Seagate SCSI Interface Product Manual page 141

SCSI Interface Product Manual, Rev. J
[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 an initiator, 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 incre-
ments, the drive shall remain disconnected until it shall attempt to reconnect. A value of zero indicates 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 increments
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 during 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 Parame-
ter 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 Modify 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 Mes-
sage.
[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.
Host adapters in untagged command environments which have relatively high overhead to handle a Dis-
connect message sequence may want to use the Disconnect Immediate feature. However, not all Seagate
drive models implement this feature. See individual drive's Product Manual, Volume 1.
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