SCSI Primary Commands - 2.pdf

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T10/1236-D Revision 20 18 July 2001When the processor device is a source, the number of bytes to be transferred by a SEND command shall bespecified by STREAM DEVICE TRANSFER LENGTH field in the segment descriptor. When the processor device is adestination, the number of bytes to be transferred by a RECEIVE command shall be specified by STREAM DEVICETRANSFER LENGTH field in the segment descriptor.7.2.7 Segment Descriptors7.2.7.1 Segment descriptors introductionAll segment descriptors begin with the eight byte header shown in table 28.Table 28 — Segment descriptor headerBitByte7 6 5 4 3 2 1 00 DESCRIPTOR TYPE CODE (00h-3Fh)1 Reserved DC CAT2 (MSB)DESCRIPTOR LENGTH3 (LSB)4 (MSB)SOURCE TARGET DESCRIPTOR INDEX5 (LSB)6 (MSB)DESTINATION TARGET DESCRIPTOR INDEX7 (LSB)The descriptor type code field is described in 7.2.5. Support for each segment descriptor format is optional. Ifcopy manager receives an unsupported descriptor type code in a segment descriptor, the command shall be terminatedwith CHECK CONDITION status. The sense key shall be set to ILLEGAL REQUEST and the additionalsense code shall be set to UNSUPPORTED SEGMENT DESCRIPTOR TYPE CODE.The destination count (DC) bit is only applicable to segment descriptors with descriptor type code values of 02h and0Dh. The DC bit is reserved for all other segment descriptors. Details of usage for the DC bit appear in thesubclauses defining the segment descriptors that use it.The CAT bit is described in 7.2.7.2.The DESCRIPTOR LENGTH field contains the length in bytes of the fields that follow the DESCRIPTOR LENGTH field in thesegment descriptor. In most cases, the length is constant.The SOURCE TARGET DESCRIPTOR INDEX field contains an index into the target descriptor list (see 7.2.1) identifyingthe source target device. The DESTINATION TARGET DESCRIPTOR INDEX field contains an index into the targetdescriptor list (see 7.2.1) identifying the destination target device. Some segment descriptor formats do not requirea SOURCE TARGET DESCRIPTOR INDEX field or a DESTINATION TARGET DESCRIPTOR INDEX field, in which case the fieldis reserved.If the target identified by a SOURCE TARGET DESCRIPTOR INDEX field or a DESTINATION TARGET DESCRIPTOR INDEX fieldis not accessible to the copy manager, then the command shall be terminated with a CHECK CONDITION status,the sense key shall be set to COPY ABORTED and the additional sense code shall be set to UNREACHABLECOPY TARGET.58 dpANS SCSI Primary Commands - 2 (SPC-2)
18 July 2001 T10/1236-D Revision 207.2.7.2 Segment descriptor processingIn processing a segment descriptor, the copy manager may be required:a) To read source data by issuing data input commands to the source device;b) To process data, an operation that generally designates data as destination data intended for transfer tothe destination device; andc) To write some or all of the destination data to the destination device.The number of blocks to read and write, the number of bytes to process, and the nature of processing are determinedby the segment descriptor type code, the parameters of the segment descriptor, and the amount of residualsource or destination data retained from the previous segment, if any.Except as otherwise specified by particular segment descriptor type codes:a) Just enough whole-block read operations shall be performed to supply, together with residual source datafrom the previous segment or segments, the number of bytes to be processed;b) Processing consists of removing bytes from the source data and designating them as destination data,without change.c) As many whole-block write operations as possible shall be performed with the destination data, includingany residual destination data from the previous segment or segments.Any residual source data from the previous segment or segments shall be processed before any data read from thesource device during processing of the current segment descriptor. Any residual destination data from the previoussegment or segments shall be written before any data processed during processing of the current segmentdescriptor.Exceptions and clarifications to these general rules are described in table 29 and the subclauses it references.Table 29 — Descriptor Type Code Dependent Copy Manager Processing (part 1 of 2)Segment Descriptor Type Code Reference Description00h (block→stream) or0Bh (block→stream+application client)02h (block→block) or0Dh (block→block+application client)with DC=002h (block→block) or0Dh (block→block+application client)with DC=101h (stream→block) or0Ch (stream→block+application client)09h (stream→block) 7.2.7.1203h (stream→stream) or0Eh (stream→stream+application client)a7.2.7.3 The number of bytes processed is determined by theBLOCK DEVICE NUMBER OF BLOCKS field for the sourceblocks (see applicable type code definition subclauses7.2.7.5for details). a7.2.7.5 The number of blocks or byte range specified shall beoutput to the destination device. If residual destinationdata is sufficient to perform the output then no datashall be processed. Otherwise, just as much data as7.2.7.3 needed shall be processed (which may involve readingdata from the source device) so that the destinationdata (which includes any residual destination data fromthe previous segment) is sufficient. a7.2.7.6 The number of bytes specified in the segmentdescriptor shall be processed. aFor segment descriptor type codes 0Bh, 0Ch, 0Dh and 0Eh, a copy of the processed data shall also be heldfor retrieval by the application client.dpANS SCSI Primary Commands - 2 (SPC-2) 59
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