Technical information

HGST Ultrastar C15K600 Hard Disk Drive Specification
214
18.21.3
Descriptor (Mode 00011b)
In this mode, a maximum of four bytes of READ BUFFER descriptor information are returned. The drive returns the
descriptor information for the buffer specified by the Buffer ID.
- Buffer ID field should normally be set to zero, indicating the drive data transfer buffer. If any other value is
specified, the results may be unpredictable.
- Buffer Offset field is reserved.
- Allocation Length should be set to four or greater. The drive transfers the allocation length or four bytes of
READ BUFFER descriptor, whichever is less. The allocation length of zero indicates no data is transferred. The
allocation length of greater than zero and less than four (size of the Descriptor) is an invalid request and will
cause the command to be terminated with Check Condition status. The drive shall set sense key to Illegal
Request and additional sense code to Illegal Field in CDB.
The READ BUFFER descriptor is defined in the figure below.
Table 180 Read Buffer Description
Byte
Bit
7
6
5
4
3
2
1
0
Offset Boundary = 0x09
1-3
(MSB)
Buffer Capacity
(LSB)
The value contained in the Buffer Offset field of subsequent WRITE BUFFER and READ BUFFER commands
should be a multiple of two to the power of the offset boundary. The offset boundary is always set to nine, which
indicates Sector Boundaries.
18.21.4
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; otherwise 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.