Seagate Ultra160 Product Manual page 226

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[3] Both ratio parameters are the numerators of a fractional multiplier that has 256 (100h) as its denominator.
[4] The BUFFER FULL RATIO indicates, on READ commands, how full the drive's buffer shall be before
attempting a reselection. This value is changeable by a SCSI initiator port, but the value is ignored by the
drive. The drive uses an adaptive algorithm that accounts for the buffer segment size, the command trans-
fer length, and data transfer rate to determine the optimal point to reconnect.
[5] The BUFFER EMPTY RATIO indicates, on WRITE commands, how empty the drive's buffer shall be
before attempting a reselection. This value is changeable by a SCSI initiator port, but the value is ignored
by the drive. The drive uses an adaptive algorithm that accounts for the buffer segment size, the command
transfer length, and data transfer rate to determine the optimal point to reconnect.
[6] The BUS INACTIVITY LIMIT field (bytes 4 & 5) indicates the time, in 100 microsecond increments, the
drive is allowed to assert the Busy signal without handshakes until it shall disconnect. The value of ten
indicates the drive is allowed to maintain the Busy signal for one millisecond without handshakes. A value
of zero indicates that there is no bus inactivity limit. This value is not changeable by the initiator.
[7] The DISCONNECT TIME LIMIT field (bytes 6 and 7) indicates the minimum time, in 100 microsecond
increments, the drive shall remain disconnected until it shall attempt to reconnect. A value of zero indi-
cates the drive is allowed to reconnect immediately. For the typical drive, this is likely to always be zero
and the changeable code is always zero (see individual drive's Product Manual, Volume 1).
[8] The CONNECT TIME LIMIT field (bytes 8 and 9) indicates the maximum time in 100 microsecond incre-
ments that the target should remain connected until it attempts to disconnect. A setting of zero indicates
that the drive is allowed to remain connected indefinitely until it attempts disconnection.
[9] The MAXIMUM BURST SIZE field indicates the maximum amount of data that the drive shall transfer dur-
ing a data phase before disconnecting if the initiator has granted the disconnect privilege. This value is
expressed in increments of 512 bytes (e.g., a value of one means 512 bytes, two means 1024 bytes, etc.).
A value of zero indicates there is no limit on the amount of data transferred per connection.
[10] The Data Transfer Disconnect Control (DTDC) field is intended to define further restrictions on when a dis-
connect is permitted. The various DTDC functions called for by the DTDC Field Codes are given in the
table following.
Data Transfer Disconnect Control
DTDC Description
000b Data transfer disconnect control is not used. Disconnect is controlled by the other fields in this
page.
001b A drive shall not attempt to disconnect once the data transfer of a command has started until all
data the command is to transfer has been transferred. The connect time limit and bus inactivity
limit are ignored during the data transfer.
010b Reserved
011b A drive shall not attempt to disconnect once the data transfer of a command has started until
the command is complete. The connect time limit and bus inactivity limit are ignored once data
transfer has started.
If DTDC is nonzero and the maximum burst size is nonzero, the drive shall return CHECK CONDITION
status. The sense key shall be set to ILLEGAL REQUEST and the additional sense code set to Illegal
Field In Parameter List.
Not all Seagate drive models implement this field. See individual drive's Product Manual, Volume 1, which
indicates if a particular drive implements the DTDC function.
[11] The Enable MODIFY DATA POINTERS (EMDP) bit indicates whether or not the initiator allows the MOD-
IFY DATA POINTERS message to be sent by the target. If the EMDP bit is zero, the target shall not issue
the MODIFY DATA POINTERS Message. If the EMDP bit is one, the target is allowed to issue MODIFY
DATA POINTERS Message.
[12] The optional Disconnect Immediate (DImm) bit of zero indicates that the drive may disconnect after com-
mand phase if it chooses to do so based on its internal algorithms, the setting of the DiscPriv bit in the
IDENTIFY message, and the settings of the other parameters in this mode page.
An optional Disconnect Immediate bit of one indicates that the drive shall attempt to disconnect immedi-
ately after every command phase for those connections in which disconnections are allowed.
SCSI Interface Product Manual, Rev. B