Lambda — LonghornSilicon decode-attention accelerator (monorepo)

Lambda is the LonghornSilicon LLM decode-attention accelerator. This is the monorepo: one clone, atomic cross-block commits, one CI. Each functional block is a self-contained folder under src/blocks/<block>/ (sw/ rtl/ pdk/ docs/ research/); cross-block integration lives in chip/; the architecture spec / ISA is the standalone lambda-arch repo; Cadence chamber tooling is in tools/. Each block auto-mirrors to a read-only lambda-<block> repo so it keeps its own browsable/cloneable URL.

Branch model — main is a clean scaffold; RTL lives on rev0. main carries structure, docs, pdk/ configs, Python reference-models (the golden spec), tooling, and the proven results/ record — but no .sv/.v RTL. RTL is developed on the rev0 revision branch (PR into rev0; a lead blesses → merges to main). Longhorn Silicon is a talent-development tapeout — students and leads write the RTL. To see/work on RTL: git checkout rev0. Full model: docs/REVISION_SYNC_SOP.md §6a.

Targets — one RTL, multiple PDKs. The product target is TSMC 16nm (N16FFC) — under NDA, so we prove/estimate on open PDKs. GF180MCU is the near-term chipathon shuttle (SSCS Chipathon 2026 — a real open-silicon tapeout of the decode attention datapath Q·Kᵀ → softmax → P·V + KVE + TIU + ACU gate); Sky130 is the flagship dev proof; ASAP7 (7nm FinFET) is the research bracket closest to 16nm. GF180/Sky130 are proxies, not the destination — the 16nm hardening is a separate private overlay pointing at this same RTL. See AGENTS.md for the full targets note.

New here? Read AGENTS.md first (front door + runbook + lab-notebook rules), then DECISIONS.md and docs/.

Layout

Restructured 2026-07 to the src/blocks/ taxonomy (adopted from the architecture repo) — one clean, legible map of every block including the not-yet-built ones. See docs/REORG_NOTES.md.

lambda/
├── src/
│   ├── blocks/
│   │   ├── acu/        Attention Compute Unit umbrella → mirror lambda-acu
│   │   │   ├── mate/               Q·Kᵀ + P·V matmul PEs         → mirror lambda-mate
│   │   │   ├── vecu/               decode online-softmax/RoPE/RMSNorm → mirror lambda-vecu
│   │   │   └── precision_controller/ INT8/FP16 per-tile gate     → mirror lambda-precision-controller
│   │   ├── kve/        KV Cache Engine — ChannelQuant codec       → mirror lambda-kve
│   │   ├── tiu/        Token Importance Unit — H2O keep/demote/evict → mirror lambda-tiu
│   │   ├── msc/        Memory Subsystem Controller   (spec-only stub)
│   │   ├── lsu/        Layer Sequencer               (spec-only stub)
│   │   └── hif/        Host Interface (PCIe Gen3 x1) (spec-only stub)
│   ├── isa/            Chip-level ISA (LSU opcodes, CSR map); per-block ISA lives in each block
│   └── golden/         Chip-level golden reference + index of per-block reference models
├── chip/     Cross-block integration: verif/ (tb_chip_cosim) + pdk/gf180/ (full-chip padring assembly)
├── tools/    Cadence-chamber launcher framework (reconciled from the architecture repo)
├── tests/integration/  Cross-block cosim + end-to-end decode traces
├── docs/     Chip-wide: STATUS, REVISION_SYNC_SOP, REVISIONS, ROADMAP, PROGRESS (generated),
│             documentation_standard, audits, dataflow_walkthrough, paper/.
├── research/ Chip-wide research (APA RL project + chip-wide exploration).
├── scripts/  Revision-Sync tooling (gen_progress, check_block_structure, cut_revision, rtl_doc_gate).
├── arch.yml  Machine-readable architecture (blocks, tiles, dataflow).
└── .github/workflows/mirror-blocks.yml  Auto-mirror each src/blocks/<block> to its standalone repo.

Blocks

Each block folder is self-contained and auto-mirrors to a standalone read-only lambda-<block> repo.

Block	Folder	Mirror repo
KV Cache Engine (ChannelQuant codec)	src/blocks/kve/	lambda-kve
Token Importance Unit (H2O keep/demote/evict)	src/blocks/tiu/	lambda-tiu
Attention Compute Unit (umbrella)	src/blocks/acu/	lambda-acu
├ MatE — Q·Kᵀ + P·V matmul PEs	src/blocks/acu/mate/	lambda-mate
├ VecU — decode online-softmax	src/blocks/acu/vecu/	lambda-vecu
└ Precision Controller — INT8/FP16 gate	src/blocks/acu/precision_controller/	lambda-precision-controller
Memory Subsystem Controller	src/blocks/msc/ (spec-only stub)	—
Layer Sequencer	src/blocks/lsu/ (spec-only stub)	—
Host Interface (PCIe Gen3 x1)	src/blocks/hif/ (spec-only stub)	—

Cross-block integration (cosim + full-chip PDK) lives in chip/; chip-wide docs in docs/; chip-wide research in research/.

Auto-mirror

On every push to main and rev0, .github/workflows/mirror-blocks.yml runs git subtree split --prefix=src/blocks/<block> and force-pushes each block to the same-named branch of its standalone read-only mirror — so each mirror has a main (scaffold) and a rev0 (RTL):

monorepo path	mirror repo	status
src/blocks/kve	LonghornSilicon/lambda-kve	active
src/blocks/tiu	LonghornSilicon/lambda-tiu	active
src/blocks/acu	LonghornSilicon/lambda-acu	active (umbrella)
src/blocks/acu/mate	LonghornSilicon/lambda-mate	active
src/blocks/acu/vecu	LonghornSilicon/lambda-vecu	active
src/blocks/acu/precision_controller	LonghornSilicon/lambda-precision-controller	active

Mirrors are read-only — open PRs against this monorepo; they propagate out on the next push.

Auto-mirror is live — the workflow uses the configured MIRROR_PAT repo secret to push each block to its mirror on every commit to main. No setup needed.

Known gotchas (chip-wide) — check before debugging

Environment / flow

• LHS box venv is read-only, no numpy/pip. Use /home/shadeform/cuda_advisor/.venv/bin/python for numpy; reinstall iverilog/yosys each session. Prefer pure-Python golden generators.
• ORFS ASAP7 is 4×-drawn. Areas read 16× too large unless de-scaled — confirm the SITE size (0.054×0.270) before quoting µm².

GF180 hardening

• DESIGN_REPAIR_MAX_SLEW_PCT=0 DISABLES slew repair (it passes -slew_margin 0) — an inverted setting. Restore ~20% or you get thousands of false max-slew/cap violations.
• LibreLane escaped-identifier instance naming takes 3 different forms across PDN_MACRO_CONNECTIONS regex / instances placement / YAML quoting — match each exactly.

Block-specific gotchas live in each block's README.md (kve/README.md, tiu/README.md).

License / contributing

Develop in this monorepo. The lambda-<block> repos are read-only mirrors — do not push to them.