Seagate Ultra 320, Ultra 160 Timing examples, Auto Contingent Allegiance or Contingent Allegiance

7.5Timing examples

Times (T00 through T35) necessary to define performance are listed in the individual drive’s Product Manual, in the “Disc drive SCSI timing” section. For timing waveforms to define these times, refer to the SCSI Parallel Interface-5 specification (SPI-5).

7.6Command processing considerations and exception conditions

The following clauses describe some exception conditions and errors associated with command processing and the sequencing of commands.

7.6.1Auto Contingent Allegiance or Contingent Allegiance

The auto contingent allegiance (NACA=1, see Section 7.2.1, note [7], Table 62) or contingent allegiance (NACA=0) condition shall exist within the task set when the logical unit completes a command by returning a CHECK CONDITION status (see Section 7.3).

7.6.1.1Logical Unit response to Auto Contingent Allegiance or Contingent Allegiance

The auto contingent allegiance (NACA=1, see Section 7.2.1, note [7], Table 62) or contingent allegiance (NACA=0) condition shall not cross task set boundaries and shall be preserved until it is cleared as described in Section 7.6.1.2. If requested by the application client and supported by the protocol and logical unit, sense data shall be returned as described in Section 7.6.4.2.

Note. The SCSI-2 contingent allegiance condition has had an alternate added and the extended contingent allegiance condition has been replaced in SCSI-3 (now called merely “SCSI”) by auto contingent alle- giance in conjunction with the NACA bit.

Note. If the SCSI-3 protocol does not enforce synchronization of client/server states, there may be a time delay between the occurrence of the auto contingent allegiance or contingent allegiance condition and the time at which the initiator becomes aware of the condition.

After sending status and a service response of Task Complete, the logical unit shall modify the state of all tasks in the faulted task set as described in SCSI Architecture Model-4 (SAM-4), T10/1683-D, “Task Set Manage- ment.”

A task created by the faulted initiator while the auto contingent allegiance condition is in effect may be entered into the faulted task set under the conditions described below.

As described in Section 7.2.1, note [7], Table 62, the setting of the NACA bit in the Control byte of the faulting command CDB determines the rules that apply to an ACA or CA condition caused by that command. If the NACA bit was set to zero the SCSI-2 contingent allegiance rules shall apply.

If the NACA bit was set to one in the Control byte of the faulting command, then a new task created by the faulted initiator while the ACA condition is in effect shall not be entered into the faulted task set unless all of the following conditions are true:

a.The task has the ACA attribute; and

b.No other task from the faulted initiator having the ACA attribute is in the task set.

If the task is from the faulted initiator and any of the conditions listed above are not met, the newly created task shall not be entered into the task set and shall be completed with a status of ACA Active.

If a task having the ACA attribute is received and no auto contingent allegiance condition is in effect for the task set or if the NACA bit was set to zero in the CDB for the faulting command (i.e., a contingent allegiance condi- tion is in effect), then the ACA task shall be completed with a status of Check Condition. The sense key shall be set to ILLEGAL REQUEST with an additional sense code of Invalid Message Error. As noted in Section 7.2.1, note [7], Table 62, any existing contingent allegiance condition shall be cleared and a new auto contin- gent allegiance (NACA=1) or contingent allegiance (NACA=0) condition shall be established.

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