in the MBI by an interrupt from the host adapter. The host then prepares a newCCB to control the target’s next activity expected from the initiator.Execution of Target Mode Operations Without a Prepared CCBAlternatively, the processor-type device may be addressed by an initiator when noCCB has yet been prepared for use by the host adapter. If the host adapter commandenabling target mode has not yet been executed, the host adapter will act like any in-itiator. It will not accept any selection sequence and any attempts to select it by itstarget ID will cause the initiator to detect a selection time out.If the host adapter has been enabled as a processor target by a host adapter com-mand, any selection to the host adapter’s target address will be accepted. The avail-ability commands and identification commands (Test Unit Ready, Request Sense,and Inquiry) will be executed completely and normally. If a Send or Receive com-mand is received and if a CCB is not active, either because the host has not com-pleted its program initialization or because the host has not finished analyzing theresults of previous data transfers and has not generated a new CCB, the processortarget will accept the selection, obtain the Identify Message Out to determine whatlogical unit has been selected, input the CDB from the SCSI, and then disconnect.The CDB will be partially interpreted so that the proper MBI can be generated to no-tify the host that a new CCB with a certain address, direction, and data length mustbe generated. When the new CCB is passed to the host adapter by an MBO entry, theCCB is filled up with the command information, the SCSI is reconnected, and thecommand is completed as described above.DMA Channel Initialization (with Host Adapter BIOS Disabled)The DMA circuitry must be set to a special state to allow the Bus Master operation ofthe AHA-1740A/1742A/1744 to operate correctly. This state is normally establishedby the BIOS during initialization so that no other activity is required. If a DMA chan-nel other than the default channel is being used or if the DMA channel is manipu-lated by other programs, the circuitry must be initialized in the following way beforethe AHA-1740A/1742A/1744 can be used.For the DMA channel being used, two bytes of data must be written to the DMA con-troller port specified to initialize the host DMA controller for Bus Master DMA opera-tion. The following table specifies these values in hex.EISA-to-Fast SCSI Host Adapter Standard Mode Firmware Description5-31
