CocoTB Framework · Verification Infrastructure for RTL Testing
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AXI4-ACE Components¶

The AXI4-ACE components extend the framework's AXI4-Full BFMs with the ACE coherency extensions: three snoop channels (AC, CR, CD), snoop-type fields on the front-side AR/AW channels, and the RACK/WACK acknowledge handshakes. They are built on the same GAXI infrastructure as the rest of the framework, so field configuration, signal resolution, and statistics behave the same way.

This family implements the cache-ip ACE-shaped port contract: the six transaction types of the onyx D2 research subset, single shareability domain, no barriers or DVM. ACE-Lite masters are not modeled.

Component Overview¶

Core Interface Components¶

AXI4ACEMasterRead - Coherent read master (AR/R) with ARSNOOP and RACK
AXI4ACEMasterWrite - Coherent write master (AW/W/B) with AWSNOOP and WACK
AXI4ACESnoopSlave - Cache-side snoop responder (AC in, CR/CD out)
AXI4ACESnoopMaster - CCU-side snoop initiator (AC out, CR/CD in)

Data Structures and Configuration¶

ACEPacket - Packet class extending AXI4Packet with AC/CR/CD factory methods
SnoopPacket - Convenience container for a complete snoop transaction result
AXI4ACEFieldConfigHelper - Channel field configurations for ACE
ARSnoop / AWSnoop - Front-side ARSNOOP / AWSNOOP encodings (IHI 0022H.c Tables D3-7, D3-8); ACETransactionType is the deprecated combined form
SnoopType - ACSNOOP encodings for the snoop address channel
CRRESP - Bitfield helper for the snoop response
CacheState - Gem5-style MESI states for the default responder

Verification¶

ACEComplianceChecker - Snoop-order and CRRESP validity checker

Key Features¶

ACE Protocol Support¶

Complete front-side AR/AW/W/B/R channel reuse from AXI4, plus ARSNOOP[3:0] and AWSNOOP[2:0]
Three snoop channels: AC (snoop address), CR (snoop response), CD (snoop data)
RACK/WACK auto-pulse when the BFM is constructed as master and the pin exists
Default MESI responder matrix in AXI4ACESnoopSlave

GAXI Infrastructure Integration¶

One field configuration system across the framework
Automatic signal resolution across naming conventions
Multi-level debug and transaction logging
Statistics collected as tests run

Verification Features¶

Programmable snoop handler via set_handler
Cache-line state programming via set_line_behavior
Lightweight compliance checker for snoop ordering and CRRESP validity

Getting Started¶

from CocoTBFramework.components.ace import (
    AXI4ACEMasterRead,
    AXI4ACEMasterWrite,
    AXI4ACESnoopMaster,
    AXI4ACESnoopSlave,
)

# Coherent front-side masters
master_read = AXI4ACEMasterRead(
    dut=dut,
    clock=clk,
    prefix="m_axi_",
    data_width=64,
    id_width=4,
    addr_width=32,
)

master_write = AXI4ACEMasterWrite(
    dut=dut,
    clock=clk,
    prefix="m_axi_",
    data_width=64,
    id_width=4,
    addr_width=32,
)

# Snoop-channel BFMs
snoop_master = AXI4ACESnoopMaster(
    dut=dut,
    clock=clk,
    prefix="m_axi_",
    data_width=64,
    addr_width=32,
)

snoop_slave = AXI4ACESnoopSlave(
    dut=dut,
    clock=clk,
    prefix="fub_",
    data_width=64,
    addr_width=32,
)

Protocol Architecture¶

ACE reuses AXI4's five channels and adds three snoop channels:

graph TB
    subgraph Front["Front-Side (AXI4 + snoop type)"]
        AR["AR + ARSNOOP"]
        R["R"]
        AW["AW + AWSNOOP"]
        W["W"]
        B["B"]
    end

    subgraph Snoop["Snoop Channels"]
        AC["AC - Snoop Address"]
        CR["CR - Snoop Response"]
        CD["CD - Snoop Data"]
    end

    subgraph Ack["Acknowledge Pulses"]
        RACK["RACK"]
        WACK["WACK"]
    end

Documentation Structure¶

Overview - Architecture, D2 subset, default responder matrix, and quickstart examples
Interfaces - API reference for the four BFM classes and factory functions
Packet / Transaction - ACEPacket, SnoopPacket, enumerations, and CRRESP helper
Compliance - ACEComplianceChecker and violation types

cocotb Support¶

Validated on cocotb 1.9.2 and cocotb 2.x.

Everything above is covered in depth in the pages linked from this index — start with the overview if you're new to the component set, or jump straight to the interface references if you just need a signature.