5.3Status/Error Reporting

SCSI message-level errors are communicated by messages that are defined specifically for that purpose. SCSI command-level errors are communicated by a status 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 TASK SET message

•ABORT TASK message

•TARGET RESET message

•CLEAR QUEUE message

•Unexpected disconnect

The status code is contained in bits 1 through 5 of the status byte. Bits 0, 6, and 7 are reserved. Table 5-6describes the status codes returned by the drive.

 

 

Table 5-6Status Codes

 

 

 

 

Status

Definition

 

Meaning

 

 

 

 

00h

GOOD

 

The drive successfully completed the command.

 

 

 

 

02h

CHECK CONDITION

 

An Auto Contingent Allegiance (ACA) condition occurred.

 

 

 

 

 

 

 

The drive cannot service the command at the moment, and its Com-

 

 

 

mand Descriptor Block has been discarded. The initiator can retry the

 

 

 

command at a later time. This status is returned when:

 

 

 

• A non-tagged command is received and the logical unit's com-

 

 

 

mand queue is full (all internal command buffers are in use).

08h

BUSY

 

• A disconnect privilege was not granted in the IDENTIFY mes-

 

sage of a queue-tagged I/O process (Parallel SCSI).

 

 

 

 

 

 

• A disconnect privilege was not granted in the IDENTIFY mes-

 

 

 

sage of a non-tagged I/O process and a command from another

 

 

 

initiator is currently active (Parallel SCSI)

 

 

 

• A command is received while an auto-contingent allegiance

 

 

 

condition exists for another initiator.

 

 

 

 

 

 

 

This status is returned for every command (except the last) in a series

 

 

 

of linked commands that was successfully completed. However, if the

10h

INTERMEDIATE

 

command is terminated with other that GOOD status (such as

 

CHECK CONDITION, RESERVATION CONFLICT, OR

 

 

 

 

 

 

BUSY), the INTERMEDIATE status is not returned and the series of

 

 

 

linked commands and the task is ended.

 

 

 

 

18h

RESERVATION CONFLICT

Another initiator has reserved the drive. (This status is never returned

for INQUIRY or REQUEST SENSE commands.)

 

 

 

 

 

 

 

 

 

 

The drive cannot service the command at the moment, and its Com-

 

 

 

mand Descriptor Block has been discarded. (Returned for a tagged

28h

TASK SET FULL

 

command when all of the drive's internal command buffers are in use,

 

 

 

or when a host sends a tagged command while an Auto Contingent

 

 

 

Allegiance condition is pending for that initiator)

 

 

 

 

5.4Linked Commands

An I/O Process (task) may contain multiple commands that are linked together. The initiator communicates this condition of linked (or unlinked) commands by setting (or clearing) the Link bit of the Command Descriptor Block’s control word. A linked

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