Flow Control

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EE_Credit (end to end flow control) are used by Class 1 and 2 services. Decrement by 1 for each frame sent, and only increment when an ACK is received. Maintained by nodes themselves, switch does not participate in credits. ACK_1 used to for end to end flow control

BB_Credit is used by Class 2 and 3 services. R_RDY ordered set replenishes credits. Maintained by switch. Initial value must be non-zero. R_RDY used for buffer to buffer flow control

Alternative BB_Credit is used in arbitrated loop. Assumes no credits are available. When target is opened by initiator, it sends the initiator a series of R_RDY frames to increment credits based on buffers available. Initiators do not have to maintain credit tables for targets, so less overhead.

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