fix for serial port on esp32 (#5501)

[RobertoD91]

Possible fix for #5501
Tested on a real ESP32, and CI passes. It has not been tested on a real ESP8266.

This is my first pull request, so please feel free to reject it if anything is wrong.

Summary by CodeRabbit

• Chores
  • Refined ESP32 serial communication initialization during startup for improved stability and hardware compatibility.

[coderabbitai]

Walkthrough

The RX pin initialization on ESP32 is refactored to use the GPIO driver's gpio_pulldown_en() function instead of Arduino's pinMode(), placed after Serial.begin() to avoid UART IOMUX interference. This requires adding driver/gpio.h.

Changes

Cohort / File(s)	Summary
ESP32 RX Pin Initialization wled00/wled.cpp	Replaced pinMode(hardwareRX, INPUT_PULLDOWN) with direct GPIO driver call gpio_pulldown_en() invoked after serial initialization, including driver/gpio.h header to prevent UART IOMUX conflicts on ESP32.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

🚥 Pre-merge checks | ✅ 2 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (2 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately describes the main change: fixing serial port initialization on ESP32 by replacing pinMode() with gpio_pulldown_en().

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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[coderabbitai]

Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against the current code and only fix it if needed.

Inline comments:
In `@wled00/wled.cpp`:
- Around line 378-383: The serial RX timeout is too long on ESP32 causing
Serial.available() to miss short commands; after the existing
Serial.begin(115200) call add a guarded call to Serial.setRxTimeout(1) inside
the preprocessor check for ARDUINO_ARCH_ESP32 and excluding
ARDUINO_USB_CDC_ON_BOOT (i.e. wrap the setRxTimeout call with `#if`
defined(ARDUINO_ARCH_ESP32) && !ARDUINO_USB_CDC_ON_BOOT ... `#endif`) so the IDF
idle-timeout mechanism triggers for short packets without using setRxFIFOFull();
keep the existing gpio_pulldown_en((gpio_num_t)hardwareRX) code as-is.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

Plan: Pro

Run ID: 86d25caf-0e0d-43d3-a53d-58111982b7fc

📥 Commits

Reviewing files that changed from the base of the PR and between 9651061 and 1cce33e.

📒 Files selected for processing (1)

• wled00/wled.cpp

[DedeHai]

all that is needed is to replace pinMode(hardwareRX, INPUT_PULLDOWN); with this line, nothing else.

[softhack007]

@DedeHai originally the pinMode() call was located before Serial.Begin(), to avoid side-effects when Serial initializes its pins. 🤔 Do you think gpio_pulldown_en() should happen before Serial.Begin(), or keep it after? I don't have much experience with the under-the-hood pin config tools in esp-idf.

[DedeHai]

it should stay where it was, the API calls are very low level and will directly write the GPIO registers, enabling the pulldown with no fuss.

[DedeHai]

I can confirm the fix working, all that is needed is this:
replace
pinMode(hardwareRX, INPUT_PULLDOWN);
with
gpio_pulldown_en((gpio_num_t)hardwareRX);
and maybe add a comment that pinMode() sets the gpio mux and breaks UART.

no additional includes, nothing.