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(3)
Command Completion Wait Time-out
This error is a state where the completed status for a command is not reported within the time
expected by the INIT that issued the command.
One cause of this error occurring, besides a malfunction of the IDD, is that the command was
cleared by some method which the INIT that issued the command cannot clearly detect, such
as a BUS DEVICE RESET message, or the command was cleared when an unrecoverable
error was detected in reconnection processing executed by the IDD, etc. When this error
occurs, the INIT should gather sense data by issuing the REQUEST SENSE command, then
judge which recovery method to use based on the contents of the sense data (see item 4.2.2).
Not only does command execution time differ widely depending on the type and specified
contents of the command, but since it has an influence on the following factors, it is necessary
to give adequate consideration to these points when setting the monitoring time value at the
INIT.
•
Since the command stack feature exists (see Section 1.4), even if the IDD accepts a
command normally, if a command issued by another INIT is being executed, or if there are
other commands in the stack, execution of the command is caused to wait until all the
other commands have been processed. The execution wait time is dependent upon the
type of command issued by the other INITs and the contents of its specifications.
•
If the IDD has executed error recovery processing (retried) for an error that occurred on the
SCSI bus or in the disk drive, command completion time will be longer than normal.
(4)
BUS FREE Error
This error occurs in the case that the SCSI bus enters the BUS FREE phase at a time when the
INIT is not expecting it, during execution of a command on the SCSI bus. Even in cases
where a RESET condition is generated by another SCSI device on the bus, the same state
occurs, but the occurrence of an unexpected RESET condition should be processed as an
abnormal state of the system.
The cause of this error is the occurrence of an unrecoverable error on the SCSI bus, the
occurrence of a serious protocol error, etc. For details concerning the causes of errors, see
Chapter 3, "SCSI Bus Error Recovery Processing" in Chapter 3 of the "OEM Manual Interface
Specifications." When this error is detected, the INIT should issue the REQUEST SENSE
command and gather sense data then judge the error recovery method according to the
contents of the sense data (see item 4.2.2).
4.2.2
Sense Data Analysis and Error Recovery Methods
The INIT can judge the procedure for error recovery by analyzing the contents of the sense
data fetched by the REQUEST SENSE command. Table 4.3 the classifications of error
information displayed in the sense data are shown and in Table 4.4, the procedures for error
recovery recommended for the INIT to execute are shown. The error recovery procedure
which can be executed by the INIT will differ depending on the system's condition, so the
optimum processing procedure should be selected for the user system with reference to the
following descriptions.
