Hitachi ULTRASTAR 15K450 HUS154530VLF400 - Manual (Page 327)

Hitachi Ultrastar 15K450 (FC-AL) Hard Disk Drive Specification
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The Port retransmits received ARB(F0) and prepares to receive the following frames, followed by CLS.
a. When a LIFA frame is received, the Port will set the bit corresponding to the Port’s “Fabric Assigned” AL_PA if the
Port was logged-in to the local FL_Port prior to the LIP. (See 21.5, “Public Loop Operation” on page 312.) After
transmitting the LIFA frame, The Port waits to receive a LIPA frame.
b. When a LIPA frame is received (and a bit was not set for LIPA), the bit corresponding to any previously assigned
AL_PA is checked. If not set, it is set now. If it is already set, the Port attempts to obtain its Hard AL_PA in step c.
The Port transmits the LIPA.
c. When a LIHA frame is received (and a bit was not set for LIPA), the bit corresponding to any required hard assigned
AL_PA is checked. If not set, it is set now. If it is already set, the Port attempts to obtain a Soft AL_PA in step d. The
Port transmits the LIHA.
d. When a LISA frame is received (and a bit was not set for LIHA), the bit associated with the lowest priority AL_PA
still available is set. This is the Port’s soft assigned AL_PA. If no bits are available, the Port shall stay in non-partici-
pating mode. The Port transmits the LISA.
e. If a LIRP frame is received, and the Port was able to claim an AL_PA in one of the LIxA frames, the left most byte
is incremented by one and used as an offset at which to store the Port’s AL_PA. The Port transmits the LIRP.
f. If a LILP frame is received, the Port may store the AL_PA position map for use in error recovery. The Port transmits
the LILP.
g. When CLS is received, the Port retransmits it and goes to MONITORING state.
21.3 Flow Control
The drive provides a Class 3 service. Flow control is maintained using R_RDYs.
Each initiator is required to login with every target. This establishes the Login BB_Credit, (i.e. how many frames the initiator
or target may send immediately on opening or being opened.)
Prior to login, BB_Credit is zero.
The Alternate BB_Credit Model is operated as follows...
• On opening, the Available BB_Credit in each direction is set to the agreed Login BB_Credit value.
• Each frame sent decrements the Available BB_Credit and each R_RDY received increments it.
• If the Available BB_Credit reaches zero, the node must stop sending frames until enough R_RDYs have been
received to restore positive credit.
• It is permissible to close before credit is balanced (i.e. R_RDY received for each frame sent) but only when enough
buffers are available to satisfy the maximum Login BB_Credit that has been extended.
Available BB_Credit may exceed Login BB_Credit but a point to note is that R_RDY is not specific to any frame type. There-
fore, the amount of Available BB_Credit that the drive will extend is limited by the amount of buffer space available for
FCP_CMND or FCP_DATA IUs. For example, during the execution of a 512K WRITE command, there may be buffer space
for 256 2K FCP_DATA IUs and 10 FCP_CMND IUs. The amount of credit extended will be for 10 frames.
21.4 Login Requirements
In order to communicate effectively, a pair of L_Ports must exchange operational parameters. The same applies to any SCSI
processes that use the L_Ports.
The exchange of parameters is called Login and may be either explicit or implicit.
• Explicit Login is the default. L_Ports use the PLOGI Extended Link Service sequence to exchange parameters and
SCSI Processes use the PRLI Extended Link Service.
• Implicit Login is enabled via setting of mode page 19h. When enabled, PLOGI and PRLI are not required and a
default set of parameters is assumed.