Silicon Photonic Waveguides for Off-Chip Cache Access
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Solution Overview
Problem
Existing cache designs face limitations in space and wire delays, leading to non-uniform access times and insufficient bandwidth for high-speed cache access, particularly in single-chip processor designs and off-chip electronic connections.
Innovation Solution
The use of silicon photonic waveguides to directly connect processor chips to individual cache banks on a separate cache chip, enabling optical communication and overcoming wire delays and bandwidth limitations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If large caches are placed on a separate chip, then area limitations are reduced, but off-chip electronic connections do not provide sufficient bandwidth for high-speed cache access
Solution Approach 1:
The patent replaces electronic inter-chip connections with optical waveguide connections. The processor chip and cache chip are connected via silicon photonic waveguides that transmit optical signals, enabling high-speed cache access while maintaining separate chip architecture for large cache capacity.
2Quantity of substance
If large caches are implemented in single-chip processor designs, then cache capacity increases, but wire delays cause non-uniform access times and require optimized wires that consume more area
Solution Approach 1:
The patent divides the cache into multiple cache banks (e.g., eight cache banks) that are independently accessible via separate optical waveguides. This segmentation allows each cache bank to be accessed with uniform low latency through dedicated optical channels, eliminating the wire delay problems of monolithic on-chip caches.
Solution Approach 2:
The patent substitutes electronic wire connections with optical waveguide connections for cache access. The silicon photonic waveguides transmit optical signals from the processor chip to each cache bank, providing uniformly low-latency access across all cache banks regardless of their physical location on the chip.
3Loss of time
If optimized wires are used to reduce wire delays, then access time improves, but area consumption increases and routing complexity increases
Solution Approach 1:
The patent replaces complex electronic wire routing with a regular array of silicon photonic waveguides. The waveguides are arranged in a systematic pattern that connects processor chip structures to cache banks, providing uniform low-latency access without the routing complexity of optimized electronic wires.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach allows for a large cache with uniformly low-latency access times, eliminating area tradeoffs and communication penalties, thereby significantly improving performance by providing high-bandwidth, low-latency connections.
Implementation Method 1
a silicon photonic waveguide is comprised of waveguides in the processor chip, the communications substrate, and the cache chip, and forms an optical channel that routes an optical signal directly from the structure to a cache bank in the cache chip
Implementation Method 2
the silicon photonic waveguide forms an optical channel that routes an optical signal directly from the structure to a cache bank in the cache chip via the communications substrate
Data Source
AI summary
The disclosed embodiments provide a system in which a processor chip accesses an off-chip cache via silicon photonic waveguides. The system includes a processor chip and a cache chip that are both coupled to a communications substrate. The cache chip comprises one or more cache banks that receive cache requests from a structure in the processor chip optically via a silicon photonic waveguide. More specifically, the silicon photonic waveguide is comprised of waveguides in the processor chip, the communications substrate, and the cache chip, and forms an optical channel that routes an optical signal directly from the structure to a cache bank in the cache chip via the communications substrate. Transmitting optical signals from the processor chip directly to cache banks on the cache chip facilitates reducing the wire latency of cache accesses and allowing each cache bank on the cache chip to be accessed with uniform latency.