Execution Of Target Mode Operations With A Prepared Ccb - Adaptec AHA-1740A Technical Reference Manual

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If a check condition status is received from the target, the AHA-1740A/1742A/1744
will issue a Request Sense command to get the sense data. The sense data is stored
in the CCB after the SCSI command data. The driver software must reserve the allo-
cated number of bytes at the end of the CCB to hold the sense data which is returned
as result of a receiving a check status. Automatic request sense can be optionally dis-
abled by jumpers or by using the CCB.
If the MBO command is to abort a SCSI command, the host adapter first searches
the active and queued CCBs. If the CCB is found, the task is aborted at the earliest
possible moment and an MBI entry is made to indicate that the CCBs execution was
successfully terminated. If the CCB is not found among the active or queued CCBs,
the AHA-1740A/1742A/1744 completes the command and reports that fact in the
MBI Status byte. The CCB may not be found because it has previously been aborted,
because an intervening reset occurred, or because the CCB was already finished nor-
mally and returned.
The AHA-1740A/1742A/1744 scans the MBOs in a round-robin fashion. This is to en-
sure that all of the mailboxes will be scanned with equal probability. A host can mini-
mize the AHA-1740A/1742A/1744 MBO scan time by using MBOs sequentially.
When executing a Start SCSI command, the AHA-1740A/1742A/1744 does not verify
that the new CCB resides in an unused memory area. Therefore, the host must not
reuse a CCB location until it has been returned through a Mailbox In entry and the
host has examined all the pertinent information in the CCB. CCB addresses are used
by the AHA-1740A/1742A/1744 as task identifiers.

Execution of Target Mode Operations With a Prepared CCB

Typical target operation is managed in the following way by the host software. After
power-on initialization is complete, the host sends an Enable Target Mode command
to the host adapter to enable processor Target Mode. After that, the host, from pre-
vious configuration knowledge, generates a pair of CCBs for each likely initiator and
for each LUN supported by the host. One CCB is for outbound data from the initiator
using the Send command, while the other is for inbound data from the target to the
initiator using the Receive command. The Send command CCB defines a data buffer
for the expected network-type command from the initiator. The Receive command
CCB defines a set of data which is known and expected by the initiator, typically a
welcome or configuration-type message packet. The host adapter tests to be sure that
duplicate CCBs are not provided by the host.
As the initiator finishes its initialization procedure, it requests availability and con-
figuration information using the Test Unit Ready, Request Sense, and Inquiry com-
mands. Finally, it may choose to address Send and Receive commands to the targets
it has located to transmit or request information packets.
When the initiator executes a Send or a Receive command, the target accepts the se-
lection on the SCSI bus, accepts the command from the initiator, and executes the
proper data transfer to or from the area specified by the proper CCB. When all SCSI
activity is finished successfully, the CCB is posted back to the host program by an en-
try in the MBI. The host adapter updates the CCB byte count and CDB field contents
to correctly reflect the operation performed. The host is notified that there is an entry
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AHA-1740A/1742A/1744