Disconnect/Reconnect Parameters); Page - IBM DCAS-32160 - Ultrastar 2.1 GB Hard Drive Specifications

7.12.3 Page 2 (Disconnect/Reconnect Parameters)
7 6
BYTE 0 PS RSVD=0
BYTE 1
BYTE 2
BYTE 3
BYTE
4 15
Figure 77. Page 2
Changeable Parameter
Read Buffer Full Ratio
Write Buffer Empty Ratio
The disconnect / reconnect page provides the initiator the means to tune the performance of the SCSI bus.
An initiator may use the IDENTIFY message to grant the file the general privilege of disconnecting. (Dis-
connect requests may still be selectively rejected by the initiator by issuing a MESSAGE REJECT).
The file uses the disconnect/reconnect parameters to control reconnection during REA D ( operation code
08h and 28h) and WRITE ( 0Ah , 2Ah and 2E).
Read Buffer Full Ratio is the numerator of a fraction whose denominator is 256. The fraction indicates
how full the file data buffer should be before attempting to reconnect to the SCSI bus. If the ratio is set
to 0h, the target will calculate and use an optimal ratio based on the negotiated transfer rate.
Write Buffer Empty Ratio is the numerator of a fraction whose denominator is 256. The fraction indi-
cates how empty the file data buffer should be before attempting to reconnect to the SCSI bus. If the
ratio is set to 0h, the target will calculate and use an optimal ratio based on the negotiated transfer rate.
Both the Read Buffer Full Ratio and the Write Buffer Empty Ratio pertain to the current active notch. For
each active notch, as defined in page 0Ch, there are separate Read Buffer Full Ratios and Write Buffer
Empty Ratios. When the active notch is zero, the values are applied across all notches.
7.12.3.1 Reconnection to a disconnected read command
For a read command, the reconnect is delayed relative to the availability of the first block in the file data
buffer by the fraction of the file data buffer size. If the remaining data transfer length is less than the fraction
of the file data buffer size, the file control program calculates the optimal reconnection point to complete the
data transfer as early as possible while minimizing the time connected to the SCSI bus.
106
O E M Spec. of DCAS-34330/32160
BIT
5 4 3 2
Page Code = 02h
Page Length = 0Eh
Read Buffer Full Ratio
Write Buffer Empty Ratio
Reserved = 0
Default Value
00h
00h
1 0