Overview / K → L

Issue L adds no signals — it adds a transport

Every AXI issue up to K carried every beat with the same VALID/READY handshake. Issue L keeps the five channels and their signal lists unchanged, and instead introduces an alternative credit-based transport, selected by a new AXI5 property. Flow control moves from reactive (wait for READY) to proactive (spend a pre-granted credit).

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AXI_Transport · property

New AXI5 property. Default keeps VALID/READY; when set, the interface runs credit-based transport. Not available in AXI3/AXI4.

caveat · wakeup

When credit-based transport is enabled, wakeup_signal is not supported — credit exchange itself carries the activity information.

Transport / Handshake vs Credits

Two ways to move a beat

The VALID/READY handshake negotiates capacity per beat, in the moment. Credit-based transport negotiates it ahead of time: a held credit is a standing promise that a buffer slot exists, so the sender never waits on READY.

Attribute

VALID / READY

Credit-based

Credits / Grant · Spend · Return

The life of a credit

Step through one credit pool. The receiver grants credits up front; each request the sender issues spends one; when the pool hits zero the sender stalls until the receiver frees a slot and returns a credit. Per Resource Plane the receiver may grant 1–15 credits, plus up to 15 shared.

credits available

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step {{ creditStepNum }} / {{ creditStepTot }}

Resource Planes / Multi-RP interleave

Many planes, one physical channel

A Resource Plane (RP) is an independent credit context that shares the physical wires. Because every beat carries its RP number, write-data beats from different planes can interleave on one W channel — something AXI3 forbade. Each column below is one shared beat; read top-to-bottom to see which plane owns it.

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Reference / Issue timeline

J → K → L

Where Issue L sits in the AMBA 5 AXI line. K was a feature release (MEC, MPAM, MTE); L is a transport release.

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Reference / Cheat sheet

Credit transport at a glance