Hierarchical Branch Prediction Using Micro-BTB Enablement

The patent divides the branch prediction system into two segments: a small micro-BTB for low-power operation and a large main-BTB for high-performance operation. The micro-BTB handles common branch prediction tasks with minimal energy consumption, while the main-BTB provides comprehensive coverage when needed. This segmentation resolves the contradiction by allowing the system to achieve adequate prediction coverage through the small micro-BTB most of the time, avoiding the continuous energy cost of the large main-BTB.

The patent implements dynamic switching between micro-BTB and main-BTB based on runtime conditions such as branch prediction accuracy requirements and power state. An enablement circuit dynamically activates the main-BTB only when the micro-BTB fails to provide accurate predictions or when performance requirements demand it. This dynamic approach resolves the contradiction by adapting the prediction coverage to actual needs rather than maintaining constant high coverage at high energy cost.

The patent merges the micro-BTB and main-BTB into a unified hierarchical system where both structures coexist and work together. The micro-BTB operates as the primary predictor for energy efficiency, while the main-BTB serves as a backup for accuracy-critical cases. This merging resolves the contradiction by combining the energy efficiency of the small micro-BTB with the accuracy assurance of the large main-BTB, achieving both goals simultaneously rather than forcing a trade-off.

The patent introduces an enablement circuit and confidence counter as intermediary components that mediate between the micro-BTB and main-BTB. These intermediaries monitor the micro-BTB's prediction accuracy and dynamically enable the main-BTB when prediction confidence is low or misprediction rate is high. This intermediary mechanism resolves the contradiction by automatically compensating for the micro-BTB's limited accuracy with the main-BTB's comprehensive coverage only when necessary, maintaining energy efficiency while ensuring prediction accuracy.

The patent segments the prediction capability into two levels: basic prediction handled by the simple micro-BTB and advanced prediction handled by the main-BTB. The micro-BTB implements only essential branch prediction functions with minimal structure, while the main-BTB provides sophisticated prediction capabilities when activated. This segmentation resolves the contradiction by delivering adequate prediction capability through the simple micro-BTB most of the time, avoiding the complexity overhead of the advanced main-BTB structure.

The patent implements dynamic control of the main-BTB activation through an enablement circuit that responds to runtime conditions such as misprediction rate and confidence counter values. The complex main-BTB structure remains inactive by default, reducing effective device complexity, and is activated only when prediction capability requirements exceed what the micro-BTB can provide. This dynamic approach resolves the contradiction by adapting the effective complexity to actual prediction needs rather than maintaining constant high capability at constant complexity cost.