Dynamic replacement of software in hard real-time systems

software system may threaten the mission success. The usual maantenance technaques are not useful when dealang wzth non-stop software systems. It as not 0 Typical telecommunication systems require conpossable to stop the system executaon to update some tinuous operation, in order to provide an adeof zts components. Dynamac software replacement as quate service. The fault-rate of these systems a mechanasm that allows components iipdataiig waihout should be few hours in a year. stopping the wh,ole system. Several systems architectures and protocols for dyn,amically replacing software components have been developed. However, none of them takes inlo acc0un.t the specific requirements of embedded hard real-time system,s. In particular, there is no provision to en.sure that the timing requirem,ents will be met during and after a replacement operation. In, this paper, a protocol for dynamic replacement of software components in embedded hard real-time is described. This protocol does not disturb the real-time processes, so they can meet iheir deadliiies. The replncem,eiji operation. is m,an.aged by a Replacement. Supervisor that is implemented as a sporadic semer ,with a limited time budget. The protocol as divided into four p h, ases : loa ding, creation,, rep1 a ce in en, d a ii. d clea, n. in g .