Draft docs/spec/fluidpop-isa.md ISA extension reference skeleton

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2026-05-25 19:41:05 -03:00

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Goal

Create the ISA extension reference skeleton at docs/spec/fluidpop-isa.md, listed as deliverable #3 in PLAN.md Section 10. The doc enumerates RoCC-routed instructions exposed by PopRoCCRouter to upstream Gemmini and any FluidPop-specific extensions, so RTL and software work share a single instruction inventory.

Sections to include:

Overview (RISC-V base + Gemmini RoCC + FluidPop additions)
Encoding conventions (RoCC opcode space, custom-0/1/2/3 usage — TODO)
Inherited Gemmini instructions (reference upstream Gemmini ISA doc; do not duplicate)
FluidPop-specific instructions (placeholder table: mnemonic / opcode / operands / semantics / status — all rows TBD)
Inter-chip communication hooks (any instructions that interact with PopLink fabric — TODO)
PHY/telemetry-visible CSRs (placeholder — defer to ADR finalization)
Privilege levels and trap behavior (TODO)
Open questions (which instructions truly need to be new vs reuse Gemmini's existing surface)

Acceptance criteria

docs/spec/fluidpop-isa.md exists with the sections above
Status: Draft skeleton + Owner: TBD header
Each section has TODO markers + 2-3 line intent
Instruction table is present with header row but rows are TBD placeholders
References upstream Gemmini ISA documentation rather than duplicating it
No fabricated opcodes or instruction semantics
Cross-references PLAN.md Sections 10, 8.2 (PopRoCCRouter) and the PopRoCCRouter Chisel skeleton issue

Plan refs

Section 10 (deliverable #3), Section 8.2 (PopRoCCRouter custom module)

Notes

Skeleton only — actual ISA decisions belong in dedicated ADRs to be filed once PopRoCCRouter design solidifies. Avoid committing to specific custom opcodes here; the doc's job is to provide structure and an open-questions list, not to specify the ISA.

## Goal Create the ISA extension reference skeleton at `docs/spec/fluidpop-isa.md`, listed as deliverable #3 in PLAN.md Section 10. The doc enumerates RoCC-routed instructions exposed by `PopRoCCRouter` to upstream Gemmini and any FluidPop-specific extensions, so RTL and software work share a single instruction inventory. Sections to include: - Overview (RISC-V base + Gemmini RoCC + FluidPop additions) - Encoding conventions (RoCC opcode space, custom-0/1/2/3 usage — TODO) - Inherited Gemmini instructions (reference upstream Gemmini ISA doc; do not duplicate) - FluidPop-specific instructions (placeholder table: mnemonic / opcode / operands / semantics / status — all rows TBD) - Inter-chip communication hooks (any instructions that interact with PopLink fabric — TODO) - PHY/telemetry-visible CSRs (placeholder — defer to ADR finalization) - Privilege levels and trap behavior (TODO) - Open questions (which instructions truly need to be new vs reuse Gemmini's existing surface) ## Acceptance criteria - [ ] `docs/spec/fluidpop-isa.md` exists with the sections above - [ ] `Status: Draft skeleton` + `Owner: TBD` header - [ ] Each section has `TODO` markers + 2-3 line intent - [ ] Instruction table is present with header row but rows are TBD placeholders - [ ] References upstream Gemmini ISA documentation rather than duplicating it - [ ] No fabricated opcodes or instruction semantics - [ ] Cross-references PLAN.md Sections 10, 8.2 (PopRoCCRouter) and the PopRoCCRouter Chisel skeleton issue ## Plan refs Section 10 (deliverable #3), Section 8.2 (PopRoCCRouter custom module) ## Notes Skeleton only — actual ISA decisions belong in dedicated ADRs to be filed once PopRoCCRouter design solidifies. Avoid committing to specific custom opcodes here; the doc's job is to provide structure and an open-questions list, not to specify the ISA.