Operation Mode Setting - Fujitsu MAX3073NC - SCSI,80, Dell DC961,Hard Drive Scsi Logical Interface Specifications

2.1.2

Operation mode setting

(1) MODE SELECT parameter
In order to make it possible to control from the INIT the reconnection processing start timing for executing
data transfers with the SCSI bus in read and write operations, the IDD is provided with the MODE SELECT
parameter (Disconnect/Reconnect Parameter: Page code = 2) shown in Figure 2.4. The user can set the
optimum operating state in the system environment as necessary. The MODE SELECT parameter held by
the IDD is common to all INITs. Therefore, note that the parameter of each INIT is changed when this
parameter is changed. See Section 3.1.5 for details of the MODE SELECT command.
[Disconnect/Reconnect Parameter (Page code = 2)]
Bit
Byte
0
1
2
3
4
~ ~
~
~
15
Figure 2.4
a. Buffer full ratio
This parameter specifies the timing for the IDD to start reconnection to perform data transfer to the
INIT in a 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. However, if the
total amount of transfer data specified in the command does not fill the capacity of the cache
segment, the IDD executes reconnection processing and begins transferring data to the INIT when it
becomes possible to transfer the amount of data blocks from the data buffer which is equivalent to
the proportion of the total volume of transfer data blocks specified in the command that is specified
by this parameter.
For example, if a read operation of 16 blocks with a logical data block length of 512 bytes (8 Kbytes)
is requested, when the value specified in this parameter is 32, reconnection processing is performed
when it becomes possible to transfer 2 blocks of data [16 x (32/256)], from the data buffer.
C141-C010
7 6 5
0 0 0
X'0E' (Page Length)
Buffer Full Ratio
Default Value: X'00'
Variable Range: X'00' to X'FF'
Buffer Empty Ratio
Default Value: X'00'
Variable Range: X'00' to X'FF'
(Other parameters)
Parameters for controlling reconnection timing
4 3 2
0 0 0
2.1 Data Buffer
1 0
1 0
~
~
2-5