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fix for serial port on esp32 (#5501) #5503

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fix for serial port on esp32 (#5501) #5503

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12 changes: 9 additions & 3 deletions wled00/wled.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -11,6 +11,9 @@
#include "soc/soc.h"
#include "soc/rtc_cntl_reg.h"
#endif
#ifdef ARDUINO_ARCH_ESP32
#include "driver/gpio.h"
#endif

extern "C" void usePWMFixedNMI();

Expand Down Expand Up @@ -368,13 +371,16 @@ void WLED::setup()
WRITE_PERI_REG(RTC_CNTL_BROWN_OUT_REG, 0); //disable brownout detection
#endif

#ifdef ARDUINO_ARCH_ESP32
pinMode(hardwareRX, INPUT_PULLDOWN); delay(1); // suppress noise in case RX pin is floating (at low noise energy) - see issue #3128
#endif
#ifdef WLED_BOOTUPDELAY
delay(WLED_BOOTUPDELAY); // delay to let voltage stabilize, helps with boot issues on some setups
#endif
Serial.begin(115200);
#ifdef ARDUINO_ARCH_ESP32
// Pull down RX pin to suppress noise when floating, without breaking UART0 IOMUX mapping.
// pinMode() routes GPIO through the GPIO matrix and detaches UART0 RX - use gpio_pulldown_en() instead.
// See issue #3128.
gpio_pulldown_en((gpio_num_t)hardwareRX);
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@DedeHai DedeHai Apr 13, 2026

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

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@softhack007 softhack007 Apr 14, 2026

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@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.

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@DedeHai DedeHai Apr 14, 2026

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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.

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@DedeHai DedeHai Apr 14, 2026

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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.

#endif
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softhack007 marked this conversation as resolved.
#if !ARDUINO_USB_CDC_ON_BOOT
Serial.setTimeout(50); // this causes troubles on new MCUs that have a "virtual" USB Serial (HWCDC)
#else
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