C141-E054-02EN
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1.2.2
Frame Structure (Refer to FC-PH, Chapter 17)
A frame format is shown in Figure 1.5.
0-2048+64 (optional header)
0-528
6
24
1
word count
4
min6
min24
byte count
fill words
EOF
CRC
Payload
Frame
Header
SOF
fill words
1
4
1
4
Figure 1.5
Frame Format
a)
SOF
; Start of frame indicates the beginning of the frame.
b)
Frame Header ; Used as link control, drive protocol transfer and detect error condition.
The frame header format is listed in Table 1.2.
Table 1.2
Frame header format
word/byte
0 (bits 31 – 24) 1 (bits 23 – 16) 2 (bits 15 – 08) 3 (bits 07 – 00)
0
R_CTL
D_ID
1
reserved
S_ID
2
TYPE
F_CTL
3
SEQ_ID
DF_CTL
SEQ_CNT
4
OX_ID
RX_ID
5
OFFSET
R_CTL
; Routing Control to categorize the frame.
D_ID
; Destination Identifier, N_port address to which the frame is being sent.
S_ID
; Source Identifier, N_port address originating the frame.
TYPE
; Data Structure Type, identifies the frame protocol.
F_CTL
; Frame Control information
SEQ_ID
; Sequence Identifier, uniquely identifies frames in a non-streamed sequence.
DF_CTL
; Data Field Control, specifies the optional headers in the payload.
This field is not supported by the drive and used as 00h.
SEQ_CNT
; Sequence Count, identifies the order of the frames.
OX_ID
; Originator Exchange Identifier, assigned by the originator of an exchange.
This value is similar to Queue Tag in SCSI and must be unique for a
pair between the intiator and the drive.
RX_ID
; Responder Exchange Identifier, generated by the responder for a exchange.
OFFSET
; Defines the relative displacement of the first byte of the payload from
the base address of the command.
c)
Payload
; Data field, must be multiple of four bytes.
–If the frame is FC-4 Device Data, the payload has SCSI CDB,
Read/Write Data or status/sense information.
–If the frame is Link Data, the payload has control information for the
drive or the response data to the initiator.
d)
CRC
; Calculates without including SOF and EOF delimiters.
e)
EOF
; End of frame indicates the end of a frame.
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