Refactor instruction retire and stepper #755
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The eventual goal here is to surface wait-states of the hart
(e.g. as caused by WFI and WRS.{NTO,STO}) into the stepper,
and handle debug triggers from execution for extensions such as
Sdtrig.
The refactor makes interrupt and exception handling more
symmetrical: both are now handled in the stepper.
This also removes the model-internal global instbits register
into a stepper-local variable, which fixes riscv#412.
This refactor is based on ideas discussed in riscv#398 and riscv#412.
Co-authored-by: Tim Hutt <timothy.hutt@codasip.com>
Co-authored-by: Jessica Clarke <jrtc27@jrtc27.com>
Co-authored-by: Alasdair Armstrong <alasdair.armstrong@cl.cam.ac.uk>
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The Wait state is exited on interrupts or if requested by the C emulator. The current implementation requests an immediate exit.
This adds an option to configure the maximum steps to remain in
the Wait state.
This is currently only used for WFI, but the basic mechanism can
be re-used for adding WRS.{STO, NTO} in the future.
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This is a slightly cleaner implementation of the draft proposed in #746.
The change now affects 33 files instead of 47 files, hopefully making it easier to review.
I added @Timmmm, @jrtc27 and @Alasdair as co-authors to the main commit as it's based on their discussions and suggestions in #398, #412 and #746.
If merged, I plan to port #398 to this design.