User Manual

SCSI Commands Reference Manual, Rev. J 409
www.seagate.com Parameters for direct access devices
BUS INACTIVITY TIME LIMIT field
The value in the BUS INACTIVITY TIME LIMIT field contains the maximum period that an SSP target port is permitted to maintain a connection
without transferring a frame to the SSP initiator port. This value shall be the number of 100 ms increments between frames that the SSP target
port transmits during a connection. When this number is exceeded, the SSP target port shall prepare to close the connection (i.e., by request
-
ing to have the link layer transmit DONE). This value may be rounded as defined in 2.3. A value of zero in this field shall specify that there is no
bus inactivity time limit.
MAXIMUM CONNECT TIME LIMIT field
The value in the MAXIMUM CONNECT TIME LIMIT field contains the maximum duration of a connection. This value shall be the number of 100
ms increments that an SSP target port transmits during a connection after which the SSP target port shall prepare to close the connection (e.g.,
a value of one in this field means that the time is less than or equal to 100 ms and a value of two in this field means that the time is less than or
equal to 200 ms). If an SSP target port is transferring a frame when the maximum connection time limit is exceeded, the SSP target port shall
complete transfer of the frame before preparing to close the connection. A value of zero in this field shall specify that there is no maximum
connection time limit. The maximum connection time limit is enforced by the port layer. This value may be rounded as defined in
2.3.
MAXIMUM BURST SIZE field
For read data, the value in the MAXIMUM BURST SIZE field contains the maximum amount of data that is transferred during a connection by an
SSP target port per I_T_L_Q nexus without transferring at least one frame for a different I_T_L_Q nexus. If the SSP target port:
a) has read data to transfer for only one I_T_L_Q nexus, and
b) has no requests to transfer write data for any I_T_L_Q nexus;
then the SSP target port shall prepare to close the connection after the amount of data specified by the MAXIMUM BURST SIZE field is trans-
ferred to the SSP initiator port.
For write data, the value shall specify the maximum amount of data that an SSP target port requests via a single XFER_RDY frame.
This value shall be specified in 512-byte increments (e.g., a value of one in this field means that the number of bytes transferred to the SSP initi-
ator port for the nexus is less than or equal to 512 and a value of two in this field means that the number of bytes transferred to the SSP initiator
port for the nexus is less than or equal to 1 024). The device server may round this value down as defined in 2.3. A value of zero in this field shall
specify that there is no maximum burst size.
In terms of the SCSI transport protocol services, the device server shall limit the Request Byte Count argument to the Receive Data-Out () proto-
col service and the Send Data-In () protocol service to the amount specified in this field.
FIRST BURST SIZE field
If the ENABLE FIRST BURST field in the COMMAND frame is set to zero, the FIRST BURST SIZE field is ignored.
If the ENABLE FIRST BURST field in the COMMAND frame is set to one, the value in the FIRST BURST SIZE field contains the maximum amount of
write data in 512-byte increments that may be sent by the SSP initiator port to the SSP target port without having to receive an XFER_RDY
frame from the SSP target port (e.g., a value of one in this field means that the number of bytes transferred by the SSP initiator port is less than
or equal to 512 and a value of two in this field means that the number of bytes transferred by the SSP initiator port is less than or equal to
1
024).
Specifying a non-zero value in the FIRST BURST SIZE field is equivalent to an implicit XFER_RDY frame for each command requiring write data
where the WRITE DATA LENGTH field of the XFER_RDY frame is set to 512 times the value of the FIRST BURST SIZE field
The rules for data transferred using the value in the FIRST BURST SIZE field are the same as those used for data transferred for an XFER_RDY
frame (i.e., the number of bytes transferred using the value in the FIRST BURST SIZE field is as if that number of bytes was requested by an
XFER_RDY frame).
If the amount of data to be transferred for the command is less than the amount of data specified by the FIRST BURST SIZE field, the SSP target
port shall not transmit an XFER_RDY frame for the command. If the amount of data to be transferred for the command is greater than the
amount of data specified by the FIRST BURST SIZE field, the SSP target port shall transmit an XFER_RDY frame after it has received all of the data
specified by the FIRST BURST SIZE field from the SSP initiator port. All data for the command is not required to be transferred during the same
connection in which the command is transferred.
A value of zero in this field shall specify that there is no first burst size (i.e., an SSP initiator port shall transmit no write DATA frames to the SSP
target port before receiving an XFER_RDY frame).