Digital Equipment Corporation

Compaq Computer Corporation, Inc.

Charles Monia

William Edward Ham

Fee Lee

A SCSI bus extender apparatus coupling a main SCSI bus to a auxiliary SCSI bus includes a mechanism for detecting and processing SELECTION and RESELECTION signals transmitted between the two buses to accommodate target devices on the auxiliary bus which support tagged queuing in accordance with the SCSI protocol. The invention contemplates reserving an address on the auxiliary bus for each initiator on the main bus and performing the appropriate address conversions to enable target devices to properly identify the correct initiator device during a RESELECTION phase.

SCSI bus extender utilizing tagged queuing in a multi-initiator environment

A SCSI bus extender apparatus coupling a primary SCSI bus to a secondary SCSI bus includes a mechanism for detecting and resolving contention between a substantially simultaneous SELECTION operation on the primary bus and a RESELECTION operation on the secondary bus. The inventive method contemplates the bus extender arbitrating for control of the primary bus after a conflict is detected, and releasing control of the secondary bus if control of the primary bus is obtained. A target device on the secondary bus can then rearbitrate for control of the secondary bus. Once the target device controls the secondary bus, it can direct a RESELECTION signal to the bus extender, which responsively directs the signal to an initiator device on the primary bus. If the bus extender is unable to gain control of the primary bus after a conflict is detected, the SELECTION operation is allowed to proceed and the target device reattempts to assert the RESELECTION operation thereafter.

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Marlboro, MA, United States of America

Charles Monia