SCSI Primary Commands - 2.pdf

18 July 2001 T10/1236-D Revision 20The initiator may send a READ BUFFER command requesting the echo buffer descriptor prior to a WRITEBUFFER command.If an echo buffer mode WRITE BUFFER command is successful then the initiator may send multiple echo buffermode READ BUFFER commands to read the echo buffer data multiple times.7.13.7 Echo buffer descriptor mode (1011b)In this mode, a maximum of four bytes of READ BUFFER descriptor information is returned. The device servershall return the descriptor information for the echo buffer. If there is no echo buffer implemented, the device servershall return all zeros in the READ BUFFER descriptor. The BUFFER OFFSET field is reserved in this mode. Theallocation length should be set to four or greater. The device server shall transfer the lesser of the allocation lengthor four bytes of READ BUFFER descriptor. The READ BUFFER descriptor is defined as shown in table 84.Table 84 — Echo buffer descriptorBitByte7 6 5 4 3 2 1 00 Reserved EBOS1 Reserved2 Reserved (MSB)3 BUFFER CAPACITY (LSB)The BUFFER CAPACITY field shall return the size of the echo buffer in bytes aligned to a four-byte boundary. Themaximum echo buffer size is 4096 bytes.If the echo buffer is implemented then the echo buffer descriptor shall be implemented.An echo buffer overwritten supported (EBOS) bit of one indicates either:a) the target returns the ECHO BUFFER OVERWRITTEN additional sense code if the data being read fromthe echo buffer is not the data previously written by the same initiator, orb) the target ensures echo buffer data from each initiator is the same as that previously written by the sameinitiator.An EBOS bit of zero specifies that the echo buffer may be overwritten by other initiators or intervening commands.dpANS SCSI Primary Commands - 2 (SPC-2) 117