host adapter will not change the MBOA interrupt bit and will continue to scanfor other stored MBO entries.3. If interrupts other than the Mailbox Out Available interrupt are pending, the hostadapter will wait for the pending interrupts to be cleared before setting the Mail-box Out Available Interrupt. This guarantees that the MBO Available interruptwill not be cleared accidentally by clearing another interrupt.Mailbox In DefinitionThe Mailbox In entries are used to pass completion information concerning a taskfrom the host adapter to the host. In addition, requests for Target Mode CCBs arepassed to the host using MBI entries. The first byte of each MBI contains the MBIStatus byte, summarizing the type of information being passed from the host adapterto the host. The remaining three bytes contain specialized information that providesmore detail about the information. In the case of a CCB Completed MBI, the bytescontain a pointer to the completed CCB. In the case of a CCB Required MBI, thebytes contain the information necessary for the host to prepare an appropriate CCB.Only those MBIs with an MBI status that is nonzero have information for the host.When the host returns the MBI status byte to zero, the MBI Free state, the hostadapter is allowed to place a new set of information in the MBI entry.When a SCSI command completes or if a new CCB is required, the host adapterscans the first byte of an MBI entry to find a free mailbox. If one is found, the hostadapter will update the MBI’s status byte with a nonzero value and update the follow-ing bytes with the appropriate required pointers or parameters. The valid MBI for-mats are defined below:EISA-to-Fast SCSI Host Adapter Standard Mode Firmware Description5-17
