Seagate Fibre Channel Interface User Manual
Page 41
Fibre Channel Interface Manual, Rev. D
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RX_ID (Responder Exchange Identifier)
This 2-byte identifier is a unique identifier generated by the responder for an exchange established by an originator and
identified by an OX_ID.
With Class 3 devices such as this drive, the responder of the exchange assigns a unique value for RX_ID other than FFFFh
if RX_ID is being used in an ACK to a data frame in the first sequence transmitted as a sequence initiator.
The drive returns FFFFh in this field to indicate the RX_ID is not being used.
SEQ_CNT (Sequence Count)
This 2-byte field identifies the sequential order of frames within a sequence or multiple sequences of the same exchange.
The SEQ_CNT value for each frame of a sequence has to be unique. The field range limits the number of frames per
sequence to a maximum of 65,536.
For SCSI FCP write data transfers that require more than one sequence to transfer the data, the first frame of each
sequence starts with a SEQ_CNT of 0000h. The transfer of sequence initiative between write data sequences and the
XFR_RDY sent by the drive give the sequence originator (the SCSI Initiator) verification that the previous sequence is
closed.
For SCSI FCP read data transfers that require more than one sequence to transfer the data, the SEQ_CNT does not reset
to 0000h for each new sequence. The SEQ_CNT increments sequentially across the sequence boundaries. The
SEQ_CNT is still allowed to increment through all 65,536 possible values for each sequence. This is required as there is no
verification in Class 3 that all the frames of previous sequences have been delivered.
SEQ_ID (Sequence Identifier)
This field uniquely identifies frames in a non-streamed sequence or when only one sequence is open.
S_ID (Source Identifier)
The 3-byte address of the N_Port or F_Port originating the frame.
Type (Data Structure Type)
This 1-byte field identifies the protocol of the frame contents as described below:
1000
0000
No operation
Not supported
0001
Abort sequence (ABTS)
Request
0010
Remove connection
Not supported
0011
Reserved
Not supported
0100
Basic_Accept (BA_ACC)
Reply
0101
Basic_Reject (BA_RJT)
Reply
0110-
0111
Reserved
Not supported
Table 11:
Data type codes
R_CTL
(4 highest order bits)
Type code
Description
1000
00
Basic Link Service
0010
01
Extended Link Service
0000
08
SCSI FCP
Table 10:
Routing Control values (Continued)
High order bits
Low order bits
Use