User Manual

SCSI Commands Reference Manual, Rev. J 407
www.seagate.com Parameters for direct access devices
EMDP bit
The enable modify data pointers (EMDP) bit indicates whether or not the target FCP_Port may use the random buffer access capability to reor-
der FCP_DATA IUs for a single SCSI command. If the EMDP bit is set to zero, the target FCP_Port shall generate continuously increasing relative
offset values for each FCP_DATA IU for a single SCSI command.
1 If the EMDP bit is set to one, the target FCP_Port may transfer the FCP_DATA IUs for a single SCSI command in any order.
0 If the EMDP bit is set to zero, data overlay is prohibited even if it is allowed by the state of the PRLI FCP Service Parameter page DATA
OVERLAY ALLOWED bit.
The EMDP bit does not affect the order of frames within a Sequence. The enable modify data pointers function is optional for all FCP devices.
For bidirectional commands, the EMDP bit applies independently to the read operation and write operation. If the EMDP bit is set to zero, the
target FCP_Port shall generate continuously increasing relative offset values for the read operation and the write operation, but there is no
read operation to write operation or write operation to read operation ordering requirement.
FAA, FAB, FAC bits
The fairness access (FA) bits, FAA, FAB, and FAC, indicate whether a target FCP_Port attached to an arbitrated loop (see FC-AL-2) shall use the
access fairness algorithm when beginning the interconnect tenancy.
1 An FA bit set to one indicates that the target FCP_Port shall use the access fairness algorithm for the specified frames.
0 An FA bit set to zero indicates that the target FCP_Port may choose to not use the access fairness algorithm.
The FAA bit controls arbitration when the target FCP_Port has one or more FCP_DATA IU frames to send to an initiator FCP_Port.
The FAB bit controls arbitration when the target FCP_Port has one or more FCP_XFER_RDY IU frames to send to an initiator FCP_Port.
The FAC bit controls arbitration when the target FCP_Port has an FCP_RSP IU frame to send to an initiator FCP_Port.
If the target FCP_Port intends to send multiple frame types, it may choose to not use the access fairness algorithm if any applicable FA bit is set
to zero. FCP devices attached to links that do not have the concept of interconnect tenancy shall ignore the FA bits. The FA bits are optional for
all FCP devices.
FIRST BURST SIZE field
When the WRITE FCP_XFER_RDY DISABLED bit is negotiated as being set to one in the PRLI FCP Service Parameter page, the FIRST BURST SIZE
field indicates the maximum amount of all bytes that shall be transmitted in the first FCP_DATA IU sent from the initiator FCP_Port to the target
FCP_Port. If all data is transmitted in the first IU, no subsequent FCP_XFER_RDY IUs shall be transmitted by the target FCP_Port. If the maximum
amount of data has been transmitted, but more data remains to be transferred, the target FCP_Port shall request that data with subsequent
FCP_XFER_RDY IUs.
When the WRITE FCP_XFER_RDY DISABLED bit is negotiated as being set to zero in the PRLI FCP Service Parameter page, the FIRST BURST SIZE
field is ignored and permission to transmit data from the initiator FCP_Port to the target FCP_Port is managed using FCP_XFER_RDY IUs. For
data transmissions from the target FCP_Port to the initiator FCP_Port, the FIRST BURST SIZE field is ignored.
The FIRST BURST SIZE field value is expressed in increments of 512 bytes (e.g., a value of one means 512 bytes, two means 1024 bytes). A value
of zero indicates that there is no first burst size limit. The FIRST BURST SIZE field shall be implemented by all FCP devices that support the WRITE
FCP_XFER_RDY DISABLED bit being set to one. The application client and device server may use the value of this parameter to adjust internal
maximum buffering requirements.