Control Block is Queued for OperationA control block is queued for operation when it has not yet initiated any activity onthe SCSI bus. The host adapter will terminate the control block and place it on the in-terrupt queue. When the host is interrupted for this control block, the EnhancedMode (Group 2) Interrupt Status register will report control block complete with er-ror. The Mailbox In registers will contain the address of the aborted control block.The status block will report a major error/exception and the host adapter status willindicate that the control block was aborted by the host. If chaining was enabled forthis control block, the chain will be halted.Associated Target for the Control Block is DisconnectedIf the command had been initiated, but the target had disconnected, the host adapterwill terminate the control block as described above. When the target reconnects, thehost adapter will issue an Abort (or Abort Tag) message.NoteEven though the control block will be terminated and reported back to the host, thehost adapter must maintain a history of the control block in its internal RAM in or-der to send the Abort message when the target reconnects. It is possible that thetarget may never reconnect. If this happens, the host adapter will continue to oper-ate normally, but that portion of internal RAM will be lost as a resource until aDevice Reset or Host Adapter Reset is issued.Control Block is Currently Active on the SCSI BusIf the command had been initiated and the target was currently active on the SCSIbus, the host adapter will assert the Attention signal. If the target responds to Atten-tion with Message Out phase, the host adapter will issue an Abort (or Abort Tag)message which forces the target to go bus free. If the target goes bus free either fromthe Abort message, disconnection, or command completion, the host adapter will ter-minate the control block as described above.If the target does not go bus free within 250 milliseconds, the host adapter will resetthe SCSI bus to force the target off the bus. The control block will be terminated asdescribed above except that the host adapter status byte in the status block of thecontrol block will reflect that the target did not respond to Attention.Control Block in the Interrupt QueueIf the command had already been completed and an interrupt was pending to thehost for the associated control block, the host adapter will report the completion ofthe control block normally. The abort operation will have no affect.NoteThere is no interrupt associated with the abort operation. Its sole purpose is to pre-maturely terminate any control block queued or in progress.adaptec AHA-1740A/1742A/17446-40
