CPU, FPGA, and DSP. Again, the ability and level of the development environment and technical support provided by the development board are preferred. Finally, it is necessary to consider that in addition to integrating CPU, FPGA, DSP, etc., the development board also needs a relatively complete input and output interface, such as keyboard and LCD, program download interface, memory (RAM), FlashROM, power supply module, etc. At the same time, for the convenience of debugging at the initial stage of development, several special pins, such as JTAG interface, USB and serial ports, will be drawn out for use by external debugging modules.

Development Migration

     After the hardware and specifications are selected, the next step is to enter the initial system development and establish an open environment. If the embedded operating system used in the project is not developed by itself, but purchased from other manufacturers, most of them provide an integrated development environment (IDE) and an emulator (Emulator) so that developers can speed up the entire development process. When you get the operating system that has been transplanted by the system manufacturer, and you have confirmed that you have provided sufficient relevant information, you can perform integration actions for your target platform.

     After the operating system is selected, the various development tools used on the development platform are usually specified, such as compilers, linkers, etc. The compilation parameters that need to be set during development will vary according to each environment. This part must compile an executable image file according to the hardware specifications and instructions, and then burn it to the target platform through the burning tool.

Development board classification

single chip microcomputer

① 51 series MCU

     51 There are many types of single-chip microcomputers. 8031/8051/8751 are the early products of Intel, while AT89C51 and AT89S52 of ATMEL are more practical. The 51 series of ATMEL company also has AT89C2051, AT89C1051 and other varieties. These chips are simplified versions formed after some functions are simplified on the basis of AT89C51. The currently available chips in the market include ATMEL's 51 and 52 chips, HYUNDAI's GMS97 series, WINBOND's 78e52, 78e58, and 77e58.

② PIC series MCU

     All over the world, PIC microcontrollers can be widely used in various fields from computer peripherals, home appliance control, telecommunications, smart instruments, automotive electronics to financial electronics. The PIC series single-chip microcomputer is divided into: basic series, such as PIC16C5X, which are suitable for the selection of various household appliances with strict cost requirements; intermediate series, such as PIC12C6XX, which have high performance, such as internal A/D converter, E2PROM data memory, comparator output, PWM output, I2C and SPI interfaces; PIC intermediate series products are suitable for the design of various high, medium and low-end electronic products. Advanced series, such as PIC17CXX, have rich I/O control functions, and can be externally extended with EPROM and RAM, and are suitable for use in high-end and mid-range electronic equipment.

③ AVR series MCU

     AVR single-chip microcomputer is an enhanced RISC (Reduced Instruction Set CPU) with built-in Flash developed by ATMEL in 1997. It is a high-speed 8-bit single-chip microcomputer with reduced instruction set. AVR's single-chip microcomputer can be widely used in various fields such as computer peripheral equipment, industrial real-time control, instrumentation, communication equipment, and household appliances.

④ ARM development board

    The ARM development board is an embedded development version of the ARM core chip, including ARM7, ARM9, ARM11, Cortex-M, Cortex-A, and Cortex-R. Documentation is unified and facilitates development. At present, chips including ATMEL, NXP, ST, and Freescale have launched chips based on ARM cores and corresponding development boards.

CPLD/FPGA

     CPLD (Complex Programmable Logic Device) complex programmable logic device is a device developed from PAL and GAL devices. It is relatively large in scale and complex in structure, and belongs to the scope of large-scale integrated circuits. It is a digital integrated circuit in which users can construct logic functions according to their own needs. The basic design method is to use the integrated development software platform to generate corresponding target files by means of schematic diagrams and hardware description languages, and transmit the code to the target chip through the download cable ("in-system" programming) to realize the designed digital system. .

Many companies have developed CPLD programmable logic devices today. The typical ones are the products of Altera, Lattice, and Xilinx, the world's three authoritative companies. Here are the commonly used chips: Altera EPM7128S (PLCC84), Lattice LC4128V (TQFP100), Xilinx XC95108 (PLCC84)

    FPGA is the abbreviation of Field-Programmable Gate Array in English, that is, Field Programmable Gate Array, which is a product of further development on the basis of programmable devices such as PAL, GAL, and CPLD. It emerged as a semi-custom circuit in the field of application-specific integrated circuits (ASIC), which not only solves the shortcomings of custom circuits, but also overcomes the shortcomings of the limited number of original programmable device gates.

    At present, there are many varieties of FPGA, such as XC series of XILINX, TPC series of TI company, FIEX series of ALTERA company, etc.

DSP

    DSP (digital signal processor) is a unique microprocessor, a device that processes a large amount of information with digital signals. Its working principle is to receive an analog signal, convert it into a digital signal of 0 or 1, then modify, delete, and strengthen the digital signal, and interpret the digital data back to analog data or the actual environment format in other system chips. Not only is it programmable, but its real-time running speed can reach tens of millions of complex instruction programs per second, far exceeding that of general-purpose microprocessors. It is an increasingly important computer chip in the digital electronics world. Its powerful data processing capability and high operating speed are the two most commendable features.

    At present, the mainstream DSP chips mainly include TI 2000 series, TI 5000 series, TI6000 series and ADI DSP series of ADI Company.

ARM

    ARM, the abbreviation of Advanced RISC Machines, is a general term for a class of microprocessors. ARM is also a well-known company in the microprocessor industry, and has designed a large number of high-performance, cheap, and low-power RISC processors, related technologies and software. The technology is characterized by high performance, low cost and low energy consumption. Applicable to a variety of fields, such as embedded control, consumer/educational multimedia, DSP and mobile applications.

    At present, the mainstream of ARM is divided into the following categories:

    ARM7TDMI used in Game Boy Advance, Nintendo DS, iPod

    ARM9TDMI Armadillo, GP32, GP2X (first core), Tapwave Zodiac (Motorolai. MX1); GP2X (second core)

    ARM9E Nintendo DS, NokiaN-GageConexant 802.11 chips; ST Micro STR91xF,

    ARM11 Nokia N93, Zune, Nokia N800, NOKIA E72

    Cortex Texas Instruments OMAP3; Broadcom is a user; Luminary Micro family of microcontrollers

MIPS

     MIPS is a very popular RISC processor in the world. MIPS means "Microprocessor without interlocked piped stages" (Microprocessor without interlocked piped stages), its mechanism is to use software methods to avoid data-related problems in the pipeline as much as possible.

MIPS was first developed in the early 1980s by a research group led by Professor Hennessy of Stanford University. The R series of MIPS is the microprocessor of RISC industrial products developed on this basis. These series of products are used by many computer companies to form various workstations and computer systems.

     It can be said that MIPS is the best-selling RISC CPU. From anywhere, such as Sony, Nintendo game consoles, Cisco routers and SGI supercomputers, MIPS products can be seen on sale. Compared with Intel, the authorization fee of MIPS is relatively low, so it is adopted by most chip manufacturers except Intel. Afterwards, MIPS changed its strategy and began to focus on embedded systems, and successively developed a high-performance, low-power 32-bit processor core (core) MIPS324Kc and a high-performance 64-bit processor core MIPS64 5Kc. In 2000, MIPS released a version for MIPS32 4Kc and a 64-bit MIPS 64 20Kc processor core.

     The MIPS32 4KcTM processor is a high-performance, low-voltage 32-bit MIPS RISC core designed specifically for System-On-a-Chip using MIPS technology.

     MIPS 64 20Kc has a strong floating-point capability and can form different systems, from Octane workstations with one processor to Origin 2000 servers with 64 processors; this CPU is more suitable for graphics workstations. The latest MIPS R12000 chip has been applied in SGI's server, and its main frequency can reach up to 400MHz at present.

     MIPS K series microprocessors are currently one of the most used processors after ARM (MIPS was the most used processor in the world before 1999), and its application fields cover game consoles, routers, laser printers, handheld computers, etc. In addition to a very small proportion of applications in mobile phones, MIPS has achieved quite good results in the general digital consumption, Internet voice, personal entertainment, communication and business application markets. And its most widely used should be home audio-visual appliances (including set-top boxes), Netcom products, and automotive electronics.

PPC

     PowerPC is a central processing unit (CPU) with a reduced instruction set (RISC) architecture. Its basic design comes from IBM (International Business Machines Corporation)'s POWER (Performance Optimized With Enhanced RISC; "IBM Connect Newsletter" 2007 8 Yuehao translated as "enhanced RISC performance optimization") architecture. In the 1990s, IBM (International Business Machines Corporation), Apple (Apple Corporation) and Motorola (Motorola) successfully developed PowerPC chips and manufactured multiprocessor computers based on PowerPC. The PowerPC architecture is characterized by good scalability, convenience and flexibility.

     PowerPC processors come in a wide range of implementations, from high-end server CPUs like the Power4 to the embedded CPU market (Nintendo Gamecube uses PowerPC). The PowerPC processor has a very strong embedded performance because of its excellent performance, low power consumption and low heat dissipation. Apart from integrated I/O like serial and Ethernet controllers, this embedded processor differs quite significantly from a "desktop" CPU. For example, the 4xx series of PowerPC processors lacked floating-point arithmetic and also used a software-controlled TLB for memory management rather than inverted page tables as in desktop chips.

Hardware driver

      Most embedded hardware requires some type of software for initialization and management. Software that interacts directly with and controls a piece of hardware is called a device driver. All embedded systems that require software require device driver software at their system software layer. Device drivers are software libraries that initialize hardware. They manage the access of high-level software to hardware. It is the link between hardware and operating systems, middleware and application layers. Specifically, such drivers include host processor architecture-specific functional drivers, memory and memory management drivers, bus initialization and transaction drivers, and board-level and host-CPU-level I/O initialization and Control drivers (such as for networking, graphics, input devices, storage devices, debug I/O, etc.).

      Device drivers are usually divided into architecture-specific device drivers and generic device drivers. Architecture-specific device drivers manage hardware embedded in the main processor (architecture). Architecture-specific drivers are responsible for initializing components within the host processor. Examples of such drivers include drivers for on-chip memory, integrated memory managers (MMUs), and floating-point hardware. Generic device drivers manage hardware on the board as well as hardware that is not integrated into the main processor. In a generic device driver, a portion of the architecture-specific source code is usually included, because the main processor is the central control unit, and access to any component on the board usually goes through the main processor. However, a generic driver can also manage board-level hardware that is not dedicated to a particular processor, which means that a generic driver can be configured for use on many architectures, as long as the architecture contains the hardware for which the driver corresponds. . The generic driver contains code that initializes and manages access to the remaining major components on the board, including board-level buses (I2C, PCI, PCMCIA, etc.), off-chip memory (controller, level 2+ cache, flash, etc.) ) and off-chip I/O (Ethernet, RS-232, display, mouse, etc.).

Component

Embedded microprocessor

      The core of the hardware layer of the embedded system is the embedded microprocessor. The biggest difference between the embedded microprocessor and the general-purpose CPU is that most of the embedded microprocessors work in a system specially designed for a specific user group. The completed tasks are integrated inside the chip, which is conducive to the miniaturization of the embedded system design, and also has high efficiency and reliability.

      The architecture of the embedded microprocessor can adopt Von Neumann architecture or Harvard architecture; the instruction system can choose Reduced Instruction Set Computer (RISC) and complex instruction system CISC (Complex Instruction Set Computer, CISC). The RISC computer only includes the most useful instructions in the channel to ensure that the data channel executes each instruction quickly, thereby improving the execution efficiency and making the CPU hardware structure design easier.

       Embedded microprocessors have various systems, even in the same system, they may have different clock frequencies and data bus widths, or integrate different peripherals and interfaces. According to incomplete statistics, there are more than 1,000 embedded microprocessors in the world at present, and there are more than 30 series of architectures, among which the mainstream systems are ARM, MIPS, PowerPC, X86 and SH. But different from the global PC market, there is no embedded microprocessor that can dominate the market. In terms of 32-bit products, there are more than 100 embedded microprocessors. The choice of embedded microprocessor is determined according to the specific application.

Memory

     Embedded systems require memory to store and execute code. The memory of embedded system includes Cache, main memory and auxiliary memory.

     Cache is a memory array with small capacity and high speed. It is located between the main memory and the embedded microprocessor core, and stores the program codes and data that the microprocessor uses most recently. When a data read operation is required, the microprocessor reads data from the Cache as much as possible instead of reading from the main memory, which greatly improves the performance of the system and improves the connection between the microprocessor and the main memory. data transfer rate. The main goal of Cache is to reduce the memory access bottleneck caused by memory (such as main memory and auxiliary memory) to the microprocessor core, so that the processing speed is faster and the real-time performance is stronger. In the embedded system, Cache is all integrated in the embedded microprocessor, which can be divided into data Cache, instruction Cache or mixed Cache, and the size of Cache depends on different processors. Generally, mid-to-high-end embedded microprocessors will integrate Cache.

     The main memory is a register that the embedded microprocessor can directly access, and is used to store programs and data of the system and users. It can be located inside or outside the microprocessor, and its capacity is 256KB~1GB, depending on the specific application. Generally, the on-chip memory has a small capacity and fast speed, and the off-chip memory has a large capacity. Memories commonly used as main memory include: ROM NOR Flash, EPROM, and PROM. RAM type SRAM, DRAM and SDRAM, etc. Among them, NOR Flash has been widely used in the embedded field due to its advantages of high rewritable times, fast storage speed, large storage capacity, and low price.

Auxiliary memory

      Auxiliary memory is used to store program codes or information with a large amount of data. It has a large capacity, but its reading speed is much slower than that of main memory, and it is used to store user information for a long time.

      Commonly used external storage in embedded systems are: hard disk, NAND Flash, CF card, MMC and SD card, etc.

Common interface

      The interaction between the embedded system and the outside world requires a certain form of general-purpose device interface, such as A/D, D/A, I/O, etc. The peripherals realize the input/output of the microprocessor by connecting with other off-chip devices or sensors Function. Each peripheral usually has only a single function, which can be on-chip or off-chip. There are many types of peripherals, ranging from a simple serial communication device to a very complex 802.11 wireless device.

      At present, the general equipment interfaces commonly used in embedded systems include A/D (analog/digital conversion interface), D/A (digital/analog conversion interface), and I/O interfaces include RS-232 interface (serial communication interface), Ethernet (Ethernet Interface), USB (Universal Serial Bus Interface), Audio Interface, VGA Video Output Interface, I2C (Field Bus), SPI (Serial Peripheral Interface) and IrDA (Infrared Interface), etc.

Status and Trends

     The information age and the digital age have given embedded products a huge opportunity for development, showing a bright future for the embedded market, and at the same time posing new challenges to embedded manufacturers. From this, we can see the future of embedded systems. Major development trend:

     1. Embedded development is a system engineering, so embedded system manufacturers are required not only to provide the embedded software and hardware system itself, but also to provide powerful hardware development tools and software package support.

     At present, many manufacturers have fully considered this point. While promoting the system, they also focus on promoting the development environment. For example, while promoting Arm7 and Arm9 chips, Samsung also provides development boards, version and support package (BSP), and WindowCE also provides Embedded VC++ as a development tool when the main system is promoted, as well as the Tonado development environment of Vxworks and the Limda compilation environment of DeltaOS. etc. are typical manifestations of this trend. Of course, this is also the result of market competition.

     2. With the maturity of Internet technology and the improvement of bandwidth, the requirements of networking and informatization have made the single-function devices in the past, such as telephones, mobile phones, refrigerators, microwave ovens, etc. no longer have single functions, and the structures have become more complex.

      This requires chip design manufacturers to integrate more functions on the chip. In order to meet the upgrade of application functions, designers use more powerful embedded processors such as 32-bit and 64-bit RISC chips or signal processors DSP to enhance processing. At the same time, increase the functional interface, such as USB, expand the bus type, such as CAN BUS, strengthen the processing of multimedia, graphics, etc., and gradually implement the concept of system on chip (SOC). In terms of software, real-time multi-task programming technology and cross-development tool technology are used to control functional complexity, simplify application program design, ensure software quality and shorten development cycle. Such as HP

      3. Network interconnection has become an inevitable trend.

      In order to adapt to the requirements of network development, future embedded devices must provide various network communication interfaces on the hardware. The traditional single-chip microcomputer has insufficient support for the network, and the new generation of embedded processors has begun to embed the network interface. In addition to supporting the TCP/IP protocol, some support one of the communication interfaces of IEEE1394, USB, CAN, Bluetooth or IrDA or There are several types, and corresponding communication networking protocol software and physical layer driver software are also required. In terms of software, the system kernel supports network modules, and can even embed a web browser on the device, so that it can truly use various devices to surf the Internet anytime, anywhere.

        4. Simplify the system core, algorithm, reduce power consumption and hardware and software costs.

Embedded products in the future are devices that are closely integrated with hardware and software. In order to reduce power consumption and cost, designers need to simplify the system core as much as possible, keep only hardware and software closely related to system functions, and use the lowest resources to achieve the most appropriate functions. Designers are required to select the best programming model and continuously improve algorithms to optimize compiler performance. Therefore, not only software personnel are required to have rich hardware knowledge, but also need to develop advanced embedded software technologies, such as Java, Web and WAP.

        5. Provide a friendly multimedia man-machine interface

The most important factor for an embedded device to be in close contact with users is that it can provide a very friendly user interface. Graphical interface and flexible control methods make people feel that the embedded device is like a familiar old friend. This requirement makes the embedded software designers have to work hard on the graphical interface and multimedia technology. Handwritten text input, voice dial-up, Internet access, sending and receiving e-mails, and colorful graphics and images will all make users feel free. At present, some advanced PDAs have realized the writing of Chinese characters and voice release of short messages on the display screen, but there is still a long way to go for ordinary embedded devices.