User`s manual

siop_struc (Command Structure)

SBCSCSI/D1 B-11

CDB Length or Queue Depth

initiator mode

The CDB length field contains the length of the CDB, in bytes, that the user

wants to be transferred during the command phase. CDB lengths defined by

the SCSI specification are 6, 10, and 12 bytes.

config mode

TAG_Q bit set-

The user initializes this field with the maximum number of SCSI commands

the target LUN can queue at a time. A value up to 0xff means the initiator

mode Firmware dispatches up to that many commands to the target device

without waiting for SCSI status to be returned for any of the outstanding

commands. Any value over 0xff is not defined by the current SCSI

specification and a Firmware error is generated. The Firmware interprets a

value of zero (0) to mean untagged queuing and the Firmware control fields

are set to reflect non-support of tagged command queuing. Untagged queuing

is implicitly supported by the Firmware; therefore, a value of zero (0) should

only be used to disable tagged command queuing after it has been enabled.

CDB

initiator mode

The CDB field contains the CDB that is to be transferred during the command

phase on the SCSI bus for this command structure.

Message-In Length

This field may be modified by the Firmware.

initiator mode

The value in this field is used for buffer over-run control. The value in this

field is decremented as the returned message bytes are placed in the Message-

In buffer. If the MIBUF bit is not set then this value is initialized to 12 and the

Message-In Pointer field is initialized to point to the Message-In Bytes buffer

within this command structure. The Firmware receives all messages from the

target. The only messages placed in the buffer (returned to the user), however,

are SCSI extended messages.