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Load Store Queue: LSQ

Submodule List

Submodule Descrption
VirtualLoadQueue TODO
LoadQueueRAR TODO
LoadQueueRAW TODO
LoadQueueReplay DONE
LoadQueueUncache TODO
LoadExceptionBuffer TODO
StoreQueue DONE

Functional Description

The LSQ consists of two parts, LoadQueue and StoreQueue, with a wrapper layer for convenient port connections. The primary function of Lsqwrapper is just wiring.

  • LoadQueue

    • LoadQueueRAR: RAR violation check queue

    • LoadQueueRAW: RAW violation check queue

    • LoadQueueUncache: MMIO/Noncacheable load instruction processing queue

    • LoadQueueReplay: Load instruction scheduling replay queue

    • LoadExceptionBuffer: Exception handling queue for Load instructions

    • VirtualLoadQueue: Sequential maintenance queue for Load instructions

  • StoreQueue

Feature 1: Update LqPtr for Load instructions and SqPtr for Store instructions

  • Due to timing considerations, the allocation of LqPtr and SqPtr is split into two parts, as shown in the figure

LSQ allocation

  • Dispatch stage

    • Count the number of LoadFlow or StoreFlow for each instruction and calculate the LqPtr or SqPtr in a cumulative manner

  • LSQ enqueue phase

    • Accurately calculate LqPtr or SqPtr by accumulating based on the enqPtr maintained by LoadQueue or StoreQueue

  • LsqEnqCtrl update logic

    • If a pipeline flush occurs, update based on the number of flushed Load or Store instructions and the commit count

    • If no pipeline flush occurs but there is an allocation request, update based on the enqueue and commit counts

    • Otherwise, update based on the commit count

Overall Block Diagram

Overall LSQ Framework

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Interface timing

Timing example of Load and Store instruction enqueue interface

Enqueue Update
{#fig:LSQ-LsqEnqCtrl-Timing width=90%}