Easyi3C is a leading supplier of embedded system tools that simplify the development and debugging of various communication protocols. The company offers a range of products designed to help engineers and developers use I3C/I2C , USB and MIPI, JEDEC, MCTP and other protocols more efficiently.
1. Background Introduction to I3C Hub Cascade
Cascading I3C Hubs is a design technique used to expand the number of connected devices, increase signal reach, and manage complex bus topologies in next-generation server and data center architectures. By connecting the downstream (target) port of one hub to the upstream (controller) port of another, developers can build an I3C Hub Network that supports high-density device environments while maintaining the standard's 12.5 MHz performance.
Key Benefits of Cascading
Port Expansion: Standard hubs typically offer 4 to 8 downstream ports; cascading allows for a significantly higher number of total target devices.
Extended Reach: Each hub acts as a buffer or re-driver, isolating bus capacitance and allowing the I3C signal to travel further across large backplanes or between different boards.
Voltage Translation: Cascaded levels can operate at different voltage domains (e.g., 1.0V to 1.98V), enabling communication between a high-voltage controller and low-voltage peripheral sensors.
Logical Isolation: Hubs can isolate segments of the bus to prevent a single faulty device from crashing the entire network, a feature critical for high-availability systems.
Common I3C Hub Solutions
Major semiconductor manufacturers provide hubs specifically designed for this "cascade and duplicate" methodology:
Renesas RG3MxxB12B1 Family: Features 2 upstream and up to 8 downstream ports. It is explicitly documented to support cascading to build extensive hub networks.
NXP P3H2x4xHN Series: Designed for Intel, AMD, and ARM-based servers, these hubs support transparent pass-gate modes for I3C and bridge modes for legacy I2C/SMBus.
Technical Considerations
Transparent Bridging: Most I3C hubs maintain "software transparency," meaning the host controller sees all devices as if they were on a single bus, despite the physical cascading.
In-Band Interrupts (IBI): I3C hubs manage IBIs from downstream devices and pass them up the chain to the main controller, ensuring real-time responsiveness is maintained through the cascade.
Latency: While minimal, each level of cascading adds slight propagation delay that must be accounted for in time-sensitive applications.
Cascading I3C Hubs is designed to handle complex application scenarios. In the diagram above, we used a two-level cascading setup, connecting multiple Tower I3C Host Adapters via USB bus on the same computer. Each adapter then controls a different I3C Hub. This makes it easy to build automated test code to test different combinations and perform complex tests. We are only providing a schematic diagram of the test environment here; because specific chips may involve different control code logic, we haven't provided sample test code for now. Intel's official test cases include even more complex scenarios, such as three-level cascading, four-level cascading, and even more. Our Tower I3C Host Adapter can easily handle these scenarios using similar test environment setups.
Based on our Tower I3C Host Adapter, you can easily test the cascading functionality of I3C Hubs, meet complex testing needs, build automated testing environments, and shorten chip time-to-market. Because the topology of external chips connected to I3C Hubs is relatively complex, using multiple Tower I3C Host Adapters can accomplish these complex tests.
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