Datasheet

4.1 Control/Sense Commands
C141-C008 4-35
If transfer of this page descriptor is required by the MODE SENSE
or MODE SENSE EXTENDED command, the IDD reports X '0E'
as the page length (byte 1). However, if either X '0E' or X '0A' is
specified for the page length in the MODE SELECT command, the
IDD regards it as if the correct page length was specified. The X
'0A' page length, is provided in consideration of compatibility with
previous models, but it is recommended that the page length X '0E'
be used by the INIT to support expansions in the specifications in
the future.
See Section 2.1, "Data Buffer" concerning specification methods for the "Buffer Full
Ratio" and "Buffer Empty Ratio" parameters in this page descriptor and details of data
buffer operation.
a. Buffer full ratio
This parameter specifies the timing for the IDD to start Loop OPEN
processing in order to transfer data to the INIT by the READ or READ
EXTENDED command.
The value specified in this parameter (n) shows the amount of data read to the
IDD's data buffer from the disk media as a proportion [n/256] of the total
capacity of the data buffer until it opens the loop for transferring the data on
the FC interface is started.
If it is possible to transfer the amount of data specified in this parameter to
the INIT from the data buffer, opens the loop and transfer of data to the INIT
begins.
b. Buffer empty ratio
This parameter specifies the timing for the IDD to start Loop OPEN
processing when it is requested by the INIT to transfer data in the WRITE,
WRITE EXTENDED or WRITE AND VERIFY command.
The value specified in this parameter (n) indicates the size of the empty area
in the IDD's data buffer as a proportion of the total data buffer capacity of the
IDD [n/256].
While the IDD is writing data to the disk media, it is using the data pre-
fetched to the data buffer in order, and when the empty space in the data
buffer reaches the amount specified in this parameter, it opens the loop,
requesting transfer of the succeeding data.
If the total number of bytes in the transferred data block count specified in
the command is less than the capacity of the buffer segment, all the data are
pre-fetched in a batch, so the specification in this parameter is not applied.