Sun Oracle Storage Tek T10000, Reference Manual

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Arbitrated Loop Feature Set
24 T10000: Interface Reference Manual • January 2011 • E20425-01
Login_BB_Credit Equals Zero
StorageTek tape drives advertise Login_BB_Credit =0. When
Login_BB_Credit=0 at the other L_Port, the following rules apply:
• The OPN originator must receive R_RDYs (receiver readys) from the tape
drive before transmitting a frame.
• The OPNed responder transmits R_RDYs for the number of buffers
available to receive frames.
Note: OPN Originators open as either full or half duplex regardless of the
value of the Login_BB_Credit.
Open and Close Latencies
When Login_BB_Credit=0, a latency exists while waiting for the tape drives to
respond with two (2) R_RDYs. This exists for every OPN before frame
transmission can begin.
To improve the latencies 2-4 and 3-5, and StorageTek tape drives immediately
respond with at least 2 and as many as 5(depending on drive) R_RDYs on an
OPN. This is controlled by a configuration item.
Some NL_Ports reduce CLS latency in another way:
To prevent buffer overruns, a CLS Recipient is only required to have maximum
Login_BB_Credit, granted to any L_Port buffers, available before receiving the
next OPN.