| This paper begins with the importance of VMS system in the ITS, then analyzes the functional characteristics of the VMS system, such as the diversification of communication, the flexible way of processing, etc. the entire design project of the VMS system and the difficulties, including control parts and display parts, the key technology in the process of design, such as the hardware design should avoid electromagnetic interference, the software design should consider the code performance, etc.At last, we designed the VMS system embedded controller using by Freescale MK60DN512ZVLQ10 processor and Xilinx’s FPGA, which is based on MQX OS. According to the Shanghai Hangzhou Ningbo VMS protocol, we focus on the embedded software. In this software development projects, there are 5 sub tasks, Display task, Adc task, Sdcard task, Watchdog task and Main task. Among them, the Main task is used for the completion of the protocol interaction between upper and lower computer; we use Display tasks for the data interaction between complete and FPGA, completing analytic playlist, and generating information on the screen; ADC task is mainly used for outer brightness information acquisition, so that the brightness of the screen can be adjusted; the Sdcard task is used to complete the SDHC device driver loading; The Watchdog task is to prevent the task to run fly. These 5 tasks are concurrent, every task is declared in the task template provided by MQX, which points the priority for every task and the size of the memory space. These tasks are concurrent execution, but there are also relationship between each other. Main task through a global flag whether it is set to zero control whether Display task is hanged. Whether Adc task performs automatic brightness adjustment depends on the frame data received from the host computer by Main task. The dynamic effect of the display depends on the interface of FPGA.All of the software code is written by C language, although C language has appeared in the 70s of last century, today, C language is still one of the most popular programming languages used all over the world. As a process oriented language, C language is easy to use, and its syntax is flexible.It is also other languages’ best introductory language, many of the underlying software is dependent on the C language, which is the reason that C language does not fade for a long time. Like other languages, C language itself provides a powerful function library, some common operations can be directly invoked by the C language library functions. C language has a pointer, which is a big feature of its existence, the presence of the pointer makes the C language can effectively access data address. On one hand, it can be more easily to operate on data. However, on the other hand, the use of the pointer should be very careful, it will lead to unforeseen results, if it is used improperly.At last, the advantages and disadvantages of the scheme design are introduced. Because of the way of serial communication between the controller and the screen, it has the advantages of simple operation, low bit error rate, but it also has low data transmission speed, short transmission distance and other disadvantages. For a large amount of data transmission, it should be considered the use of the network, if the geographical environment is complex, we can consider the way of wireless transmission. |
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