In modern embedded platforms, safety-critical functionalities that must be certified correct to very high levels of assurance may co-exist with less critical software that are not subject to certification requirements. One seeks to satisfy two, sometimes contradictory, goals upon such mixed-criticality platforms: (i) certify the safety-critical functionalities under very conservative assumptions, and (ii) achieve high resource utilization during run-time, when actual behavior does not live up

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... the pessimistic assumptions under which certification was made. This paper describes efforts at designing fixed-priority scheduling algorithms that balance these two requirements, when scheduling recurrent tasks that are triggered by external events of unknown exact frequency.