User's Guide

Chapter 3 Emulated DLT7000 SCSI Commands
Overview of Command and Status Processing
Quantum DX-Series Software Interface Guide 113
Table 74 Command
Descriptor Block
Control Field - Field
Descriptions
Status/Error
Reporting
3
SCSI message-level errors are communicated by messages that are
defined specifically for that purpose (for example, MESSAGE PARITY
ERROR, MESSAGE REJECT). Message-level errors are also handled by
drive-managed retries. Refer to Chapter 4 for more detailed message-
handling information.
SCSI command-level errors are communicated by a status code that is
returned by the drive during the STATUS phase. This phase occurs at the
end of each command, unless the command is terminated by one of the
following events:
•ABORT message
• BUS DEVICE RESET message
• Hard reset condition
Field Description
Vendor Specific Bits These bits must be 0.
Flag Bit The Flag bit is used in conjunction with the Link bit to notify the
initiator in an expedient manner that a command has been completed.
Tech Tip: Flag bits are not supported by the DX-Series system.
Link Bit A Link bit set to 1 indicates that the initiator requests continuation of a
task (an I/O process) across two or more SCSI commands.
If the Link bit is 1 and the Flag bit is 0, and the task completes
successfully, the drive continues the task and returns a status of
INTERMEDIATE and a LINKED COMMAND COMPLETE message.
If the Link bit and the Flag bit within a Control word are both set to 1,
and the drive completes a command with a status of INTERMEDIATE,
the drive returns a LINKED COMMAND COMPLETE message (with
Flag).
Tech Tip: Link bits are not supported by the DX-Series system.