PicoLink Protocol Specification

PicoLink is a simplified directory-based cache-coherency protocol derived from TileLink, using the MESI coherence model over two channels (A: Core → CM, B: CM → Core), with no probe/downgrade messages and no release handshake.

This documentation is the authoritative specification for the PicoLink protocol and its verification IP. Normative requirements are tagged with stable rule identifiers (PL-<AREA>-<NN>); see Introduction for the document conventions.

Contents:

• Introduction
  • About this specification
  • Release information
  • Document conventions
  • Protocol overview
  • System architecture
  • Scope and limitations
  • Relationship to TileLink
• Channels
  • Channel usage rules
  • A channel messages (Core → CM)
  • B channel messages (CM → Core)
  • Grant message usage
  • Request–response summary
• Signal Descriptions and Flow Control
  • Global signals
  • A channel signals (Core → CM)
  • B channel signals (CM → Core)
  • Handshake rules
  • Flow-control and dependency rules
• Message Field Definitions
  • Protocol parameters
  • Common fields
  • A channel message fields (Core → CM)
  • B channel message fields (CM → Core)
  • Transaction identifier rules
• MESI State Transitions
  • State definitions
  • System-wide invariants
  • Transition table
  • Requester rules
  • State diagram
• Coherency Manager (CM) Behavior
  • Directory state
  • Serialization and concurrency
  • Response behavior
  • Grant ordering rules
  • Memory interaction
  • Permitted optimizations
  • Forward progress
• Ordering, Races, and Atomicity
  • Ordering model
  • Atomicity
  • Race conditions
  • Deadlock freedom
• Message Sequence Diagrams
  • Read miss, line uncached
  • Read miss, shared copy exists
  • Read miss, another core holds E
  • Write miss, line uncached
  • Write miss, multiple sharers
  • Write hit on shared line: Upgrade
  • Read while another core is Modified: forced WriteBack
  • Voluntary WriteBack: cache eviction
  • Race 1: dual Upgrade
  • Race 3: Invalidate crosses Upgrade
  • Race 4: voluntary WriteBack crosses Invalidate
• Glossary

Indices

• Index

• Search Page