Glossary comparison
ACE vs CHI: what is the difference?
The difference
The Coherent Hub Interface, introduced with AMBA 5, is a separate protocol for connecting fully coherent processors to high-performance, non-blocking interconnects such as Arm's CMN-600. It is the route for high-end designs rather than a newer version of ACE.
ACE, the AXI Coherency Extensions from AMBA 4, adds coherence signalling to AXI, and ACE-Lite gives one-way coherence for devices such as network interfaces. Arm now lists the ACE specification as superseded by CHI.
The two terms
ACE
The AMBA extension that adds snoop channels and cache state signalling to AXI, allowing multiple caching masters to maintain hardware coherency over a shared interconnect.
CHI
Arm's packet-based, layered AMBA protocol for scalable coherent interconnects, designed for many-core and server systems with directory-based coherency and credit-controlled flow.
Side by side
| Field | ACE | CHI |
|---|---|---|
| Stands for | AXI Coherency Extensions | Coherent Hub Interface |
| Type | Acronym | Acronym |
| Domain | Design & Architecture | Design & Architecture |
| Group | Interconnect and fabric | Interconnect and fabric |