Posted 20 Dec 2010 22:05
In the computer, the Internet and the rapid development of communication technology at the same time, embedded systems development technology has made rapid development of embedded technology in the rapidly expanding range of applications. This paper describes a computer based on ARM and FP, high-speed Internet and communications technology development, embedded systems development technology has made rapid development of embedded technology in the rapidly expanding range of applications. In this paper based on ARM and FPGA, completely independent from software to hardware development multifunction vehicle bus (Multifunction Vehicle Bus) MVB embedded systems design and implementation. System design and implementation of general, an embedded system development process is as follows: determine the needs of embedded systems; design architecture of the system: Select the processor and related peripherals, operating system, development platform and hardware and software partitioning and overall system integration; detailed hardware and software design and RTL code, software code development; hardware and software together to reconcile integration; system testing. First, Step 1: Determine system requirements: typical of embedded systems is user-oriented, product-oriented, application-oriented, market application-oriented embedded system development and premise. An embedded system design depends on the system requirements. 1, MVB bus About TCN (Train Communication Network, referred to TCN) is a set of monitoring tasks within the whole trains, and information processing tasks in one of the train data communications IEC International Standard (IEC-61375-1), which includes two Wired Train Bus Bus types (WTB) and multi-car Bus (MVB). TCN in train control system with CAN bus status rather the position in automotive electronics. MVB Multifunction Vehicle Bus devices on the train for transfer and exchange of data between the standard communication medium. Additional equipment on the bus may be in the function, size, performance, distinct, and the MVB bus, but they are connected, through the MVB bus to exchange information, form a complete communication network. In the MVB system, according to IEC-61375-1 Train Communication Network standard, MVB bus has the following characteristics: topology: MVB bus structure follows OSI model, drawing on ISO standards. Supports up to 4,095 devices from a central control of the bus manager. Simple sensors and intelligent co-exist on the same bus station. Data Type: MVB bus supports three data types: a. process data: the state of process variables that the train, such as speed, motor current, the operator's command. Process is called the process variable data. Their transmission time is defined and bounded. To ensure that this delay time, the data is periodically transmitted. b. message data: the message is divided into small packets, these packets were numbered by the destination station confirmation. Message packet and control data associated with the formation of the message data. Message data transmitted by the command. Function message is used by the application layer; service message for the train communication management system itself. c. monitoring data: a short frame, the main equipment for the same bus with its equipment in the state of validation, on-line testing equipment, sovereignty transfer, the early train operation and other management functions. Media interviews: MVB bus supports RS485 copper and fiber media. The physical layer of the data format is 1.5Mbps serial Manchester encoded data. MVB media access BA from the bus manager to manage the bus manager BA is the only bus master, all other devices are slaves. Master the order in accordance with a predetermined periodic port polling interval in the cycle, the master turned to deal with sporadic requests. Reliability measures: MVB integrity of fault-tolerant measures include sending: link layer has an expansion of the error detection mechanism, which provides the hamming distance is 8 bits can be detected, frame and synchronization errors. Independence of failures: the media is often full of copper double configuration to ensure the independence of equipment failure. Send availability: the availability of redundant through media, power redundancy, management, redundancy and other measures can be improved. 2, MVB system's basic requirements are as follows: a. full and IEC-61375-1 (TCN) is compatible with international standards to support the MVB bus, three data types defined by process data, message data, monitoring data. b. the system can be configured to: i. Bus Manager (BA) function ii. Bus Manager (BA) functions and communication functions iii. independent communications functions using ARM7TDMI processor c. d. e. for real-time operating system TCN real-time protocol stack (RTP) f. support the process of logical port data in 4096 to support and host PC104 g. dual port RAM interface to the host input voltage 5V i. h. Operating temperature: -40 ?~ 75 ?3, other MVB Multifunction Vehicle Bus system needs the user's train control system with the synchronous design, has a strict time limit. Second, the Step 2: design system architecture, co-allocation of hardware / software requirements of embedded systems include hardware and software of two parts: the hardware architecture of embedded processors as the center, configuration memory, I / O devices, communication modules and other necessary peripherals; software components to software development platform as the ****, up to provide application programming interface (API), down to specific hardware features shielded Board Support Package BSP. Embedded systems, software and hardware work closely with and coordinate the work together to complete the system intended function. According to OSI seven-layer model can determine the link layer and physical layer consists of hardware, the other layers by the software, as shown in Figure 1. Figure 1: MVB of the OSI model and the MVB system software and hardware division 1, the embedded operating system options: Generally speaking, for an embedded system, select the operating system to consider the following factors: the microprocessor operating system support operating systems performance of the operating system software components and device drivers the operating system debugging tools, development environments, Circuit Emulator (ICE), compiler, assembler, linker, debugger and simulator compatibility, and so the standard operation of the operating system technical support system is to provide the level of the operating system source code or object code of the operating system operating system license usage status of the developer's reputation more than the system needs and the principle of the system used in the MVB Vxworks real-time operating system, VxWorks, wind River (Windriver) development of real-time operating systems in the world, with its excellent reliability, and real-time kernel can be reductive, is widely used in telecommunications, military, aerospace, aviation, industrial control and other key industries, the development environment for the Tornado. 2, processor choice: the choice processor for embedded systems need to consider the following aspects: performance: the performance of the processor must have sufficient mandate and support the product life cycle. Tool Support: Support software to create, debug, system integration, code tuning and optimization tools to the overall success of the project is critical. Operating system support: embedded system applications require use of abstraction helps to reduce its complexity. Developers processor past experience: a processor or processor family of products can reduce the considerable development experience to learn new processors, tools and techniques of the time. Cost, power consumption, time to market, technical support, etc. in the system design, Taking all these factors, taking into account the performance of the processor, operating system support and train the harsh industrial environment, etc., in the MVB system ATMEL selected industrial areas for industrial control the AT91 series of ARM processor-level AT91M40800, it is based on the ARM7TDMI ****, containing high-performance 32-bit RISC processor, highly integrated 16-bit instruction set, 8KB on-chip SRAM, programmable external bus interface (EBI), 3-channel 16-bit counter / timers, 32 programmable I / O port, interrupt controller, 2 USART, programmable watchdog timer, the master clock circuit and the DRAM timing control circuit, and is equipped with advanced energy-saving circuit; also supports JTAG debugging, clocked up to 40MHz.