Method and structure for automated switching between multiple contexts in a storage subsystem target device

摘要

In a storage target device controller capable of managing multiple command contexts, methods and associated apparatus are provided for automatically managing the plurality of contexts using a state machine model. The state machine model is operable on a target device controller having an active context register set for processing of the presently active transfer on the host channel and an inactive context register set for storing an inactive context. The active context register set and inactive context register set are rapidly and automatically swapped by operation of the state machine model to resume or start processing of an inactive context. Additional inactive contexts are stored in a buffer memory associated with the target device controller. The inactive context register set is automatically stored into a selected one of the additional inactive contexts or loaded from a selected one of the additional inactive contexts by operation of the state machine model of the present invention. The state machine model performs appropriate swap, load, and store operations for contexts in accordance with priorities to improve performance of the target device. The highest priority is an auto-write context corresponding to a write command for which data will be imminently received on the host channel. The next priority is the disk context so as to provide sufficient host channel activity to maintain continuous disk channel operation. The last priority is any other context corresponding to any other command which is neither an auto-write context or the present disk context.