Read Data From Echo Buffer (Mode 01010B); Echo Buffer Descriptor (Mode 01011B); Table 113. Echo Buffer Descriptor; Enable Expander Communications Protocol And Echo Buffer (Mode 11010B) - Hitachi HUS151473VL3800 - Ultrastar 73.4 GB Hard Drive Specifications

17.17.4 Read Data from Echo Buffer (Mode 01010b)

In this mode the drive transfers data from the echo buffer. The echo buffer will transfer the same data as when the WRITE
BUFFER command was issued with the mode field set to echo buffer.
WRITE BUFFER command with the mode field set to echo buffer should be sent prior to the READ BUFFER command; oth-
erwise the READ BUFFER command will be terminated with Check Condition status and Illegal Request.
In this mode Read Buffer transfers the specified amount of data or the amount previously written with a Write Buffer using
mode 1010b from the echo buffer, whichever is less.
Issuing a Read Buffer mode 1010b before a Write Buffer mode 1010b will cause indeterminate data to be returned.
The most significant two bytes of the Allocation Length are ignored. The specified amount of data transferred should not be
larger than the echo buffer capacity. The echo buffer capacity may be determined by using Read Buffer mode 1011b. Any
additional data transferred over and above the echo buffer capacity is regarded as indeterminate.
The Buffer ID and Buffer Offset fields are ignored in this mode.
Note: The echo buffer is a separate buffer from the data buffer used with other read buffer modes. It is intended to be used
for domain validation purposes.

17.17.5 Echo Buffer Descriptor (Mode 01011b)

In this mode, a maximum of four bytes of Read Buffer Descriptor information is returned. The drive returns the descriptor
information for the echo buffer. The Buffer Offset field is reserved in this mode and must be zero. The drive transfers the lesser
of the allocation length or four bytes of following Echo Buffer Descriptor.
Table 113: Echo Buffer Descriptor
Byte
7
0
1
2
3
• EBOS (Echo Buffer Overwritten Supported) bit of zero indicates that the echo buffer is shared by all Initiators.
• Buffer Capacity field returns the size of the echo buffer in byte aligned to a 4-byte boundary.

17.17.6 Enable Expander Communications Protocol and Echo Buffer (Mode 11010b)

Receipt of a READ BUFFER command with this mode (11010b) causes a communicative expander to enter the expanded
communication protocol mode. SCSI target devices that receive a READ BUFFER command with this mode shall process it
as if it were a READ BUFFER command with mode 01010b (see 17.17.4 Read Data from Echo Buffer).
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6 5 4
Reserved = 0
Reserved = 0
Reserved = 0
Buffer Capacity
Hitachi Ultrastar 15K147 SCSI Hard Disk Drive Specification
Bit
3 2
(MSB) Buffer Capacity
(LSB)
161
1 0
EBOS=0