Best-in-class CXL Verification IP for your IP, SoC, and system-level design testing.

The Cadence® Verification IP (VIP) for Compute Express Link (CXL) is part of the Cadence family of VIP for PCI Express® (PCIe®). Built on top of Cadence's mature industry-leading VIP for PCIe, the CXL VIP provides a complete bus functional model for all three CXL protocols,, and allows users to verify both CXL host and device designs for all device types (Type 1 – 3) from the very first days of the CXL protocol.

Designed for easy integration in testbenches at the IP, system-on-chip (SoC), and system level, the VIP for CXL runs on all simulators and supports SystemVerilog along with the widely adopted Universal Verification Methodology (UVM). This enables verification teams to reduce the time spent on environment development, and redirect it to cover a larger verification space, accelerate verification closure, and ensure end-product quality.

With a layered architecture and powerful callback mechanism, verification engineers can verify CXL features at each functional layer (PHY, link, transport, and application layer) and create highly targeted designs while taking advantage of the latest design methodologies for random testing to cover a larger verification space. The VIP for CXL can be used as a standalone and as a platform for running TripleCheck tests and supports the latest PIPE specification.

Supported specifications: Compute Express Link Specification 2.0 revision 1.0 and 3.0 revision 1.0.

CXL diagram

Product Highlights

  • Support testbench language interfaces for SystemVerilog, UVM, OVM, e, and SystemC
  • Generates constrained-random bus traffic with predefined error injection
  • Callbacks access at multiple TX and RX queue points for scoreboarding and data manipulation
  • Dynamic activation support to enable the user to set the VIP as active or passive without changing the testbench while determining the instance to instantiate during run time
  • Extensive SystemVerilog coverage model

Key Features

The following table describes key features from the specifications that are implemented in the VIP:

Feature Name


Device Configuration

  • Host, Device

Spec Version

  • 1.1, 2.0, 3.0

Device Type

  • Type 1: Caching Devices/Accelerators:, CXL.cache
  • Type 2: Accelerators with Memory:, CXL.cache, CXL.mem
  • Type 3: Memory Buffers:, CXL.mem

Protocol Support

  •, CXL.mem, CXL.cache


  • Serial (NRZ, PAM4) and PIPE 5.x, PIPE 6.x

Link Rate

  • Native support of 64GT/s, 32 GT/s, and downgraded support of 16GT/s and 8GT/s

Link Width

  • Native widths (x16, x8, x4) and degraded widths (x2, x1)

Downstream Port Support

  • Root complex integrated endpoint (RCiEP) for CXL 1.1 and EP for CXL 2.0

Register Space

  • Configuration space registers (CXL DVSEC)
  • Control status registers (CXL 2.0 DVSEC)
  • CXL RCRB support for 1.1 backward compatibility testing

FLIT Support

  • CXL 3.0 256B Flit
  • 64B Flit
  • NULL flit
  • transaction mapping in FLIT
  • CXL.mem/cache protocol FLIT
  • CXL.mem/cache control FLIT: RETRY, LLCRD, INIT
  • NOP Flit

Flex Bus Support

  • Alternative Protocol Support
  • Framing and packet layout
  • Framing error handling
  • Physical Layer Latency Optimization (Sync Header Bypass)


  • vLSM/ALMP Low Power

  • Deepest Allowable Power Management (DAPM)
  • Weighted round-robin
  • Arbitration bypass mode
  • ALMP/vLSM bypass


  • CXL 1.1 and 2.0 enumeration
  • Bypass enumeration
  • Auto-enumeration for CXL DVSEC and Memory Mapped register space

  • Configuration space registers
  • Memory-mapped registers
  • Memory type indication on ATS
  • PM messages, credits, and initialization
  • PM VDM
  • Deferrable Memory Write (DMWr) ECN


  • M2S Req/RwD
  • M2S Req/S2M NDR, DRS (Type 2 flow)
  • Forward progressing rules
  • Speculative memory read
  • Memory error reporting
  • QoS telemetry


  • D2H request/response
  • H2D request/response
  • Back-Invalidation Snoops (CXL3.0 feature)
  • Host, Device Bias modes
  • Cache and Snoop filter modelling

Mem/Cache Link Layer

  • CXL 3.0, 2.0/1.1 Flit Slots support
  • Initialization (LLINIT)
  • Retry flow (RRSM, LRSM) for CXL 2.0
  • Retry flow integration with PCIe 6.0 for CXL 3.0
  • ACK/LLCRD forcing
  • Viral and Poison support

Integrity and Data Encryption (IDE)

  • encryption
  • Authentication: DOE/SPDM/CMA for Discovery, Negotiation, Device attestation, Key negotiation, Bypass mode, Containment and Skid mode
  • Error handling
CXL 2.0 ECNs
  • Devices Operating in CXL 1.1 mode with no RCRB
System Plugins
  • System-level scoreboard
  • System Performance Analyzer

Simulation Test Suite

Extensive testsuite, coverage model and verification plan with clear linkage to the specification for simple and fast compliance testing.

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Boost Your CXL Verification From IP to System-Level