User`s manual

SIOP Firmware Structures
B-6 Single Board Computers SCSI Software UserÕs Manual
B
Bit 15 -- MIBUF
initiator mode
If set, defines the message-in buffer pointer field to contain a pointer to a buffer
where messages from the target are to be saved. If clear, the messages are
saved in the 12-byte message-in field and the message-in buffer pointer field
is initialized by the Firmware. It is recommended to NOT set the MIBUF in the
command control field for normal operation; this feature of the Firmware is
intended to be used for very long extended messages.
Bit 14 -- MOBUF
initiator mode
If set, defines the message-out buffer pointer field to contain a pointer to a user
initialized buffer where messages to the target are located. The user also must
initialize the message-out length field to the byte count of the message
transfer. The user is responsible for ALL messages to be sent to the target. The
first byte in the buffer must be an identify message. The external message
buffer cannot contain synchronous data transfer request or wide data transfer
request messages. Synchronous data transfer negotiations and wide data
transfer negotiations must be handled by the Firmware. Additionally, if
tagged command queuing is enabled then this bit should not be set because if
the target disconnects and then reselects, the Firmware has no way of
rethreading for this nexus. If clear, the Firmware initializes the message-out
buffer pointer field and the message-out length field. Also the Firmware
generates all necessary message bytes such as identify (if the NO_ATN bit is
cleared), queue tag (if tagged queuing has been enabled in the Firmware),
synchronous data transfer request (if the SYNC or ASYNC bit is set), and wide data
transfer request (if the WIDE16 bit is set). It is recommended to NOT set the
MOBUF in the command control field for normal operation; this feature of the
Firmware is intended to be used for very long extended messages.
Bit 13 -- NO_ATN
initiator mode
If set, Firmware selects the target device without ATN asserted. This bit is set
if the user does not wish for the target device to disconnect during this
command. This bit cannot be used with SCSI linked commands or with
devices that have tagged command queuing enabled. For SCSI bus efficiency,
it is recommended to NOT set this bit.