CXL 2.0 Controller with AXI

Overview

The Compute Express Link™ (CXL™) 2.0 Controller (formerly XpressLINK) leverages a silicon-proven PCIe 5.0 controller architecture for the CXL.io path, and adds CXL.cache and CXL.mem paths specific to the CXL standard. The controller exposes a native Tx/Rx user interface for CXL.io traffic as well as an Intel CXL-cache/mem Protocol Interface (CPI) for CXL.mem and CXL.cache traffic. There is also an CXL 2.0 Controller with AXI version (formerly XpressLINK-SOC) for ASIC and FPGA implementations with support for the AMBA AXI protocol specification for CXL.io and either CPI or AXI for CXL.mem, and CPI for CXL.cache or the AMBA CXS-B protocol specification.

How the CXL 2.0 Controller Works

The controller supports the CXL 2.0 specification and is backward compatible with CXL 1.1. It complies with the Intel PHY Interface for PCI Express (PIPE) specification version 5.x. The provided Graphical User Interface (GUI) Wizard allows designers to tailor the IP to their exact requirements, by enabling, disabling, and adjusting a vast array of parameters, including CXL device type, PIPE interface configuration, buffer sizes and latency, low power support, SR-IOV parameters, etc. for optimal throughput, latency, size and power. The controller has been extensively verified using commercial and internally developed VIP and test suites. It can be paired with a number of 3rd-party CXL PHYs.

The CXL 2.0 controller has been extensively verified using commercial and internally developed VIP and test suites.

Key Features

CXL Protocol Layer
- Comprises complete CXL 2.0 interconnect subsystem with Rambus CXL 2.0 PHY
- Supports the CXL 2.0 specification; backward compatible with CXL 1.1 specification
- Implements the CXL.io, CXL.mem, and CXL.cache protocols
- Supports all 3 defined CXL device types
- Supports the PCI Express 5.0 base specification revision 1.0
- Supports the PIPE 5.x specification with 8, 16, 32, 64 and 128-bit configurable PIPE interface width
- Supports CXL device configurations
- Supports operation at x16, x8, x4, x2, x1
- Supports Host, Device, and Dual Mode/shared silicon implementation
- Supports Low-latency CXL.mem flit encoder/decoder
- Supports Viral error containment
- Supports deferrable writes
- Supports Standard Intel CPI interface or AMBA AXI for CXL.mem
- Supports Standard Intel CPI interface for CXL.cache
- Supports AMBA® CXS.B interface
- Supports Sync header bypass and drift buffer modes supported
- Supports All low-power states
- Supports CXL RAS features (including Viral and Data Poisoning)
- Supports Hot-Plug
- Supports Alternate Protocol Negotiation
- Supports RCiEP
- Supports DOE, CMA over DOE
AMBA AXI Layer for CXL.io
- Compliant with the AMBA® AXI™ Protocol Specification (AXI3, AXI4 and AXI4-Lite) and AMBA® 4 AXI4-Stream Protocol Specification
- Optional AXI4-Lite Slave interface for Bridge Configuration
- Optional AXI4-Lite Master interface for External Registers Configuration
- Optional AXI4 Master Descriptor interface to access SG-DMA Descriptors in AXI domain
- Up to 4 AXI4 Master interfaces, each supporting up to 128 outstanding read requests
- Up to 4 AXI4 Slave interfaces, each supporting up to 256 outstanding read requests
- Up to 4 AXI4 Stream Input and Output interfaces, each handling up to 8 TID/TDEST combinations simultaneously
- 64-bit, 128-bit, 256-bit, or 512-bit data support for AXI4 Master, Slave, and Stream interfaces
- Bypassable CDC for AXI4 Master, Slave, and Stream interfaces
- AXI4 Master and Slave interfaces can be configured as AXI3 interfaces
- Optional built-in Legacy DMA engine
  - Up to 8 DMA channels, Scatter-Gather, descriptor prefetch
  - Completion reordering, interrupt and descriptor reporting
- Optional Address Translation tables for direct PCIe to AXI and AXI to PCIe communication
Integrity and Data Encryption (IDE)
- AES-GCM security supports CXL.mem/CXL.cache at full line rate and with zero latency
- AES-GCM security IP supports PCIe/CXL.io to near full line rate with low latency
- Implements the CXL 2.0 IDE specifications for CXL.cache/mem
- Implements the PCI Express IDE ECN for CXL.io
- Configurable IDE engine
  - Supports x1 to x16 lanes
  - Supports all device types
  - 256-bit or 512-bit data bus for PCIe IDE
  - 512-bit data bus for CXL.cache/mem IDE
- Supports containment and skid modes
- Supports early MAC termination
- Supports multi-stream
- Utilizes high-performance AES-GCM for encryption, decryption, authentication
- PCIe IDE TLP aggregation for 1, 2, 4, 8 TLPs
- PCIe IDE automatic IDE prefix insertion and detection
- PCIe IDE automatic IDE sync/fail message generation
- PCRC calculation & validation
- Efficient key control/refresh
- Bypass mode

Benefits

Internal data path size automatically scales up or down (256, 512 bits) based on max. link speed and width for reduced gate count and optimal throughput
Dynamically adjustable application layer frequency down to 8Mhz for increased power savings
Optional MSI/MSI-X register remapping to memory for reduced gate count when SR-IOV is implemented
Configurable pipelining enables full speed operation on Intel and Xilinx FPGA, full support for production FPGA designs (when supported)
Ultra-low Transmit and Receive Buffer latency
Use of highly optimized CPI interface for CXL.cache and CXL.mem to maximize throughput and minimize latency
Merged Replay and Transmit buffer enables lower memory footprint
Optional QuickBoot mode allows for up to 4x faster link training, cutting system-level simulation time by 20%

Block Diagram

Video

Demonstration of a CXL Interconnect on a FPGA-based design

In this video, we demonstrate the Rambus Controller IP for CXL 2.0 and the CXL.mem protocol used to access Host-managed Device Memory, or HDM. This demonstration is performed using Intel’s Pre-Production Xeon processor as a host, connected to an FPGA board, instantiating Rambus' CXL Controller and CXL.mem test design.

Applications

HPC,
Cloud Computing,
AI,
Machine Learning,
Enterprise,
Networking,
Automotive,
AR/VR,
Test and Measurement

Deliverables

IP files
- Verilog RTL source code
- Libraries for functional simulation
- Configuration assistant GUI (Wizard)
Verification Environment
Documentation
Reference Design
- Synthesizable Verilog RTL source code
- Simulation environment and test scripts
- Synthesis project & constraint files

Technical Specifications

Foundry, Node

Any

Maturity

In production

Availability

Available

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