Cegelec

Jozef Dworzecki

A method of scheduling tasks subject to timing and succession constraints essentially comprises grouping the tasks in layers according to succession constraints and scheduling the tasks layer by layer in increasing layer order up to the last layer, if possible, and then deciding that the resulting scheduling succeeds. If the scheduling achieved in a layer other than the first layer does not satisfy one or more constraints applying to a task belonging to the current layer, the method reschedules a layer containing a predecessor task corresponding to an unsatisfied constraint, schedules or reschedules all the other layers higher than the layer of the predecessor task, up to the last layer, if possible, and then decides that the resulting scheduling succeeds. Applications include scheduling of transmission of information on an industrial data bus.

Method of scheduling successive tasks

A method of scheduling successive tasks subject only to timing constraints calculates for each task upper and lower limits of the interval in which execution of that task must start. It then constructs a first series in which all the tasks are scheduled in increasing order of their lower limit and a second series in which all the asks are scheduled in increasing order of their upper limit, before constructing an initial permutation by scheduling all the tasks in the order of the first series and verifying if the initial permutation satisfies all the constraints. If not all the constraints are satisfied, the method determines in the initial permutation the first ill-placed task for which a constraint is not satisfied and a candidate task in the second series immediately preceding the ill-placed task in the second series in the current permutation. It then verifies that if the candidate task is shifted in the current permutation to a position immediately after the ill-placed task all the constraints applying to all the tasks shifted in this way are then satisfied.

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Fontenay le Fleury, France

Jozef Dworzecki