llvm / llvm/circt

Lower bi-directional bundles to interfaces

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#536 4 comments 0 reactions 0 assignees View on GitHub

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enhancement FIRRTL
Dominant language
C++
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Forks
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Avg merge
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Merged PRs (30d)
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Description

Support for lowering bundles to RTL structs was added in https://github.com/llvm/circt/pull/533. Structs cannot support bi-directional bundles, but SV interfaces can. Lowering bundles in this way was discussed a while back on Discourse: https://llvm.discourse.group/t/firrtl-aggregate-types-discussion/1806/17.

I propose to separate the lowering such that passive bundles always use structs, and use interfaces otherwise. It seems like the pieces for this are mostly in place already, and I'll start to take a look.

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First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

Research direction

Start by reviewing PR 533 and the linked Discourse discussion, then inspect the existing bundle-to-RTL-struct lowering. Done means passive bundles continue to lower to structs while bi-directional bundles lower to SystemVerilog interfaces.

Written by the indexing model from the issue text.

Assessment

Tech stack
cpp
Domain
compilers
Issue type
Feature
Difficulty
4/5
Estimated time
3-5 days
Activity status
Stale
Clarity
Mostly clear
Newbie friendliness
35/100

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