Configurable Tag Memory Power Management for Cache Efficiency
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Solution Overview
Problem
In cache memory systems, power is wasted due to the toggling and processing of unused higher-order bits in the tag field, which are not relevant for the actual system memory size, leading to inefficiencies in dynamic and leakage power consumption.
Innovation Solution
Implementing a tag memory with configurable and non-configurable tag columns, where the unused most significant bits are powered off during normal operation, using power switches controlled by a configuration circuit to conserve energy, and ensuring proper operation by disabling unnecessary comparisons for these bits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the cache memory uses a fixed tag field size based on maximum supported physical address, then the cache can support future memory expansions, but power is wasted due to toggling and processing of unused higher-order bits
Solution Approach 1:
The tag field is segmented into two distinct portions: a first portion corresponding to the maximum supported physical address size (e.g., 40 bits) and a second portion corresponding to the actual system memory address size (e.g., 32 bits). This segmentation allows the cache to maintain support for future memory expansions while selectively powering off unused higher-order bits to reduce power consumption.
Solution Approach 2:
The cache memory dynamically adjusts its operation based on the actual system memory configuration. Power switches are controlled to turn off unused tag bits during normal operation, and the comparison logic is dynamically configured to only compare relevant address bits, enabling the system to adapt between supporting maximum address space and actual memory size to optimize power usage.
2Reliability
If all tag bits are kept powered on to ensure full address space support, then the cache can handle any memory configuration, but dynamic and leakage power consumption increase
Solution Approach 1:
The tag field is divided into used and unused portions, allowing selective powering off of unused higher-order bits. This segmentation maintains reliability for actual memory operations while reducing leakage power by isolating and deactivating irrelevant circuitry.
Solution Approach 2:
Different portions of the tag field have different power states: the lower-order bits corresponding to actual memory addresses remain powered on and functional, while the higher-order bits that are not used are powered off. This local quality differentiation ensures reliability where needed while minimizing energy waste.
3Adaptability or versatility
If the cache memory is configured for maximum physical address size, then it can support larger future memory systems, but circuitry for deriving and processing unused signals consumes unnecessary power
Solution Approach 1:
The comparison logic is segmented to operate only on the second portion of the tag field corresponding to actual system memory addresses. This prevents unnecessary processing of unused higher-order bits, eliminating wasted processing power while maintaining the cache's ability to support future memory expansions through the preserved first portion of the tag field.
Solution Approach 2:
The unused higher-order tag bits and their associated processing logic are effectively extracted or isolated from the active comparison operation. Power switches control the inclusion of these bits in comparisons, allowing them to be taken out of the active circuit path during normal operation to eliminate processing power waste.
Data Source
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AI summary
In certain aspects, a tag memory (200) comprises a plurality of non- configurable tag columns (204) configured to be powered on during a normal operation; and a plurality of configurable tag columns (202), wherein a first portion of the plurality of configurable tag columns is configured to be powered off during the normal operation and a second portion of the plurality of configurable tag columns is configured to be powered on during the normal operation.