Methods for equitable distribution of bus access among nodes of Controller Area Network

Abstract

Controller Area Network (CAN) is the dominant network in automotive applications and is making inroads in the industrial and medical environments too. The basic CAN protocol suffers an inherent shortfall that it starves low priority nodes to transmit data due to its fixed priority (FP) scheme. The paper proposes implementation of two priority schemes to mitigate the same. In the first scheme, that implements Round-Robin(RR) priority, the access to the bus is given in cyclic fashion. Thus, giving opportunity for lower priority nodes to transmit. In the second scheme, that implements Least Recently Used (LRU) priority, priorities of the nodes are rotated depending on node's recent access of the bus, thereby giving equal opportunity to all the nodes for accessing the bus. Proposed schemes therefore give provisions to change fixed priority scheme of CAN protocol into Round-Robin and Least Recently Used (LRU) priority schemes respectively. Also, the proposed RR and LRU priority schemes can coexist with FP scheme. The proposed schemes are applied at every node which avoids the use of any explicit master node or message scheduler to provide equal opportunity to all the nodes. The proposed schemes do not require changes at physical and data-link layers of CAN protocol. Consideration of emergency state for a particular node is another small contribution of this paper. The proposed emergency priority scheme allows particular nodes to have provision of emergency states for gaining access to the bus out of turn. A software simulation of proposed schemes in LabVIEW verify equitable access to nodes.