revert(lpc): remove LPC804 from SPI+DMA driver gate — LPC804 has no DMA silicon

[zackees]

Reverts the FastLED-side of the phantom LPC804 DMA cascade (PRs #3500 + #3505). LPC804 silicon has no DMA peripheral.

Empirical evidence (per agents/docs/peripheral-existence.md)

Four independent signals from NXP's own sources all agree LPC804 has no DMA:

Signal	LPC845	LPC804
mcux-sdk/devices/<CHIP>/<CHIP>.h grep count of DMA_Type	2	0
<CHIP>_BASE macro for DMA0	present (0x50008000)	absent
FSL_FEATURE_SOC_DMA_COUNT in <CHIP>_features.h	1	absent
fsl_inputmux_connections.h in devices/<CHIP>/drivers/	present	absent

LPC804 also has no dedicated DMA chapter in UM11065 — the 3 DMA hits in the whole 700+ page manual are all copy-paste leftovers in ADC / DAC / CAPT / I2C / SPI comment blocks referring to "DMA trigger flags" for a peripheral that does not exist on this die. Address 0x50008000 is a reserved AHB slot on LPC804.

Diagnosis credit @phatpaul in #3499 comment 4855252061. The revert follows the guardrail landed in #3506 / #3507 (agents/docs/peripheral-existence.md), which now automates the exact grep recipe that would have caught the fabrication before it shipped.

Changes

• src/platforms/arm/lpc/spi_arm_lpc_dma.h — narrow build gate back to FL_IS_ARM_LPC_845 only. Add a compile-time #error that fires with a clear "LPC804 has no DMA" diagnostic + link to peripheral-existence guardrail if a user tries to opt into FASTLED_LPC_SPI_DMA on LPC804. Delete the earlier "LPC804 vendor CMSIS PAL prerequisite" text and the LPC804-specific FASTLED_LPC_SPI_DMA_CHANNEL default (0 → dropped; the LPC845 default of 4 stands).
• examples/AutoResearch/AutoResearchSpiDma.h — narrow harness gate back to LPC845 only.
• examples/AutoResearch/AutoResearchLowMemory.h — narrow include + bind gates back to LPC845 only.
• ci/autoresearch/phases.py — collapse LPC_DMA_SPI_ENVS back to LPC_WS2812_ENVS (LPC845 environments only). Drop the is_lpc804 → core_hz = 15_000_000 branch (always 24 MHz now).
• ci/autoresearch/args.py — update --dma-spi --help text: drop LPC804 mention + fbuild prerequisite; note LPC804 not supported.
• src/platforms/arm/lpc/README.md — LPC804 row now clearly documents "no DMA-async SPI" with citation to the guardrail. spi_arm_lpc_dma.h files entry marked LPC845-only. Feature-defines section corrected. References/Shipped entry for feat(lpc): widen spi_arm_lpc_dma.h gate to include LPC804 (#3499) #3500 strikethrough-annotated with "REVERTED — see peripheral-existence.md."

Follow-up (out of scope for this PR)

• Revert framework-arduino-lpc8xx#35 (the fabricated DMA_Type in variants/lpc804/LPC804.h).
• Revert or supersede fbuild#916 (bumped ArduinoCore-LPC8xx pin for the fabricated typedef).
• Close FastLED LPC804 SPI DMA support blocked on vendor CMSIS PAL — missing DMA_Type / DMA0 in <LPC804.h> #3499 as INVALID.

Verification

• bash compile wasm --examples AutoResearch — clean
• bash lint — python_pipeline passes; cpp_linting fails only on the same pre-existing Rust-binary silent-fail this Windows environment has (unrelated to this diff; see fix(lint): stream Rust build stdout/stderr + replace deprecated os.system in ci/ #3510)

Test plan

• Grep confirms zero LPC804 references remain in spi_arm_lpc_dma.h gate (only in documentation explaining why it's not supported)
• Grep confirms zero LPC804 references in AutoResearchSpiDma.h / AutoResearchLowMemory.h gates
• LPC_DMA_SPI_ENVS == LPC_WS2812_ENVS in phases.py
• Follow-up PR for framework-arduino-lpc8xx#35 revert

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

Generated with Claude Code

Summary by CodeRabbit

• Bug Fixes

  • Clarified that DMA-based SPI support is available only on LPC845 boards, and LPC804 now shows a clear unsupported message.
  • Improved build-time checks so invalid board/configuration combinations fail earlier with more direct guidance.

• Documentation

  • Updated help text, examples, and platform docs to match the current supported hardware and default DMA channel guidance.

[coderabbitai]

Caution

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📥 Commits

Reviewing files that changed from the base of the PR and between 8d69069 and 5c13e20.

📒 Files selected for processing (6)

• ci/autoresearch/args.py
• ci/autoresearch/phases.py
• examples/AutoResearch/AutoResearchLowMemory.h
• examples/AutoResearch/AutoResearchSpiDma.h
• src/platforms/arm/lpc/README.md
• src/platforms/arm/lpc/spi_arm_lpc_dma.h

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📝 Walkthrough

Walkthrough

This PR reverts prior LPC804 SPI+DMA support, restricting FASTLED_LPC_SPI_DMA compilation to LPC845 only. Changes span the core driver header, AutoResearch example harnesses, CI autoresearch scripts/args, and README documentation, adding an explicit compile-time error for LPC804 usage.

Changes

LPC845-only SPI+DMA gating revert

Layer / File(s)	Summary
Core driver gating and diagnostics src/platforms/arm/lpc/spi_arm_lpc_dma.h	Preprocessor gating requires FL_IS_ARM_LPC_845; a new #error triggers on LPC804 + FASTLED_LPC_SPI_DMA; documentation, resource notes, and class brief updated to LPC845-only.
AutoResearch example gating examples/AutoResearch/AutoResearchLowMemory.h, examples/AutoResearch/AutoResearchSpiDma.h	Combined LPC845/LPC804 preprocessor conditions replaced with LPC845-only guards; comments updated to state LPC804 lacks DMA.
CI autoresearch harness and args update ci/autoresearch/phases.py, ci/autoresearch/args.py	LPC_DMA_SPI_ENVS narrowed to LPC845; --dma-spi dispatcher rejects LPC804 with updated message; bench clock/channel logic fixed to LPC845; help text updated.
README documentation update src/platforms/arm/lpc/README.md	Supported platforms table, spi_arm_lpc_dma.h entry, feature defines, and shipped history updated to reflect LPC845-only support and the reverted gate-widening attempt.

Estimated code review effort: 2 (Simple) | ~15 minutes

Sequence Diagram(s)

sequenceDiagram
participant User
participant ArgsPy as args.py
participant PhasesPy as phases.py
participant Bench as _run_lpc_dma_spi_tests
User->>ArgsPy: pass --dma-spi flag
ArgsPy->>PhasesPy: parsed args with dma_spi=true
PhasesPy->>PhasesPy: check env in LPC_DMA_SPI_ENVS
PhasesPy-->>User: reject if LPC804 (no DMA peripheral)
PhasesPy->>Bench: run bench for LPC845 env
Bench-->>User: print LPC845 clock/channel defaults

Loading

Possibly related issues

• LPC804 SPI DMA support blocked on vendor CMSIS PAL — missing DMA_Type / DMA0 in <LPC804.h> #3499: Touches the same LPC804/LPC845 DMA gate in spi_arm_lpc_dma.h, and this PR reverses the direction of that change back to LPC845-only.

Possibly related PRs

• FastLED/FastLED#3500: This PR directly reverts the gate widening to LPC804 introduced there, restoring LPC845-only compilation with a new #error.
• FastLED/FastLED#3502: This PR amends the SPI+DMA README documentation added there to state LPC845-only support and LPC804's compile-time error.
• FastLED/FastLED#3503: Both PRs modify the same --dma-spi CI flow across ci/autoresearch/args.py, ci/autoresearch/phases.py, and the AutoResearch example headers.

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch revert/lpc804-phantom-dma-cascade

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