Method for accessing a sequencer control block by a host adapter

Details Method for accessing a sequencer control block by a host adapter Method for accessing a sequencer control block by a host adapter

1994-06-30

1996-10-08

Harvey, Jack B.

395412, 395417, 395419, G06F 1300

Patent

active

055640230

ABSTRACT:
A busy targets table is created in a memory that can be either internal or external to a SCSI host adapter. Each entry in the table initially is set to a predetermined value. Prior to starting execution of each hardware request block, the host adapter performs a check to determine whether the hardware request block can be executed at this time by generating an offset into the busy targets table using a target address in the hardware request block. The host adapter then checks the entry in the busy targets table at the location of the offset. If the entry in the busy targets table at the location of the offset is the predetermined value, the device at the target address, i.e., the target, is available. Therefore, the execution of the hardware request block can proceed and so the host adapter overwrites the predetermined value at the offset in the table with a pointer to a storage location of said SCSI hardware request block and continues executing the hardware request block. If the target disconnects from the host adapter, the busy targets table is used to locate the appropriate hardware request block when the target reconnects to the host adapter. Specifically, the host adapter generates an offset into the busy targets table using target address information provided by the target. The host adapter uses the offset to locate the pointer stored in the busy targets table and then locates the appropriate hardware request block using the pointer.

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