工业实时通讯网络 (现场总线) 的基础理论研究与现状 (下)

现场总线的实时能力是分布式计算机系统实时 性能的根本保证．围绕这一主题，作者详细地论述了如何利用现场总线来支持实时通信．在 上一篇，作者从多个方面对有关现场总线的实时能力进行了全面的阐述．在本篇，作者从MA C层协议的时态特征入手对FF和WorldFIP的实时能力进行了细致的分析，并且针对协议中的 缺陷提出了改进方案．FF和WorldFIP均明确区分周期信息和非周期信息，并且利用集中式 令牌和分布式管理这两类信息．为了充分利用这两类令牌，作者对调度表的结构和规模、调 度算法及其可调度性分析、令牌运行周期的设定等方面的研究进展和未来研究进行了详细阐 述．最后，通过分析工业应用对实时的实际要求，作者提出采用实时服务质量来建立统一 的性能评价体系，来克服现有方法的局限性．

SURVEY OF REAL-TIME SCHEDULE THEORY AND THE STATE-OF- THE-ART OF ITS APPLICATION IN INDUSTRIAL REAL-TIME COMMUNICATION SYSTEM (PART TWO)

The realtime performance of distributed computer system (DCS) is guaranteed by realtime capability of fieldbus, that is why authors focus on how utilizing fieldbus to meet realtime requirement of tasks in DCS. In last paper, authors do global analyzing realtime capability of fieldbus on many aspects. In this paper, the authors primarily analyze realtime capability of FF and WorldFIP from their MAC protocol in detail and propose the improved methods for the found deficiency in the MAC protocol. FF and WorldFIP both explicitly distinguish periodic and aperiodic messages and support them with centralized token and distributed token. For effectively utilizing the two kinds of token, the authors investigate concerned problems deeply, such as construction and size of schedule table,schedule algorithm and algorithm schedubility, setting of parameter of e do PT token operation period. Further, the authors proposes general performance evaluation architecture for computers network through realtime quality of service, after investigating the actual temporal requirement of industry applications.