Asynchronous Hard Real Time Signals Transmission in Embedded Networks

Abstract

Nowadays in the aerospace industry the router-based onboard embedded networks gradually replacing bus-based networks because they are already not satisfy the aerospace performance requirements. The SpaceWire, GigaSpaceWire and SpaceFibre standards are developing to meet the increasing aerospace requirements. The important requirement for any aerospace embedded onboard network is a transmission of control information and system signals in hard real time. These signals can be synchronous and asynchronous, periodic and aperiodic, with or without acknowledges. The distributed interrupt mechanism is used for asynchronous signal transmission and it is included into the second edition of SpaceWire standard. The Time-code propagation mechanism is used for synchronous signal transmission in SpaceWire. The broadcast messages mechanism is used for transmission of different system signal in SpaceFibre but it does not quite meet the requirements of hard real time. In this paper the authors consider the asynchronous signals transmission with and without acknowledges. The aims of this paper are following: 1) theoretically investigate the distributed interrupt mechanism; 2) to prove its properties; 3) to specify parameters and limitations; 4) to derive the time characteristics. For these purpose the authors developed the analytical model which describe the distributed interrupt propagation mechanism in terms of the graph theory.