Home: IP Portfolio > Verification IP > Simulation VIP > VIP for Compute Express Link (CXL)

VIP for Compute Express Link (CXL)

The Cadence® Verification IP (VIP) for Compute Express Link (CXL) is part of the Cadence family of verification IP for PCI Express® (PCIe® ). Built on top of the PCIe 5.0 PHY infrastructure, CXL is an open industry standard for high-bandwidth, low-latency interconnects. It defines the connectivity between the host processor and accelerators/memory devices and smart NICs.

Cadence's VIP for CXL leverages Cadence's mature industry-leading VIP for PCIe. Built on top of an industry-known and -proven platform that was designed for easy integration in testbenches at the IP, system-on-chip (SoC), and system level, the CXL VIP runs on all simulators and supports SystemVerilog along with the widely adopted Universal Verification Methodology (UVM). This enables verification teams to reduce time spent on environment development, and redirect the saved time 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.


Specification Support

The VIP is compliant with Compute Express Link Specification revision 1.1

The specification can be downloaded only by members of the Compute Express Link (CXL) Consortium: https://www.computeexpresslink.org/

Protocol Features

Important features offered in the Cadence VIP for CXL 1.1 are listed below

Feature Name

Device Configuration

Host, Device

Device Type

Type 1: Caching Devices/Accelerators

  • CXL.io

  • CXL.cache

Type 2: Accelerators with Memory

  • CXL.io

  • CXL.cache

  • CXL.mem

Type 3: Memory Buffers

  • CXL.io

  • CXL.mem

Protocol Support






Link Rate

Native support: 32 GT/s

Downgraded support: 16GT/s and 8GT/s

Link Width

Native widths (x16, x8,x4)

Degraded widths (x2, x1)

FLIT Support

  • NULL flit

  • CXL.io transaction mapping in FLIT

  • CXL.mem/cache protocol FLIT

  • CXL.mem/cache control FLIT

    • RETRY

    • LLCRD

    • INIT

Flex Bus Support

  • Alternative Protocol Support

  • Framing and packet layout

  • Recovery.Idle

  • Config.Idle

  • Framing error handling


Weighted round-robin



Bypass enumeration


Compares read data with expected data based on none/any/many trigger(s) happening for that address

Configuration space registers

Memory-mapped registers

Memory type indication on ATS


  • M2S Req/RwD


  • M2S Req/S2M NDR (cache-related)

  • Froward progressing rules


  • D2H request/response

  • H2D request/response

  • Cache-ability details and request restriction

Mem/Cache Link Layer

  • Initialization

  • Retry flow

  • ACK/LLCRD forcing

  • Remote Retry State Machine (RRSM)

  • Local Retry State Machine (LRSM)



  • BIfurcation:Testbench solution

Other Supported Features

Feature Name

UVM Agent


Trace Debug


Training, Documentation, and Usage Information