Used to initiate and terminate pattern checking from this port. If pattern checking is not available from this port, Agent will report notSupported(1). Any SET attempts will be rejected. To check a bitstream, user should SET this object to start(3). To terminate checking, user should SET this object to stop(2). When read, Agent should report the value last SET. Agent may report stop(2) after a system reboot, or after it halts pattern checking because the time specified in nbsPrbsCheckDuration elapsed.