Single SRAM CPU Cache with Lookup Buffer for Area Reduction
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Solution Overview
Problem
The high cost and silicon area overhead of traditional two-memory cache systems, which use multiple SRAMs for cache and tag memory, make them expensive and resource-intensive, prompting the need for a more cost-effective solution that maintains performance.
Innovation Solution
A single shared SRAM is used, combining tag and data information, with a small lookup buffer to store recent cache line addresses, allowing for speculative reads and reducing the number of SRAMs required while maintaining performance comparable to two-way associative caches.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If traditional two-memory cache systems are used, then cache performance is improved, but hardware cost and silicon area increase
Solution Approach 1:
The patent combines tag memory and data memory into a single unified SRAM structure, eliminating the need for separate SRAM blocks. This merging reduces total silicon area while maintaining cache functionality through a single memory array that stores both tag and data information in an interleaved manner.
Solution Approach 2:
The single SRAM structure performs multiple functions simultaneously - storing both tag information and data information, handling both cache hit detection and data retrieval operations. This multi-functional design replaces the traditional separate tag memory and data memory structures, reducing overall hardware footprint.
2Speed
If traditional two-memory cache systems are used, then cache performance is improved, but hardware cost increases
Solution Approach 1:
The patent merges tag memory and data memory into a single SRAM block, reducing the total number of memory components required. This consolidation lowers hardware cost by eliminating redundant memory structures and reducing the overall bill of materials for the cache implementation.
Solution Approach 2:
The patent changes the organizational parameters of the SRAM from separate tag and data arrays to a unified structure with interleaved storage. This parameter change optimizes the memory layout to achieve both cost reduction and area efficiency while preserving cache performance characteristics.
3Area of stationary object
If a single SRAM is used for both tag and data, then hardware cost and area are reduced, but access complexity increases
Solution Approach 1:
The patent segments the single SRAM into distinct tag and data regions with clear boundary definitions. This segmentation allows the control logic to efficiently distinguish between tag access operations and data access operations, managing complexity through structured organization rather than monolithic design.
Solution Approach 2:
The patent introduces control logic that acts as an intermediary between the CPU and the unified SRAM structure. This mediator manages the complex interactions by translating CPU requests into appropriate SRAM access patterns, handling tag verification and data retrieval coordination to simplify the overall access interface.
Data Source
AI summary
One embodiment of the present invention relates to a CPU cache system that stores tag information and cached data in the same SRAM. The system includes an SRAM memory device, a lookup buffer, and a cache controller. The SRAM memory device includes a cache data section and a cache tag section. The cache data section includes data entries and the tag section includes tag entries associated with the data entries. The tag entries include memory addresses that correspond to the data entries. The lookup buffer includes lookup entries associated with at least a portion of the data entries. The number of lookup entries is less than the number of tag entries. The cache controller is configured to perform a speculative read of the cache data section and a cache check of the lookup buffer simultaneously or in a single cycle.