SCSI Primary Commands - 2.pdf

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T10/1236-D Revision 20 18 July 2001A six-byte CDB contains a 21-bit LOGICAL BLOCK ADDRESS field. The ten-byte and the twelve-byte CDBs contain32-bit LOGICAL BLOCK ADDRESS fields. The sixteen-byte CDB has two formats one with a 32-bit LOGICAL BLOCKADDRESS field (see table 4) and one with a 64-bit LOGICAL BLOCK ADDRESS field (see table 5). LOGICAL BLOCKADDRESS fields in additional parameter data have their length specified for each occurrence. See the specificcommand descriptions.4.3.4.4 Transfer lengthThe TRANSFER LENGTH field specifies the amount of data to be transferred, usually the number of blocks. Somecommands use transfer length to specify the requested number of bytes to be sent as defined in the commanddescription. See the following descriptions and the individual command descriptions for further information.Commands that use one byte for the TRANSFER LENGTH field allow up to 256 blocks of data to be transferred by onecommand. A TRANSFER LENGTH value of 1 to 255 indicates the number of blocks that shall be transferred. A valueof zero specifies that 256 blocks shall be transferred.In commands that use multiple bytes for the TRANSFER LENGTH field, a transfer length of zero indicates that no datatransfer shall take place. A value of one or greater indicates the number of blocks that shall be transferred.Refer to the specific command description for further information.4.3.4.5 Parameter list lengthThe PARAMETER LIST LENGTH field is used to specify the number of bytes sent from the Data-Out Buffer. This field istypically used in CDBs for parameters that are sent to a device server (e.g., mode parameters, diagnostic parameters,log parameters). A parameter length of zero indicates that no data shall be transferred. This condition shallnot be considered as an error.4.3.4.6 Allocation lengthThe ALLOCATION LENGTH field specifies the maximum number of bytes that an application client has allocated forreturned data. An allocation length of zero indicates that no data shall be transferred. This condition shall not beconsidered as an error. The device server shall terminate transfers to the Data-In Buffer when allocation lengthbytes have been transferred or when all available data have been transferred, whichever is less. The allocationlength is used to limit the maximum amount of data (e.g., sense data, mode data, log data, diagnostic data)returned to an application client. If the information being transferred to the Data-In Buffer includes fields containingcounts of the number of bytes in some or all of the data, the contents of these fields shall not be altered to reflectthe truncation, if any, that results from an insufficient ALLOCATION LENGTH value, unless the standard that describesthe Data-In Buffer format specifically states otherwise.If the amount of information to be transferred exceeds the maximum value that may be specified in the ALLOCATIONLENGTH field the device server shall transfer no data and return a CHECK CONDITION status; the sense key shallbe set to ILLEGAL REQUEST and the additional sense code shall be set to INVALID FIELD IN CDB.4.3.4.7 ControlThe contents of the CONTROL field are defined in SAM-2. The CONTROL field has a consistently defined meaningacross all commands.18 dpANS SCSI Primary Commands - 2 (SPC-2)
18 July 2001 T10/1236-D Revision 205 Model common to all device types5.1 Introduction to the model common to all device typesThis model describes some of the general characteristics expected of most SCSI devices. It is not intended to alterany requirements defined elsewhere in SCSI. Devices conforming to this standard also shall conform to SAM-2.5.2 Commands implemented by all SCSI device servers5.2.1 Summary of commands implemented by all SCSI device serversThis standard defines three commands that all SCSI device servers shall implement - INQUIRY, REQUESTSENSE, and TEST UNIT READY. These commands are used to configure the system, to test devices, and toreturn important information concerning errors and exception conditions.5.2.2 Using the INQUIRY commandThe INQUIRY command may be used by an application client to determine the configuration of the logical unit.Device servers respond with information that includes their type and standard version and may include the vendor'sidentification, model number and other information. It is recommended that device servers be capable of returningthis information (or whatever part of it that is available) upon completing power-on initialization. A device servermay take longer to get certain portions of this information, especially if it retrieves the information from the medium.5.2.3 Using the REQUEST SENSE commandWhenever a command completes with a CHECK CONDITION status and autosense data is not provided, the applicationclient that received the error status should issue a REQUEST SENSE command to receive the sense datadescribing the cause of the condition. If the application client issues a command other than REQUEST SENSE,the sense data is lost.5.2.4 Using the TEST UNIT READY commandThe TEST UNIT READY command allows an application client to poll a logical unit until it is ready without the needto allocate space for returned data. The TEST UNIT READY command may be used to check the media status oflogical units with removable media. Device servers should respond promptly to indicate the current status of theSCSI device, delays to achieve GOOD status may adversely affect initiator performance.5.3 Parameter roundingCertain parameters sent to a device server with various commands contain a range of values. Device servers maychoose to implement only selected values from this range. When the device server receives a value that it doesnot support, it either rejects the command (CHECK CONDITION status with ILLEGAL REQUEST sense key) or itrounds the value received to a supported value.When parameter rounding is implemented, a device server that receives a parameter value that is not an exactsupported value shall adjust the value to one that it supports and shall return CHECK CONDITION status with asense key of RECOVERED ERROR. The additional sense code shall be set to ROUNDED PARAMETER. Theapplication client should issue an appropriate command to learn what value the device server has selected.dpANS SCSI Primary Commands - 2 (SPC-2) 19
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