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4.1 Mode Parameters
C141-E167 4 - 11
Note:
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 reconnection 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
reconnection processing with the SCSI bus is started. (Note)
If it is possible to transfer the amount of data specified in this parameter to the INIT from the data
buffer, reconnection processing is executed and transfer of data to the INIT begins.
The default value for this parameter is X’00’. The host can also specify X’00’ for this
parameter. If X’00’is specified, the IDD assigns an appropriate value for this parameter that is
determined by IDD.
b. Buffer empty ratio
This parameter specifies the timing for the IDD to start reconnection 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]. (Note)
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 executes reconnection processing, 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.
The default value for this parameter is X’00’. The host can also specify X’00’ for this
parameter. If X’00’is specified, the IDD assigns an appropriate value for this parameter that is
determined by IDD.