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Dynamic software updates enable software evolution and bug fixes to embedded systems without disrupting their run-time operation. Scheduling dynamic updates for safety-critical embedded systems, such as aerial drones, must be done with great care. Otherwise, the system's control loop will be delayed leading to a partial or even complete loss of control, ultimately impacting the dependable operation. We propose an update scheduling algorithm called NeRTA, which schedules updates during the short times when the processor would have been idle. NeRTA consequently avoids the loss of control that would occur if an update delayed the execution of the control loop. The algorithm computes conservative estimations of idle times to determine if an update is possible, but is also sufficiently accurate that the estimated idle time is typically within 15% of the actual idle time. |
