feat(startup): named weak IRQ handlers for LPC845/LPC804 vector slots

[zackees]

Summary

Standard CMSIS startup pattern: every chip-level vector slot gets a peripheral-named handler (SPI0_IRQHandler, DMA0_IRQHandler, USART1_IRQHandler, ...) weak-aliased to Default_Handler, so a sketch or library installs an ISR by simply defining the strong symbol.

Why

All 32 chip IRQ slots previously pointed at Default_Handler directly — no way to hook any peripheral interrupt from user code. That blocks ISR-driven drivers entirely: FastLED's next LPC845 work (ISR-refillable SPI-DMA streaming, async UART TX with DMA chunk refill — FastLED/FastLED#3453 follow-up) needs DMA0_IRQHandler. The Cortex-M0+ has no VTOR, so the only alternative is a RAM vector table via SYSMEMREMAP plus a reserved block at the start of SRAM in every linker script — far more invasive.

Scope

• LPC845 + LPC804: full named maps per each chip's vendor CMSIS IRQn enum (variants/<chip>/LPC8xx.h). Reserved slots keep Default_Handler.
• Other variants (LPC812/LPC824/...): unchanged — legacy all-default table until someone adds their map.
• NMI weak-alias fix: the fault-emit branch declared NMI_Handler as a strong alias of HardFault_Handler, so nothing downstream could override NMI (the no-fault-emit branch was already weak). Now weak in both. FastLED routes the WWDT warning interrupt to NMI via SYSCON->NMISRC for pre-reset wedge backtraces (validated on LPC845-BRK silicon 2026-07-02) and may install a WDT-labeled report.

Compatibility

Zero behavior change for existing code: every named handler weak-aliases to the same Default_Handler as before; the table is link-time identical unless a consumer defines a strong override. .isr_vector size unchanged (48 entries).

🤖 Generated with Claude Code

Summary by CodeRabbit

• Bug Fixes
  • Improved interrupt handling on LPC8xx boards so chip-specific IRQs now map to the correct handlers instead of all falling back to a generic default.
  • Made the non-maskable interrupt handler overrideable, allowing sketches and libraries to provide their own behavior.
  • Preserved default behavior for reserved or unsupported interrupt slots on other chips.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: e803c1cb-31bd-453c-a512-d60f2838f8a8

📥 Commits

Reviewing files that changed from the base of the PR and between fd73dae and 293ea91.

📒 Files selected for processing (1)

• cores/lpc8xx/startup_lpc8xx.c

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📝 Walkthrough

Walkthrough

The vector table in startup_lpc8xx.c is updated to use chip-specific, individually overridable weak IRQ handler symbols for LPC845 and LPC804 variants, replacing the previous scheme where all chip-level IRQ slots pointed to Default_Handler. NMI_Handler's alias is also made weak.

Changes

LPC8xx Weak IRQ Handler Mapping

Layer / File(s)	Summary
Weak IRQ handler declarations cores/lpc8xx/startup_lpc8xx.c	NMI_Handler alias changed to weak; new weak IRQ handler symbols declared for LPC845 and LPC804 chip variants, each aliasing Default_Handler.
Vector table chip-specific mapping cores/lpc8xx/startup_lpc8xx.c	Vector table IRQ slots conditionally reference the new per-chip weak handlers for LPC845/LPC804, keep reserved slots on Default_Handler, and preserve the legacy all-default mapping for other chips.

Estimated code review effort: 3 (Moderate) | ~20 minutes

Related PRs: None specified.

Suggested labels: enhancement, lpc8xx

Suggested reviewers: None specified.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly summarizes the main change: named weak IRQ handlers for LPC845/LPC804 startup vector slots.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
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🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch feat/named-weak-irq-handlers

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