Transfer Ready Information Units; Data Information Unit; Response Information Unit - Sun Microsystems storagetek sl500 Reference Manual

Transfer Ready Information Units

The Transfer Ready Information Unit (I1) is a single-frame sequence.
For write operations:
The FCP_XFER_RDY is sent before each write data sequence.
For read operations:
The FCP_XFER_RDY IU (I2) is not used during read type (data in) operations. This
is indicated by setting the 'READ XFER_RDY DISABLED' bit during process login.

Data Information Unit

The Data Information Units (T6 and I3) are either single- or multiple-frame
sequences.
The FCP_DATA IU transfers data associated with an operation. This data includes
command parameter data (such as Mode Select data) or command response data
(such as Mode Sense data).

Response Information Unit

The Response Information Units (I4) are single- or multiple-frame sequences.
The first two bits (30 and 31) of the first word of a command status frame payload
fall into the following categories:
00 = Successful and complete
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01 = Successful but incomplete
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10 = Unsuccessful but complete
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11 = Unsuccessful and incomplete
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Because the first word of FCP_RSP frames are reserved in FCP, these bits are set to
0b, regardless of the content of the SCSI Status portion of the payload. SCSI
initiators do not rely on word 0, bits 31 and 30 in FCP_RSP to determine success or
completion status of a command. An FCP_RSP following a data-in sequence (I3)
may or may not be treated as a streamed sequence.
Residual Checking
Residual checking falls under the following categories:
SCSI targets that transfer exactly FCP_DL data bytes during the FCP_DATA IUs
■
set the FCP_RESID_UNDER to a value of 0b.
When FCP_RESID_UNDER is set to 0b, the SCSI initiator tries to determine if all
of the expected data was transferred by comparing the FCP_DL to the actual
number of bytes transferred. If these values are not the same, the ULP is notified
so that the appropriate action can be taken.
SCSI targets that transfer less than FCP_DL data bytes during the FCP_DATA
■
IUs set the FCP_RESID_UNDER to a value of 1b.
96122 • Revision: F
FC-4 (FCP) Features
Chapter 5 Fibre Channel Operations 73