Design Of Multi-function Vehicle Bus Interface Card

MVB Interface Card is an important communication device of train communication network which connect different types of buses, implement conversion of protocols and transfer inter-bus data by software running in the card.This paper analyses the software structure, and divide the software into three parts: initialize module, Real Time Protocol (RTP), CAN application in which RTP is emphasis. RTP consists of two parts: process data service and message data service. This paper analyses two design difficulties: Link layer interface module and message module design. Link layer interface module design factor is shared memory design. Shared memory is between link layer and RTP which storing process data and message packet. The key factor of shared memory design is how to aceess it parallely by CPU and MVB moudle. It revolved the alternation and data transfer which affect to stability and reliability of the whole system. So it is the keystone and difficulty of the project. The shared memory design has two points: first, it must satisfy MVB module's accessing demand of memory; this must be the highest priority. Second, it must satisfy the integrity of process data accessing by CPU. This paper abandoned the CPU-wait method, using single SRAM and designing appropriate timing to implement link layer data reading and write FIFO to implement link layer data writing. Lots of experiment proved that this idea primely meets the protocol's requirement. The message module has session layer, transport layer and network layer. In this paper, the author designed data structure and state machine for session layer; desined issue state machine and time-out machine for transport layer; dividing network layer into two tasks: sending task and routing task. Based of the functions, the message module is divided into different tasks and interfaces.Until now, the development is completed. The card is connected with various MVB slave devices, and the project is checked and accepted favorably. The software work steady and achieved the anticipate goals.