A source waiting for READY can deadlock with a destination that waits to observe VALID. The waiting deadlock does not require a combinational loop. For the AXI-style interface here, present a retained pending item independently of READY and preserve it until accepted; separately obey the no-combinational-input-to-output timing rule. A buffer must retain every accepted item while backpressure propagates.

Common trap: Spec citation without deadlock explanation.

Count useful bytes on accepted beats over elapsed time, including idle cycles. Correlate request occupancy, data gaps, consumer backpressure and arbitration with the first loss of progress. Check whether tracking capacity or target service limits the same replay, and whether the requested rate exceeds the data-channel ceiling. A stall percentage alone cannot prove which fix will help.

Common trap: Suggesting wider bus or higher clock first.

Both express finite admission capacity. Ready/valid decides acceptance at an edge; a credit protocol advertises typed units that the sender consumes and later receives back or updates. Credit zero and READY low can both block admission, but their timing, accounting and recovery rules are protocol-specific. Debug the relevant pool, units, consumption and return path.

Common trap: Calling credits identical to READY and losing traffic-class or return-accounting rules.