Link Layer

Link Layer is a Workstream under the Open Chiplet Economy (OCE) Sub-Project of the OCP Server Project. The Sub-Project brings the modularization trend that reshaped data center hardware to the foundations of computing, applying open collaboration and standardization across the scope of chiplets. This workstream focuses on the die-to-die (D2D) Link Layer interface and its implementations. Details about the workstream’s mission, scope, and ways to get involved will be added in the near future.

Call for Participation (CFP) Open Framework for Chiplet Eco-system Virtual Prototyping

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Steering Committee Representative

Gregory D Sellman

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About This Workstream

Workstream Leads: Brian Murray

Link Layer is a Workstream under the Open Chiplet Economy (OCE) Sub-Project of the OCP Server Project.

The Open Chiplet Economy Sub-Project brings the modularization trend that reshaped data center hardware to the foundations of computing, applying open collaboration and standardization across the scope of chiplets.

This workstream focuses on the die-to-die (D2D) Link Layer interface and its implementations.

Details about the workstream’s mission and ways to get involved will be added in the near future.

Scope

This workstream focuses on the die-to-die (D2D) Link Layer interface and its implementations.

The full scope of this workstream will be added in the near future.

Resources

Operating under the OCP Server Project’s Open Chiplet Economy Sub-project umbrella.

General Information

The Link Layer Working Group is focused on creating solutions to bridge Systems on Chip busses across die-to-die PHY connections. Initially focused on enabling BoW-based implementations, the Transaction and Link layers provide a way to generally packetize data and a way to map the connection to bus protocols.

Transaction and Link Layer (TLL)

  • Version 1.0 Transaction and Link Layer Specification (OCP) (REPO)
    • The first version of the TLL specification describes a protocol stack for mapping bus protocols to the BoW physical layer. The specification features multi-channel bus protocol transaction packetization, optional ECC support, link granulation, and mapping of said granules to the PHY.
  • Version 1.2 Transaction and Link Layer Specification (REPO)
    • This version is primarily focused on added a protocol stack that supports BoW sideband slices for the purpose of assisting in the bringup and management of the BoW mainband PHYs.
    • NOTE: The spec is complete, but still going through the OCP contribution process.
  • Version 2.0 Transaction and Link Layer Specification (WORKING DIRECTORY)
    • The Link Layer Working Group is currently focused on closing Version 2.0 of the Transaction and Link Layer Specification. This version is focused on two main features
      • Universal TLL: Mapping the TLL to other PHY layers. The 2.0 spec will include both UCIE and BoW.FLEXI
      • Performance enhancements: Trimming the formats to remove unneeded reserved bits, removing some restrictions on TLP to LLP mapping, and expanding the LLP size options.

Profiles

The Transaction and Link Layer Specification requires a number of choices and implementation decisions to be known on both sides of a D2D link. The specification calls for this information to be documented in an ‘Interface Profile’ document. The link below is to a folder holding a number of example profiles that users can reference for creating their own profiles.

Variants

Interface Profiles may need to document multiple different types of bus protocols that are mapped to a given D2D interface. To save effort, increase compatibility, and provide clearer documentation, Interface Profiles may reference existing bus protocols mappings in separate documents known as ‘Bus Protocol Variants’. The Link Layer Work Group has created a number of example Variants in the below link:

Past Call Recordings

Link Layer calendar