Add FFT testbench

[n0thingNoob]

Summary\n- Add an FFT testbench that validates Zeonica shared-memory output against a source-level CPU golden model.\n- Update the Zeonica_Testbench submodule pointer to the FFT generated artifacts commit.\n- Skip the FFT test in clean CI checkouts when the submodule artifact is unavailable.\n\n## Validation\n- go test -count=1 ./test/testbench/fft\n- golangci-lint run --timeout=10m ./test/testbench/fft

[Copilot]

Pull request overview

Adds a new FFT testbench harness and a Tenstorrent-inspired dataflow case-study demo, while extending Zeonica’s emulator/driver stack with a new TT_MATMUL_TILE_U32 opcode and host-side per-core data token injection/collection APIs.

Changes:

• Introduce a 256-point FFT testbench (runtime config, harness, and Go test) that validates shared-memory behavior against a source-level integer FFT model.
• Add a TT-Metalium-inspired multicore matmul + eltwise-add experimental case study (docs, kernels, demo harness, optional trace-summary output).
• Extend core/emulator + driver + tile interfaces to support TT_MATMUL_TILE_U32 and host drain/inject of cgra.Data tokens.

Reviewed changes

Copilot reviewed 34 out of 35 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
test/testbench/fft/main.go	FFT harness: loads YAML program, preloads shared memory, runs, and checks results vs CPU model.
test/testbench/fft/fft_test.go	Go test wrapper around the FFT harness.
test/testbench/fft/arch_spec.yaml	Arch spec for FFT testbench (shared-memory mode + trace logging).
experiments/tenstorrent_dataflow_case_study/tt_metal_sources/README.md	Doc placeholder for TT-Metal source notes policy.
experiments/tenstorrent_dataflow_case_study/tt_metal_sources/matmul_multicore_source_note.md	Extracted dataflow pattern notes for TT multicore matmul (no vendored source).
experiments/tenstorrent_dataflow_case_study/TODO.md	Case-study TODO/status tracking.
experiments/tenstorrent_dataflow_case_study/results/summary.md	Summary of the case study’s supported/unsupported claims + current result.
experiments/tenstorrent_dataflow_case_study/results/README.md	Results directory placeholder.
experiments/tenstorrent_dataflow_case_study/results/matmul_multicore_trace_summary.md	Example/record of lightweight lifecycle trace summary output.
experiments/tenstorrent_dataflow_case_study/README.md	Case study overview, scope, and reproduction command.
experiments/tenstorrent_dataflow_case_study/matmul_multicore_demo/main.go	Multicore matmul demo using TT_MATMUL_TILE_U32 and per-core token feed/collect.
experiments/tenstorrent_dataflow_case_study/lowering_notes/README.md	Lowering-notes directory placeholder.
experiments/tenstorrent_dataflow_case_study/lowering_notes/matmul_multicore_dataflow_mapping.md	Manual lowering boundary + mapping rules for the matmul demo.
experiments/tenstorrent_dataflow_case_study/kernels/matmul_2x2/README.md	Kernel artifact documentation for the full-size multicore matmul demo.
experiments/tenstorrent_dataflow_case_study/kernels/matmul_2x2/matmul_multicore.yaml	4x4 per-PE YAML program invoking TT_MATMUL_TILE_U32.
experiments/tenstorrent_dataflow_case_study/kernels/eltwise_add/README.md	Documentation for minimal eltwise-add producer/consumer demo.
experiments/tenstorrent_dataflow_case_study/kernels/eltwise_add/eltwise_add.yaml	1x1 YAML program for ADD West/North -> East.
experiments/tenstorrent_dataflow_case_study/figures/README.md	Figures directory placeholder + policy.
experiments/tenstorrent_dataflow_case_study/figures/matmul_multicore_visuals.md	Mermaid figure sources + visual tables for the case study.
experiments/tenstorrent_dataflow_case_study/eltwise_add_demo/main.go	Minimal demo harness for eltwise-add kernel.
experiments/tenstorrent_dataflow_case_study/DESIGN.md	Design + fidelity boundary + evidence chain for the case study.
experiments/tenstorrent_dataflow_case_study/configs/README.md	Configs directory placeholder.
experiments/tenstorrent_dataflow_case_study/CLAIM_BOUNDARY.md	Explicit claim boundary (what’s supported vs what must not be claimed).
experiments/tenstorrent_dataflow_case_study/CASE_STUDY_TEXT.md	Draft paper-ready case-study narrative.
core/tt_matmul_tile_test.go	Unit tests for ttMatmulTileU32 (single ktile, 2 ktiles, kt=20 shape).
core/opcodes.go	Register TT_MATMUL_TILE_U32 as a vector opcode (plus formatting updates).
core/emu.go	Implement TT_MATMUL_TILE_U32 and add host-drain tracking; modifies PHI_START behavior.
core/core.go	Add host inject/drain methods and skip network send on host-drained directions.
core/builder.go	Initialize HostDrainDirections in core state.
config/platform.go	Plumb new tile APIs through platform tile wrapper.
cgra/cgra.go	Extend cgra.Tile interface with inject/drain/host-drain controls.
api/mock_cgra_test.go	Update gomock tile mock for new tile methods.
api/driver.go	Add per-core cgra.Data feed/collect tasks and APIs.
api/data_token_test.go	Test that per-core feed/collect carries a vector token end-to-end.

Files not reviewed (1)

• api/mock_cgra_test.go: Language not supported

Comments suppressed due to low confidence (1)

core/emu.go:3493

• runPhiStart currently allows both source predicates to be true, in which case it will silently prefer src1 and ignore src2. This breaks the mutual-exclusion invariant enforced by runPhi and can hide control-flow bugs by producing non-deterministic/incorrect PHI selection instead of failing fast.

		src2Struct := i.readOperand(src2, state) // only in normal path will consume src2
		src2Val := src2Struct.First()
		src2Pred := src2Struct.Pred
		if src1Pred {
			result = src1Val
			finalPred = src1Pred
		} else { // src2Pred is true or both are false(arbitrary)
			result = src2Val
			finalPred = src2Pred
		}

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