Coupling channel path selection

Each coupling channel type is assigned to a performance selection tier. Those channels with native like performance characteristics occupy the same tier. There is no order within a tier. The tiers themselves are ordered with respect to performance. The assignment is made at the time channel initialization is completed. Channels in a mixed control unit will be assigned to different performance groups or tiers

Message path selection has an approach to use every available buffer of a channel in a higher performance tier before selecting any buffers from channels in a lower performance tier. When multiple channels within tiers are selectable, the firmware implements a round robin selection within those channels so that a single channel within a performance group is not over utilized and all paths within a tier see approximately equal usage.