N2 Full Mesh AXI Bus Fabric Reduces Signal Lines
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Solution Overview
Problem
The existing AXI bus built using crossbar fabric has a large number of signal lines, making wiring challenging on the chip, leading to increased latency, reduced bus frequency, and difficulty in access and extension, along with routing congestion due to its single routing structure.
Innovation Solution
An AXI bus based on an N2 full Mesh fabric using 2×2 AXI crossbars as basic units, which reduces the number of signal lines, enhances scalability, and provides a flexible routing mechanism to prevent congestion and share bandwidth during heavy data traffic.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If crossbar fabric is used to build AXI bus, then connectivity between master and slave devices is achieved, but the number of signal lines increases quadratically
Solution Approach 1:
The patent divides the large-scale crossbar fabric into multiple smaller 2×2 crossbar sub-fabrics organized in a mesh topology. Each sub-fabric handles local connectivity, while inter-subfabric connections provide long-distance routing. This segmentation reduces the signal line count from O(N²) in a monolithic crossbar to O(N) in the mesh structure, as each node only needs to connect to its immediate neighbors rather than all other nodes.
Solution Approach 2:
The patent transitions from a two-dimensional crossbar matrix to a multi-dimensional mesh network. By organizing crossbars in a hierarchical mesh structure with multiple levels and dimensions, the system achieves scalable connectivity without quadratic growth in signal lines. The mesh topology adds spatial dimensions for routing, allowing data to travel through intermediate nodes rather than requiring direct point-to-point connections.
2Adaptability or versatility
If the number of ports is increased linearly, then the AXI bus can support more devices, but the number of signal lines increases quadratically
Solution Approach 1:
The patent segments the bus system into multiple 2×2 crossbar units arranged in a mesh, where each unit serves a local group of devices. This allows linear scaling of device support while keeping each crossbar unit's complexity constant. The overall system complexity grows linearly with the number of units rather than quadratically with the total number of devices.
Solution Approach 2:
Each 2×2 crossbar unit serves multiple functions: local device connectivity, intermediate routing node, and part of the larger mesh network. This multi-functionality allows the same basic building block to scale the system from small to large configurations without increasing per-unit complexity, enabling linear device scaling with linear complexity growth.
3Adaptability or versatility
If crossbar fabric with many signal lines is used, then comprehensive device connectivity is achieved, but wiring becomes difficult to implement on chip
Solution Approach 1:
The patent divides the connectivity function across multiple small 2×2 crossbar units rather than one large crossbar. Each unit has simple, localized wiring connections that are easy to implement physically on the chip. The segmented approach transforms a single complex wiring challenge into multiple simple wiring tasks, significantly improving manufacturability while maintaining comprehensive connectivity through the mesh interconnection.
4Adaptability or versatility
If signal lines are made very long to connect all ports, then complete connectivity is achieved, but latency increases and bus frequency is reduced
Solution Approach 1:
The patent uses a mesh topology that provides multiple dimensional paths for data transmission. Instead of requiring long direct connections across the entire chip, data can travel through intermediate nodes in a multi-hop fashion. This dimensional approach to routing reduces the effective transmission distance and allows for optimized local interconnections, improving signal speed and reducing latency while maintaining full connectivity.
5Device complexity
If single routing structure is used, then routing is simplified, but routing congestion occurs easily
Solution Approach 1:
The patent segments the routing function across multiple independent 2×2 crossbar units in a mesh. This segmentation creates multiple parallel routing paths through different nodes and links. When congestion occurs on one path, data can be routed through alternative paths, improving reliability and congestion resistance while keeping individual routing decisions simple at each node.
Solution Approach 2:
The mesh routing structure enables dynamic path selection at each node based on current network conditions. Each crossbar unit can independently choose different output ports based on destination and current link availability, creating adaptive routing that responds to congestion in real-time. This dynamic behavior improves reliability without requiring complex centralized control.
Data Source
AI summary
An advanced extensible interface (AXI) bus is disclosed. 2×2 AXI crossbars are used as basic units; each including two slave interfaces and two master interfaces; an N2 full Mesh fabric is built by using the basic units, so that each slave interface on one basic unit is connected to a master interface on another basic unit to form a first path. A data transmission method includes: receiving, through a master interface of a basic unit, a data packet sent by a master device; sending, through a slave interface of the basic unit, the data packet to a destination slave device by using an AXI bus; receiving, through the slave interface of the basic unit, a response packet returned by the destination slave device, where the basic units are 2×2 AXI crossbars and the AXI bus is based on an N2 full mesh fabric built by using the basic units.