A position-based scheduling capability supports interaction between one or more user applications and a scheduler for performing testing via a scan chain of a unit under test. The scheduler receives access requests from one or more user applications, where each access request is a request for access to a segment of the scan chain, respectively. The scheduler determines scheduling of the access requests using a circuit model configured to represent an ordering of the segments of the scan chain. The scheduler may provide the access responses to the user application(s) from which the access requests are received, thereby enabling the user application(s) to issue test operations toward a processor configured to generate test data to be applied to the scan chain. The scheduler may obtain the test operations and send the test operations toward a processor configured to generate test data to be applied to the scan chain.