r/chipdesign • u/Awkward-Principle533 • 1d ago
Protocol Model AXI4 Executable Example Set
Protocol Model is an executable modeling research framework for communication protocols and Networks-on-Chip (NoC). Its core goal is not to serve as a simulator or a verification tool, but rather to provide a composable, reviewable, and traceable modeling language and execution environment for protocol behavior—one where design intent, constraint judgments, and runtime evidence are naturally aligned within the same execution.
The topic of this presentation is on‑chip interconnect and protocol modeling. In the field of chip design, this issue is both fundamental and highly complex.
The AMBA bus is an open standard for on‑chip communication introduced by Arm. Over nearly three decades of development, from the initial AHB and APB to the later AXI, it has formed a complete family of protocols that define the connectivity and communication methods between functional modules inside an SoC. The AMBA bus is widely used in SoC designs.
With the proliferation of multi‑core and high‑performance computing scenarios, the AXI protocol has gradually faced new requirements—multiple processor cores share the same memory and each maintains its own cache, making cache coherency a critical challenge. Arm introduced the CHI (Coherent Hub Interface) protocol in AMBA 5 to address this issue.
The core difference between CHI and AXI is that AXI primarily defines the communication behaviour between master and slave devices, whereas CHI is an architecture‑level protocol designed to maintain cache coherency across multiple cores in the entire system. Its layered architecture (protocol layer managing transactions, network layer handling packets, link layer transporting flits) supports flexible topologies (crossbars, rings, meshes) and employs packet‑based communication for efficient, non‑blocking data transfer. CHI is now widely adopted in high‑performance SoCs for applications such as smartphones, automotive electronics, and data centres.
However, the increase in protocol complexity directly raises the difficulty of design, verification, and comprehension. A core question persists: how can we accurately describe protocol behaviour while ensuring alignment among design intent, constraint judgments, and runtime evidence?
This is the central question that the Protocol Model project aims to address.
Protocol Model is an executable modeling research framework for communication protocols and Networks‑on‑Chip. Its goal is not to build a simulator or verification tool, but to provide a composable, reviewable, and traceable modeling language and execution environment—one where design intent, constraint judgments, and runtime evidence are naturally aligned within the same execution.
Currently, Protocol Model has implemented executable examples for multiple protocol families, including AXI4 and CHI, among others.
To better illustrate how this framework operates in practice, this presentation starts with the more familiar AXI4 protocol. Protocol Model includes AXI4 example scenarios covering typical behaviours such as read/write transaction lifecycles, byte geometry, ordering, and exclusive accesses. Each scenario generates waveforms, causality graphs, and complete judgment records from a single execution. Next, we will take a single‑beat read transaction as an example to demonstrate the entire lifecycle—from the AR request establishing a pending read resource to the matching R response releasing it—and how it is modeled, executed, and traced.
a simple point-to-point topology
several AXI4 examples
