In an operation scheduler adapted to schedule in an asynchronous contention-based system a first FIFO queue is adapted to store one trigger message or one operation request. A message router is coupled to the first FIFO queue and is adapted to route instructions to a second FIFO queue or a memory and locate in the memory the instructions of a suspended operation associated with a trigger message and authorize execution of the suspended operation. An arbitration unit is coupled to the second FIFO queue and to the memory, and is adapted to schedule the execution of instructions associated with a standalone non-preemptable operation during a period of time within which at least one operation of the first sequence is being suspended.