SCSI Primary Commands - 2.pdf

T10/1236-D Revision 20 18 July 2001Table 82 — READ BUFFER descriptorBitByte7 6 5 4 3 2 1 00 OFFSET BOUNDARY13The OFFSET BOUNDARY field returns the boundary alignment within the selected buffer for subsequent WRITEBUFFER and READ BUFFER commands. The value contained in the OFFSET BOUNDARY field shall be interpretedas a power of two.The value contained in the BUFFER OFFSET field of subsequent WRITE BUFFER and READ BUFFER commandsshould be a multiple of 2 offset boundary as shown in table 83.The BUFFER CAPACITY field shall return the size of the selected buffer in bytes.NOTE 22 In a system employing multiple application clients, a buffer may be altered between the WRITE BUFFERand READ BUFFER commands by another application client. Buffer testing applications should insure that only asingle application client is active. Use of reservations to all logical units on the device or linked commands may behelpful in avoiding buffer alteration between these two commands.7.13.6 Read Data from echo buffer (1010b)BUFFER CAPACITYTable 83 — Buffer offset boundaryOffset boundary 2 Offset boundary Buffer offsets0h 2 0 = 1 Byte boundaries1h 2 1 = 2 Even-byte boundaries2h 2 2 = 4 Four-byte boundaries3h 2 3 = 8 Eight-byte boundaries4h 2 4 = 16 16-byte boundaries. . .FFh Not applicable 0 is the only supported buffer offsetIn this mode the device server transfers data to the application client from the echo buffer. The echo buffer shalltransfer the same data as when the WRITE BUFFER command with the mode field set to echo buffer was issued.The BUFFER ID and BUFFER OFFSET fields are ignored in this mode.The READ BUFFER command shall return up to the number of bytes of data as received in the prior echo buffermode WRITE BUFFER command from the same initiator. If the allocation length is insufficient to accommodatethe number of bytes of data as received in the prior echo buffer mode WRITE BUFFER command, the datareturned shall be truncated as described in 4.3.4.6, and this shall not be considered an error. If a prior echo buffermode WRITE BUFFER command was not successfully completed the echo buffer mode READ BUFFERcommand shall terminate with a CHECK CONDITION status, the sense key shall be set to ILLEGAL REQUESTand the additional sense code to COMMAND SEQUENCE ERROR. If the data in the echo buffer has beenoverwritten by another initiator the target shall terminate the echo buffer mode READ BUFFER command with aCHECK CONDITION status, the sense key shall be set to ABORTED COMMAND and the additional sense code toECHO BUFFER OVERWRITTEN.116 dpANS SCSI Primary Commands - 2 (SPC-2)