Control Block Is Queued For Operation; Associated Target For The Control Block Is Disconnected; Control Block Is Currently Active On The Scsi Bus; Control Block In The Interrupt Queue - Adaptec AHA-1740A Technical Reference Manual

adaptec

Control Block is Queued for Operation

A control block is queued for operation when it has not yet initiated any activity on
the 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 Enhanced
Mode (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 will
indicate that the control block was aborted by the host. If chaining was enabled for
this control block, the chain will be halted.

Associated Target for the Control Block is Disconnected

If the command had been initiated, but the target had disconnected, the host adapter
will terminate the control block as described above. When the target reconnects, the
host adapter will issue an Abort (or Abort Tag) message.
Even though the control block will be terminated and reported back to the host, the
host 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 the
target 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 a
Device Reset or Host Adapter Reset is issued.

Control Block is Currently Active on the SCSI Bus

If the command had been initiated and the target was currently active on the SCSI
bus, 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 from
the 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 reset
the SCSI bus to force the target off the bus. The control block will be terminated as
described above except that the host adapter status byte in the status block of the
control block will reflect that the target did not respond to Attention.

Control Block in the Interrupt Queue

If the command had already been completed and an interrupt was pending to the
host for the associated control block, the host adapter will report the completion of
the control block normally. The abort operation will have no affect.
There is no interrupt associated with the abort operation. Its sole purpose is to pre-
maturely terminate any control block queued or in progress.
6-40
Note
Note
AHA-1740A/1742A/1744