Optimising the General Purpose Controller Network Architecture (GPCNA)

General Purpose Controller Network Architecture (GPCNA) is an experimental network architecture designed for interconnecting nodes in distributed embedded applications. GPCNA provides deterministic access to the network medium to support distributed hard real-time application components. GPCNA uses a token bus to transfer fixed sized frames. Token monitor issues an explicit token that contains the schedule using which the nodes are allotted medium access. The 37 byte frame structure includes a 5 byte header and a 32 byte payload. Payload within the token carries single byte addresses of the nodes on the network sorted in the order they are granted access to the medium. Only the node in possession of the token is granted medium access, and this node subsequently transmits the token to the node scheduled next in the token payload. Thus, the original GPCNA allows only up to 32 nodes to be present on the network. This paper suggests three optimizations to the original GPCNA concept. Primarily, the use of virtual tokens reduces the token overhead. Nodes can dynamically request bandwidth allocation to transmit a periodic or sporadic message. Finally, categorization of nodes as talkers and listeners and use of different schedules for successive transmission cycles increases the number of nodes on the GPCNA bus.