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A RCD (Read Cache Disable) bit of zero indicates that the controller may return
data requested by a READ command by accessing either the cache or media (if the
requested data has not been cached yet).
A RCD bit of one indicates that the controller shall transfer all requested data by
accessing the media without using pre-fetched data.
When RCD bit is set to 1, the data pre-fetched before becomes invalid.
Demand Read Retention Priority specifies the priority of a read data to be retained
in the cache after the read data has transferred to the host computer yet.
Since the controller does not support this field, there should be 0
Write Retention Priority specifies the priority of a write data to be retained in the
cache after the write data has written into the media yet.
Since the controller does not support this field, there should be 0
Disable Pre-fetch Transfer Length specifies maximum data block number to be
pre-fetched. If the data block number requested by a READ command is greater
than the number specified in this field, the surpassed number of blocks will not be
pre-fetched.
If this field is set to 0
Minimum Pre-fetch specifies the minimum number of data to be pre-fetched prior
to executing subsequent commands.
The subsequent commands shall be waited to execute till the number of data
specified in this field will have been pre-fetched.
Maximum Pre-fetch specifies the maximum number of data to be pre-fetched if
there is no subsequent commands.
The data number to be pre-fetched is specified is MF field as either a number of
blocks or a scalar multiplier of the transfer length.
If the data block number requested is greater than the cache (segment) size, the
controller will pre-fetch the partial data which is the full size of cache (segment)
and will not pre-fetch the surpassed data.
Maximum Pre-fetch value shall be equal to or greater than Minimum Pre-fetch
value.
However, the maximum pre-fetch count is determined by the segment size because
the controller uses cache memory divided into segments.
Note :
When the error occurs during pre-fetching, the controller will stop pre-
fetching. This case is not regarded as the error to be informed to the host.
Maximum Pre-fetch Ceiling specifies an upper limit on the number of logical
blocks computed from the Maximum Pre-fetch.
MODE SELECT:(15h)
5 COMMAND DESCRIPTIONS
, the pre-fetch will not be executed.
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Revision: 1 / Date: 2003.03.06
Page: 141 / 273
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