Rambus

At Rambus, we create cutting-edge semiconductor and IP products, providing industry-leading chips and silicon IP to make data faster and safer.

MSI (Message Signaled Interrupts)

Table of Contents

  1. Definition
  2. How it Works
  3. Features
  4. Benefits
  5. Enabling Technologies
  6. Rambus Technologies

What is MSI?

Instead of asserting a physical interrupt pin, a device sends a small memory write transaction to a predefined address in the host system. This write contains the interrupt vector, which the processor interprets as an interrupt request. MSI supports multiple interrupt vectors per device, allowing fine-grained signaling and better support for multi-core systems. The enhanced version, MSI-X, expands the number of vectors and adds per-vector masking and configuration.

How MSI works

Instead of asserting a physical interrupt pin, a device sends a small memory write transaction to a predefined address in the host system. This write contains the interrupt vector, which the processor interprets as an interrupt request. MSI supports multiple interrupt vectors per device, allowing fine-grained signaling and better support for multi-core systems. The enhanced version, MSI-X, expands the number of vectors and adds per-vector masking and configuration.

What are the key features of MSI?

  • In-band signaling via PCIe memory writes
  • Support for up to 32 vectors in MSI, and up to 2048 in MSI-X
  • Per-vector masking and configuration in MSI-X
  • Compatible with virtualization and IOMMU
  • Efficient interrupt routing in NUMA systems
 

What are the benefits of MSI?

  • Scalability: Supports multiple interrupts per device, ideal for multi-core and multi-threaded environments.
  • Reduced Latency: Eliminates the need for physical signal propagation, improving response time.
  • Simplified Hardware Design: Reduces pin count and routing complexity.
  • Improved Performance: Enables parallel interrupt handling and better load distribution.
 

Enabling Technologies

MSI is foundational in:

  • PCIe 3.0/4.0/5.0/6.0 systems
  • Operating systems with advanced interrupt handling (e.g., Linux, Windows Server)
  • Virtualization platforms using SR-IOV and VM interrupt routing
  • High-performance NICs, GPUs, and storage controllers
  • Multi-core processors with APIC or x2APIC support
 

Rambus Technologies

Rambus offers PCIe and CXL Controller IP that supports MSI and MSI-X for efficient interrupt signaling in high-speed systems. These IP cores are optimized for low latency and high throughput, making them ideal for data center, AI/ML, and embedded applications.

Back to Glossary

Rambus logo