[EricSchubert]

Supersedes #280, which had to be closed after a force-push broke its
shared history with develop (see #280 for the full review discussion
with @julianneswinoga — all her feedback is addressed in this branch).

Adds RP2040 support for two boards:

• JackW01 Pi Pico printer carrier board
• BTT SKR Pico v1.0

All review comments from #280 are addressed:

• Restored INFO_DISPLAY_UPSIDE_DOWN/INFO_DISPLAY_MIRRORED defines and
  the OAE validation branch that were accidentally dropped
• Removed references to unimplemented boards (bare Pico, RP2350)
• Fixed invalid @Version library specs in platformio.ini (should be
  #version for git-hosted deps)
• Reverted an unrelated Mount.cpp/Mount.hpp refactor that had been
  bundled into the port, keeping only the toff(1)->toff(4) change
  actually needed for TMC2209 StealthChop on RP2040

Verified: rp2040_jackw01 and rp2040_skr_pico build and flash cleanly;
SKR Pico hardware responds correctly to Meade protocol commands.

[ClutchplateDude]

Hey Eric,
thanks for your contribution, sorry that we are only now getting around to looking at this, and thanks for carrying over all of julianne's feedback from #280.
The platform work itself is in good shape: the RP2040 alarm-timer implementation in InterruptCallback.cpp, the flash-backed EEPROM path in EPROMStore.cpp, the board pin files, and the [common_rp2xxx] platformio setup (the Philhower core is the right call for UART remapping) are all cleanly done and easy to review. That's the hard part, and it's done.

Unfortunately I have to ask for one more pass, because the branch as it stands would silently revert several released features - that's the real blocker, not the merge conflicts.

The problem

The branch is based on V1.13.19, but it isn't a superset of it: in the shared files, the older versions from your fork won, so the diff deletes things develop shipped in V1.13.12–V1.13.19. None of these deletions show up as merge conflicts - they would merge cleanly and quietly.
Specifically, the branch removes:

• OAE v1 board support entirely - [env:oaeboardv1] from platformio.ini, boards/ESP32_ESP32DEV/pins_OAE_V1.hpp, all OAE ifdefs in Configuration_adv.hpp, and the OAE variant of the SSD1306 driver.
• The test menu (TEST_VERIFY_MODE, ~850 lines across src/testmenu.* plus its f_serial.hpp integration).
• matrix_build_parallel.py (added in V1.13.12 to speed up CI matrix builds).
• AZ/ALT steps-per-degree EEPROM storage - those functions are still called from Mount.cpp, so this one is also a compile break.
• Various Meade doc improvements, homing log lines, and the Changelog gets rewound to the V1.13.11 era.

My guess is the fork started life from a pre-V1.13.12 tree, and when the V1.13.19 content came in, whole files were taken from the old side - an easy trap, especially after the #280 history break. No worries, but it does need fixing before this can land.

Suggested path

A plain rebase will be painful because develop's Meade-parser rewrite (#291), the core refactor (#293), and the coordinate-handling fixes (#300–#305) touch exactly the files this PR modifies.
I'd instead start fresh:

1. Create a new branch off current develop (and push it to this PR — same fork branch is fine).
2. Copy over the RP2040-only additions:
   • boards/RP2040_JACKW01/, boards/RP2040_SKR_PICO/, boards/RP2040_PICO/ pin files
   • Configuration_local_examples/Configuration_local_rp2040_skr_pico.hpp
   • [common_rp2xxx] plus the two rp2040_* envs in platformio.ini - keeping [env:oaeboardv1] exactly as it is on develop
   • the ARDUINO_ARCH_RP2040 sections in InterruptCallback.cpp and EPROMStore.cpp
   • the board IDs in Constants.hpp, the ARDUINO_ARCH_RP2040 guards in the shared sources, and the new boards in matrix_build.py / README
3. Re-apply the #elif defined(ARDUINO_ARCH_RP2040) guards against the current file contents rather than the old ones - most should only be a few lines each.
4. Please leave Version.h and Changelog.md untouched - release-please maintains them now, and edits there will conflict on every future rebase.

One change to discuss separately

The toff(1) → toff(4) change in Mount.cpp isn't behind an RP2040 guard, so it changes TMC2209 chopper timing on AVR and ESP32 as well. If it's required for StealthChop on RP2040, please wrap it in #if defined(ARDUINO_ARCH_RP2040) for now. If you believe toff(4) is correct everywhere (the datasheet does recommend ≥3 for slow decay), that's worth its own PR where it can be tested per-platform.

Two smaller notes:

• The red clang-format check from August was infrastructure, not your code - the workflow used pull_request_target and refused to check out the fork. That's fixed on develop, so CI will run for real on your next push.
• Since develop's stepper and Meade code has moved under you since your hardware verification, a quick smoke test on the SKR Pico after the rebase would be great.

The rough shape to aim for: additive only - every hunk in the diff should either add RP2040 code or be a guard around it. If it deletes or rewrites something that already exists on develop, it probably shouldn't be in this PR.

Happy to help with the specifics if anything here is unclear - RP2040 support is very much wanted, it just needs to land as a pure addition on top of current develop. And if you'd prefer, I can also cherry-pick the platform pieces into a clean branch on my side so you only have to review and verify on hardware.

[EricSchubert]

@ClutchplateDude, I believe I've managed to create a new branch with my SKR Pico support built on the latest main branch. The PR should be updated with those changes. Let me know if anything was missed or broken.