Open Chiplet Architecture (OAC) Wiki

Open Chiplet Architecture (OCA) is an open standard developed by Tenstorrent to address the growing complexity and interoperability challenges of chiplet-based system design. Unlike monolithic SoCs, chiplet-based systems use multiple smaller dies—called chiplets—that are fabricated independently and integrated into a System-in-Package (SiP). OCA standardizes the interfaces and behaviors across these chiplets to enable seamless multi-vendor interoperability.

OCA promotes a “plug-and-play” chiplet ecosystem, enabling both chiplet designers and package integrators to innovate and collaborate using a common framework.

Motivation

While chiplets offer benefits such as modularity, better yield, cost efficiency, and faster time-to-market, they also introduce complex challenges when integrating components from different vendors:

Domain	Integration Challenge
Interconnect	Differing transport/protocol stacks
Addressing	Non-unified address mapping
Boot	Cross-vendor boot flow coordination
System Management	Distributed control loops
Security	Incompatible security domains and lifecycle control
Interrupts	Inconsistent interrupt delivery
FuSa and RAS	Difficult safety/reliability integration
Debug/Test	No unified debug/test interface
Software	Vendor-specific APIs and protocols

OCA is designed to solve these challenges by providing a layered and standards-based interoperability framework.

OCA Layered Architecture

OCA defines a 5-layer stack to standardize chiplet interaction:

1. Software Layer

Defines the Open Chiplet Management Interface (OCMI) for secure system management and software communication.
Supports a signed image format and shared bootloader interface.
Enables SiP-wide device configuration via common data structures.

2. System Layer

Organizes chiplets into primary and secondary roles.
Provides boot flow orchestration, address translation, and hierarchical system management.
Introduces SSID/DSID for security domain alignment.
Supports IEEE 1838 for post-silicon test, and standard FuSa/RAS interfaces.
Implements hardware-based time synchronization.

3. Protocol Layer

Supports standard communication protocols (e.g., AXI, CHI).
Introduces Open Chiplet Configuration Protocol (OCCP) for boot and management flows.
Allows domain-specific protocol extension.

4. Transport Layer

Supports high-speed interconnects: UCIe and BoW.
Auxiliary transport via I3C/I2C with in-band interrupts for boot, firmware, telemetry, etc.

5. Physical Layer

Defines mechanical, electrical, and thermal integration specs.
Covers 2D, 2.5D, and 3D integration styles.
Standardizes D2D interface design, power delivery, and clock routing.

Profiles

To prevent fragmentation, OCA introduces application-specific profiles:

Data Center Profile
Automotive Profile

Each profile mandates support for a core set of specifications tailored for that domain.

Design Principles

Principle	Description
Open	Based on open standards—avoids vendor lock-in
Standards-Based	Leverages existing, proven industry standards
Accessible	Supports wide IP reuse and independent development

Integration Examples

Figure 1: Inter-vendor SiP Integration

Multi-vendor chiplets integrated using all five OCA layers.
Standardized across interconnects, boot, and management interfaces.

Figure 2: In-house Chiplet Integration

Uses only OCA Software and System layers.
Lower layers (protocol/transport) remain proprietary.

Glossary

Term	Definition
AXI / CHI	Bus/protocols for inter-chiplet communication
BoW	Bunch of Wires – low-latency die-to-die link
UCIe	Universal Chiplet Interconnect Express
DSID / SSID	Dynamic/Static Security Identifiers
FuSa / RAS	Functional Safety / Reliability, Availability, Serviceability
I3C / I2C	Low-speed auxiliary transport
OCCP	Open Chiplet Configuration Protocol
OCMI	Open Chiplet Management Interface

Summary

Open Chiplet Architecture (OCA) represents a major step toward achieving true chiplet interoperability. By standardizing layers from software to physical integration, it enables a scalable, modular, and collaborative ecosystem for chiplet-based system design. Developed and championed by Tenstorrent, OCA opens the door for efficient cross-vendor collaboration and accelerated innovation in semiconductors.