Commands for all device types LOG SENSE command MODE SELECT(10) command
SCSI-2

8.2.8 MODE SELECT(6) command

The MODE SELECT(6) command (see table 52) provides a means for the initiator to specify medium, logical unit, or peripheral device parameters to the target. Targets that implement the MODE SELECT command shall also implement the MODE SENSE command. Initiators should issue MODE SENSE prior to each MODE SELECT to determine supported pages, page lengths, and other parameters.

Table 52 - MODE SELECT(6) command 

===============================================================================
|  Bit|   7    |   6    |   5    |   4    |   3    |   2    |   1    |   0    |
|Byte |        |        |        |        |        |        |        |        |
|=============================================================================|
| 0   |                           Operation code (15h)                        |
|-----------------------------------------------------------------------------|
| 1   | Logical unit number      |   PF   |         Reserved         |  SP    |
|-----------------------------------------------------------------------------|
| 2   |                           Reserved                                    |
|-----------------------------------------------------------------------------|
| 3   |                           Reserved                                    |
|-----------------------------------------------------------------------------|
| 4   |                           Parameter list length                       |
|-----------------------------------------------------------------------------|
| 5   |                           Control                                     |
===============================================================================
If a target supports saved pages, it may save only one copy of the page for each logical unit and have it apply to all initiators, or it may save separate copies for each initiator for each logical unit. If separate copies are saved, the target shall maintain separate current values for each I_T_L nexus. Pages that are common to all initiators are not required to have multiple copies.

If an initiator sends a MODE SELECT command that changes any parameters applying to other initiators, the target shall generate a unit attention condition for all initiators except the one that issued the MODE SELECT command (see 7.9). The target shall set the additional sense code to MODE PARAMETERS CHANGED.

The target may provide for independent sets of parameters for each attached logical unit or for each combination of logical unit and initiator. If independent sets of parameters are implemented, and a third party reservation is requested, the target transfers the set of parameters in effect for the initiator of the RESERVE command to the parameters used for commands from the third party device (see 9.2.12.3 and 10.2.10.1).

A page format (PF) bit of zero indicates that the MODE SELECT parameters are as specified in SCSI-1, (i.e. all parameters after the block descriptors are vendor-specific). A PF bit of one indicates that the MODE SELECT parameters following the header and block descriptor(s) are structured as pages of related parameters and are as specified in this standard.

A save pages (SP) bit of zero indicates the target shall perform the specified MODE SELECT operation, and shall not save any pages. An SP bit of one indicates that the target shall perform the specified MODE SELECT operation, and shall save to a non-volatile vendor-specific location all the savable pages including any sent during the DATA OUT phase. The SP bit is optional, even when mode pages are supported by the target. Pages that are saved are identified by the parameter savable bit that is returned in the page header by the MODE SENSE command (see 8.3.3). If the PS bit is set in the MODE SENSE data then the page shall be savable by issuing a MODE SELECT command with the SP bit set. If the target does not implement saved pages and the SP bit is set to one, the command shall be terminated with CHECK CONDITION status. The sense key shall be set to ILLEGAL REQUEST, and the additional sense code set to INVALID FIELD IN CDB.

The parameter list length field specifies the length in bytes of the mode parameter list that shall be transferred from the initiator to the target during the DATA OUT phase. A parameter list length of zero indicates that no data shall be transferred. This condition shall not be considered as an error.

The target shall terminate the command with CHECK CONDITION status if the parameter list length results in the truncation of any mode parameter header, mode parameter block descriptor(s), or mode page. The sense key shall be set to ILLEGAL REQUEST, and the additional sense code shall be set to PARAMETER LIST LENGTH ERROR.

The mode parameter list for the MODE SELECT and MODE SENSE commands is defined in 8.3.3. Parts of each mode parameter list are uniquely defined for each device-type.

The target shall terminate the MODE SELECT command with CHECK CONDITION status, set the sense key to ILLEGAL REQUEST, set the additional sense code to INVALID FIELD IN PARAMETER LIST, and shall not change any mode parameters for the following conditions:

  1. If the initiator sets any field that is reported as not changeable by the target to a value other than its current value.
  2. If the initiator sets any field in the mode parameter header or block descriptor(s) to an unsupported value.
  3. If an initiator sends a mode page with a page length not equal to the page length returned by the MODE SENSE command for that page.
  4. If the initiator sends a unsupported value for a mode parameter and rounding is not implemented for that mode parameter.
  5. If the initiator sets any reserved field in the mode parameter list to a non-zero value.

If the initiator sends a value for a mode parameter that is outside the range supported by the target and rounding is implemented for that mode parameter, the target may either:

  1. round the parameter to an acceptable value and terminate the command as described in 7.5.4;
  2. terminate the command with CHECK CONDITION status, the sense key set to ILLEGAL REQUEST, and set the additional sense code to INVALID FIELD IN PARAMETER LIST.

A target may alter any mode parameter in any mode page (even those reported as non-changeable) as a result of changes to other mode parameters.

The target validates the non-changeable mode parameters against the current values that existed for those mode parameters prior to the MODE SELECT command.

( If the current values calculated by the target affect the initiator's operation, the initiator should issue a MODE SENSE command after each MODE SELECT command. )