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Maxtor Atlas 10K V 5-95
Table 5-124 READ BUFFER Command-Field Descriptions
Field Description
Mode
Four modes are supported by the drive; Combined Header and Data, Data Only, Descriptor Only, and
Read Data from Echo Buffer. The permissible values for Buffer ID, Buffer Offset, are as follows:
0000b
Combined Header and Data – In this mode, data to be transferred is preceded by a 4-byte header that
contains the buffer capacity. The resulting descriptor and data are transferred to the initiator during the
command’s data-in buffer transfer.
Buffer ID must be 0
Buffer Offset must be 0
Allocation length must be set to between 0 and 516 (4 bytes of header and up to 512 bytes of data).
0010b
Data Only– In this mode, the data-in buffer transfer contains data from the controller’s memory.
Buffer ID. When non-zero, the value specifies a specific track line in the controller’s cache. If Buffer
ID of zero is specified, the buffer referenced is the same as if a Buffer ID of one were specified.
Buffer Offset. When non-zero, the value of Buffer Offset can range from 0 to one less than the number
of sectors/track multiplied by 512. This value must be either a zero or a multiple of 512.
Allocation Length Must be between zero and the maximum number of sectors/track multiplied by 512.
0011b
Descriptor Only
When requesting a descriptor (a description of the buffer referenced in the Buffer IDfield), the resulting
data is the offset boundary requirements and the length of each buffer.
Buffer ID When non-zero, the value specifies a specific track line within the controller’s cache. If Buff-
er ID of 0 is specified, the buffer referenced is the same as if a Buffer ID of 1 were specified.
Buffer Offset Must be zero
Allocation Length Must be between 4 (header) and the maximum number of sectors/track multiplied
by 512 + header size.
1010b Read Data from Echo Buffer
In this mode, the drive transfers data to the host from the echo buffer. The echo buffer will transfer the
same data as when the WRITE BUFFER command with the mode field set to echo buffer was issued.
Buffer ID Ignored.
Buffer Offset Ignored.