Fibre channel controller having both inbound and outbound control units for simultaneously processing both multiple inbound and outbound sequences

DETAILED DESCRIPTION The present invention pertains to a FC controller that interfaces between a host system and a 10-bit FC interface.
The FC controller has the capacity to act as both a fibre channel protocol (FCP) initiator and a FCP target device.
As a FCP initiator, the FC controller initiates SCSI I/O requests to a number of devices at the request of a host system.
As a FCP target, the FC controller receives SCSI I/O requests from devices linked through the FC.
The FC controller can process both an inbound and outbound sequence simultaneously since it does not employ a processor-based architecture.
Rather the FC controller relies on specialized circuitry that operates in a relatively independent manner so that multiple tasks are performed simultaneously thereby achieving a faster throughput and a higher data transfer rate.
A SCSI I/O request can be viewed as a FCP exchange having one or more sequences.
A FCP exchange can consist of any number of inbound and/or outbound sequences.
An outbound sequence transmits a command, data, and/or response phase to an initiator or target device and an inbound sequence receives a command, data, and/or response phase from an initiator or target device.
A sequence can be composed of one or more frames which is the basic data unit in the FC protocol.
The host system and the FC controller communicate through an interface that includes a number of data structures and a protocol specifying how the data structures are interpreted.
The data structures can include an exchange request queue (ERQ) that is used by the host system to initiate SCSI I/O requests, and a SCSI exchange state table (SEST).
A SEST entry includes the information needed to process a SCSI I/O request and which indicates where to retrieve or store the incoming data and/or response.
In addition, status information, in the form of a completion message, is posted in an inbound message queue (IMQ).
An initiator can send the target host system a SCSI I/O request which is received by the FC controller and stored in a single frame queue (SFQ)