Request Sense Command (03H) - Seagate Ultra160 Product Manual

SCSI Interface Product Manual, Rev. B
8.38

REQUEST SENSE command (03h)

The REQUEST SENSE command (Table 218) requests that the device server transfer sense data to the appli-
cation client in the format shown in Table 219.
If any nonfatal error occurs during execution of REQUEST SENSE, the drive shall return sense data with
GOOD status. Following a fatal error on a REQUEST SENSE command, sense data may be invalid.
Table 218: REQUEST SENSE command (03h)
7
Bit
Byte
0 OPERATION CODE (03h)
1 Reserved
Reserved
2 Reserved
3 Reserved
4 ALLOCATION LENGTH [1]
5 CONTROL [2]
[1] The ALLOCATION LENGTH in byte four of the format shown specifies the number of bytes the initiator
has allocated for returned sense data. The ALLOCATION LENGTH should always be at least 18 bytes for
drive devices for the initiator to receive all of the drive sense data. Any other value indicates the maximum
number of bytes that shall be transferred. The drive shall terminate the DATA IN phase when ALLOCA-
TION LENGTH bytes have been transferred or when all available sense data have been transferred to the
initiator, whichever is less. The drive always returns sense data in the Extended Sense Data Format.
[2] See Table 61, "CONTROL field," in Section 7.2.1.
Sense data shall be available and cleared under the conditions defined in SAM-2. If the device server has no
other sense data available to return, it shall return a sense key of No Sense and an additional sense code of
No Additional Sense Information.
If the device server is in the STANDBY POWER condition or IDLE POWER condition when a REQUEST
SENSE command is received and there is no ACA or CA condition, the device server shall return a sense key
of NO SENSE and an additional sense code of LOW POWER CONDITION ON. On completion of the com-
mand the logical unit shall return to the same power condition that was active before the REQUEST SENSE
command was received. A REQUEST SENSE command shall not reset any active power condition timers.
The device server shall return CHECK CONDITION status for a REQUEST SENSE command only to report
exception conditions specific to the command itself. For example:
a. An invalid field value is detected in the command descriptor block;
b. An unrecovered parity error is detected by the service delivery subsystem; or
c. a SCSI target port malfunction that prevents return of the sense data.
If a recovered error occurs during the execution of the REQUEST SENSE command, the device server shall
return the sense data with GOOD status. If a device server returns CHECK CONDITION status for a
REQUEST SENSE command, the sense data may be invalid.
Note. The sense data appropriate to the selection of an invalid logical unit is defined in SAM-2.
Device servers shall be capable of returning eighteen bytes of data in response to a REQUEST SENSE com-
mand. If the ALLOCATION LENGTH is 18 or greater, and a device server returns less than 18 bytes of data,
the application client should assume that the bytes not transferred would have been zeros had the device
server returned those bytes. Application clients may determine how much sense data has been returned by
examining the ALLOCATION LENGTH field in the command descriptor block and the Additional Sense Length
field in the sense data. Device servers shall not adjust the additional sense length to reflect truncation if the
ALLOCATION LENGTH is less than the sense data available.
6 5 4 3 2 1
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