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ywkang 687c98086d ADR housekeeping: category prefixes, lifecycle folders, retroactive 0034-0037

Filename + lifecycle:
- ADR rename to ADR-NNNN-<cat>-title.md with 8 3-letter category prefixes
  (dev / mem / lat / prog / algo / par / api / ver). Numbers stay immutable.
- ADR Lifecycle split into 3 folders, documented in CLAUDE.md Part 2:
  docs/adr/ (Accepted), docs/adr-proposed/ (Proposed/Stub/Draft),
  docs/adr-history/ (Superseded/Merged). Status field gains "Draft" for
  retroactive docs pending verification.

Merges (one ADR per topic, no change-history annotations):
- ADR-0017 absorbs ADR-0019 (Cube NOC + per-PE HBM connectivity, 10 D-items)
- ADR-0014 absorbs ADR-0021 (PE pipeline execution model, 8 D-items incl.
  TileToken self-routing and multi-op composite epilogue scope)
- ADR-0023 absorbs docs/ipcq-dma-codesign-hw.md as new "HW Realization
  Notes (Informative)" section (D16-D23 + Open HW Questions). codesign-hw.md
  deleted; ADR-0019/0021 moved to adr-history with one-line stub status

Retroactive documentation (G4 closures, code-verified):
- ADR-0037 forwarding component (TransitComponent: first-flit overhead,
  serial worker, path-based routing, single impl/multiple names)
- ADR-0036 IO_CPU component (target_start_ns global barrier stamping,
  per-cube fan-out, response aggregation)
- ADR-0035 M_CPU & M_CPU.DMA component (3 fan-out paths, DMA Resources,
  target_start_ns passthrough)
- ADR-0034 HBM controller internal design (per-PC state, address-based
  selection, flit-aware per-flit commit, async finalize, command-only
  fallback path)

Content updates:
- ADR-0010 expanded to full CLI surface (run/probe/web), retitled
  "Command Line Interface and Execution Semantics"
- ADR-0007 D2 rewritten to current state; ADR-0015 supersession notes pruned
- ADR-0005 wrapped in Decision header with D1-D5; ADR-0022 metadata
  block replaced with standard Status header
- ADR-0024 trimmed to rank=SIP launcher essentials (D1-D4);
  ADR-0027 cleaned of supersession history
- ADR-0033 D6 cleanup: address-based PC selection moved out of future-work
  (now documented in ADR-0034 D3); related D1/D3 wording realigned
- Cross-references back-filled in 5 ADRs (G3 gaps closed)

Onboarding docs split:
- docs/onboarding/ created
- moved: hw-architecture-overview.md, latency-model.md, di-presentation.md,
  ccl-author-guide{,.en}.md
- references updated in README, ADR-0023{,.en}, src/kernbench/ccl/__init__.py

Source / test / yaml: ADR-NNNN cross-references in docstrings and YAML
comments updated after the merges (ADR-0021->0014 D6, ADR-0019->0017 D8).
No behavior change.

Tooling:
- tools/verify_adr_lang_pairs.py + tests/test_verify_adr_lang_pairs.py
  (ADR EN/KO pair invariant checker)
- .claude/commands/report.md tracked (/report slash command)
- .gitignore: allow .claude/commands/*.md while keeping settings files ignored

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

2026-05-20 01:15:55 -07:00

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ADR-0004: Memory Semantics & Local-HBM Bandwidth Guarantee

Status

Accepted

Context

Accurately modeling PE↔HBM behavior is essential for kernel latency estimation. Each PE has a notion of “local HBM” that must guarantee full HBM bandwidth, independent of intervening on-die fabric bandwidth.

Decision

D1. Local HBM definition

Each PE is assigned a logically defined “local HBM” region.
Local HBM corresponds to the pseudo-channel subset directly attached to that PE’s router in the NOC mesh (ADR-0017 D4).
The path is: PE_DMA → local router → HBM_CTRL (switching overhead only, 0 mesh hops).
The mapping (HBM pseudo-channels → PE local regions) is derived from topology configuration.

D2. Local HBM bandwidth guarantee contract

Accesses from a PE to its local HBM MUST guarantee full effective HBM read/write bandwidth independent of intervening fabric bandwidth limits.
Effective HBM bandwidth = spec bandwidth x efficiency factor. The efficiency factor (configured via hbm_ctrl.attrs.efficiency, default 0.8) models real-world DRAM inefficiencies (refresh cycles, bank conflicts, page misses). For example: 256 GB/s spec x 0.8 = 204.8 GB/s effective.
The topology builder applies the efficiency factor to router-to-hbm edge bandwidth at graph construction time, so all downstream routing and latency computation uses the effective value.
This guarantee is modeled by:
- a dedicated logical path and/or service model that enforces HBM BW at the PE-local-HBM interaction point,
- while still incurring non-zero latency along explicitly modeled components.
HBM CTRL internal modeling (PC striping, cut-through, scheduling fidelity) is consolidated in ADR-0033 (Latency Model: Assumptions and Known Simplifications). The aggregate BW guarantee here remains the contract; ADR-0033 documents how the per-PC model realizes it and which scheduler effects are intentionally simplified.

D3. Remote PE HBM semantics (intra-cube)

A PE that accesses another PE's local HBM traverses the NOC:
- PE_DMA → NOC → (fabric hops) → target PE's NOC port → HBM_CTRL
NOC bandwidth and hop count may limit remote HBM access relative to local access.

D4. Non-local HBM semantics (inter-cube / inter-SIP)

Accesses from a PE to HBM in a different cube or SIP MAY be limited by:
- NOC bandwidth within the cube,
- inter-cube UCIe links,
- inter-SIP fabric (PCIe/UAL).
These paths MUST be explicit and traceable.

D5. Shared SRAM semantics

Each CUBE contains a shared SRAM accessible by all PEs in that CUBE.
Access path: PE_DMA → NOC → shared SRAM.
Shared SRAM bandwidth is limited by the NOC↔SRAM link bandwidth.
Shared SRAM is not part of the HBM address space; it is a separate memory domain.

Verification Notes

Tests should cover:

local-HBM case: BW matches HBM BW regardless of fabric BW parameter
remote PE HBM case: latency includes mesh hop traversal
non-local cases (inter-cube/inter-SIP): BW/latency respond to fabric/link parameters
shared SRAM case: access via NOC with correct BW

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