Checkpoint Circuitry for Long Latency Instruction Recovery

The patent applies local quality by differentiating checkpoint storage based on instruction type. Instead of uniform frequent checkpointing, it selectively stores checkpoints only for long-latency instructions (like floating-point divide instructions) that are likely to be interrupted, while skipping short-latency instructions. This localized approach reduces overall checkpoint storage overhead while maintaining adequate rewind capability for critical instructions.

The patent changes the parameter of checkpoint frequency based on instruction characteristics. It dynamically determines whether to store a checkpoint by evaluating the expected completion latency of each instruction. For instructions with latency exceeding a threshold (e.g., floating-point divide), checkpoints are stored; for others, they are not. This parameter-based differentiation optimizes the balance between rewind distance and storage overhead.

The patent applies preliminary action by storing checkpoint information before long-latency instructions complete execution. When an interrupt occurs during a long-latency instruction, the system can immediately restore from the pre-stored checkpoint and resume execution, rather than waiting for the instruction to complete. This preliminary checkpointing enables fast interrupt response while maintaining execution integrity through proper state restoration.

The patent extracts the checkpointing function from the normal instruction completion flow. Instead of requiring instruction completion as a prerequisite for interrupt handling, it separates checkpoint storage from instruction completion, allowing interrupts to be handled independently. The checkpoint information is stored in advance and can be utilized immediately upon interrupt occurrence, decoupling interrupt response from instruction completion timing.