Description

The AS8202NF communication controller is an integrated device supporting serial communication according to the TTP specification version 1.1. It performs all communication tasks such as reception and transmission of messages in a TTP cluster without interaction of the host CPU. TTP provides mechanisms that allow the deployment in high-dependability distributed real-time systems. It provides the following services:

• Predictable transmission of messages with minimal jitters
• Fault-tolerant distributed clock synchronization
• Consistent membership service with small delay
• Masking of single faults

The CNI (communication network interface) forms a temporal firewall. It decouples the Controller network from the host subsystem by use of a dual ported RAM (CNI). This prevents the propagation of control errors. The interface to the host CPU is implemented as a 16-bit wide non-multiplexed asynchronous bus interface. TTP follows a conflict-free media access strategy called time division multiple access (TDMA). This means, TTP deploys a time slot technique based on a global time that is permanently synchronised. Each node is assigned a time slot in which it is allowed to perform transmit operation. The sequence of time slots is called TDMA round, a set of TDMA rounds forms a Cluster cycle. The operation of the network is repeated after one cluster cycle. The sequence of interactions forming the cluster cycle is defined in a static time schedule called message descriptor list (MEDL). The definition of the MEDL in conjunction with the global time determines the response time for a service request.