Mailbox In Definition - Adaptec AHA-1740A Technical Reference Manual

EISA-to-Fast SCSI Host Adapter
host adapter will not change the MBOA interrupt bit and will continue to scan
for other stored MBO entries.
3. If interrupts other than the Mailbox Out Available interrupt are pending, the host
adapter will wait for the pending interrupts to be cleared before setting the Mail-
box Out Available Interrupt. This guarantees that the MBO Available interrupt
will not be cleared accidentally by clearing another interrupt.

Mailbox In Definition

The Mailbox In entries are used to pass completion information concerning a task
from the host adapter to the host. In addition, requests for Target Mode CCBs are
passed to the host using MBI entries. The first byte of each MBI contains the MBI
Status byte, summarizing the type of information being passed from the host adapter
to the host. The remaining three bytes contain specialized information that provides
more detail about the information. In the case of a CCB Completed MBI, the bytes
contain a pointer to the completed CCB. In the case of a CCB Required MBI, the
bytes 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 host
adapter 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 adapter
scans the first byte of an MBI entry to find a free mailbox. If one is found, the host
adapter 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:
Standard Mode Firmware Description
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