User Manual

SCSI Commands Reference Manual, Rev. J 195
www.seagate.com Direct Access Block commands (SPC-5 and SBC-4)
3.37 REQUEST SENSE command
The REQUEST SENSE command (see table 164) requests that the device server transfer sense data to the application client.
DESC (Descriptor Format) bit
The descriptor format (DESC) bit specifies which sense data format shall be returned.
0 If DESC is set to zero, fixed format sense data shall be returned (see 2.4.1.2).
1 If DESC is set to one and descriptor format sense data is supported, descriptor format sense data shall be returned (see 2.4.1.1).
ALLOCATION LENGTH field
The ALLOCATION LENGTH field is defined in 2.2.6. Application clients should request 252 bytes of sense data to ensure they retrieve all the
sense data. If fewer than 252 bytes are requested, sense data may be lost since the REQUEST SENSE command with any allocation length clears
the sense data.
Sense data shall be available and cleared under the conditions defined in SAM-5. If the device server has no other sense data
available to return, it shall:
1) return the sense key set to NO SENSE, additional sense code set to NO ADDITIONAL SENSE INFORMATION and;
2) complete the REQUEST SENSE command with GOOD status.
3) On completion of the command 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 power condition timers.
The device server shall return CHECK CONDITION status for a REQUEST SENSE command only to report exception conditions
specific to the REQUEST SENSE command itself.
Examples of conditions that cause a REQUEST SENSE command to return a CHECK CONDITION status are:
a) An invalid field value is detected in the CDB;
b) The device server does not support the REQUEST SENSE command (see 3.37);
c) An unrecovered error is detected by the service delivery subsystem; or
d) A malfunction prevents return of the sense data.
Device servers shall return at least 18 bytes of parameter data in response to a REQUEST SENSE command if the allocation length
is 18 or greater and the DESC bit is set to zero. Application clients may determine how much sense data has been returned by
examining the ALLOCATION LENGTH field in the CDB 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.
Table 164 REQUEST SENSE command
Bit
Byte
7 6 5 4 3 2 1 0
0
OPERATION CODE (03h)
1
Reserved DESC
2
Reserved
3
4
ALLOCATION LENGTH
5
CONTROL