[ESP32-S3] UART0 pins cannot be assigned to UART1 or UART2 in 3.3.6 and later

[nomakewan]

Board

ESP32-S3 N16R8

Device Description

Both the ESP32-S3 N16R8 dev kit and a fully custom PCB using the ESP32-S3 N16R8 as a bare microcontroller with no CP2102 bridge chip.

Hardware Configuration

Board is in USB-CDC mode (pins 19/20 are connected to USB-C port), eFuse UART_PRINT_CONTROL is set to 0b11, eFuse DIS_PAD_JTAG is set to 0b1.

Version

v3.3.7

Type

Bug

IDE Name

Arduino IDE and VSCode with PlatformIO

Operating System

Windows 10

Flash frequency

80MHz

PSRAM enabled

yes

Upload speed

115200

Description

(Continued from #12277 and #12386)

On Arduino-ESP32 3.3.6 and later frameworks, pin 43 (by default, UART0 TX) cannot be reassigned to TX for UART1 or UART2. On Arduino-ESP32 3.3.5 or earlier, pin 43 can be reassigned to any UART peripheral on the micro without any issues.

Sketch

#include <Arduino.h>

#define TEST_INTERVAL 5000  // ms between tests
#define BAUD_RATE 115200
#define TEST_TIMEOUT 1000   // ms to wait for response

unsigned long serial1ToSerial0Success = 0;
unsigned long serial1ToSerial0Fail = 0;

unsigned long lastTestTime = 0;

void printUARTStatus(const char* name, HardwareSerial &serial) {
  Serial.printf("\n=== %s Status ===\n", name);
  Serial.printf("  Bytes available to read: %d\n", serial.available());
}

void printStats() {
  Serial.println("\n========== Serial Test Statistics ==========");
  Serial.printf("Serial1 -> Serial0: %lu passed, %lu failed (%.1f%% success)\n",
                serial1ToSerial0Success,
                serial1ToSerial0Fail,
                (serial1ToSerial0Success + serial1ToSerial0Fail) > 0
                  ? (100.0 * serial1ToSerial0Success / (serial1ToSerial0Success + serial1ToSerial0Fail))
                  : 0.0);
  Serial.println("============================================\n");
}

bool testSerialPair(HardwareSerial &sender, HardwareSerial &receiver, const char* direction) {
  static unsigned long testCounter = 0;
  testCounter++;
  String testMessage = String("TEST:") + testCounter + ":" + millis();

  Serial.printf("[%s] Sending: %s\n", direction, testMessage.c_str());

  // Clear receiver buffer
  while (receiver.available()) {
    receiver.read();
  }

  // Send test message
  sender.println(testMessage);
  sender.flush();

  // Debug: Check UART status after sending
  Serial.printf("[%s] After flush, checking receiver status...\n", direction);
  if (strcmp(direction, "S1->S0") == 0) {
    printUARTStatus("Serial0 (receiver)", receiver);
  } else {
    printUARTStatus("Serial1 (receiver)", receiver);
  }

  // Wait for response
  unsigned long startTime = millis();
  String received = "";
  bool success = false;
  int bytesRead = 0;

  while (millis() - startTime < TEST_TIMEOUT) {
    if (receiver.available()) {
      char c = receiver.read();
      bytesRead++;
      if (c == '\n') {
        break;
      }
      if (c != '\r') {
        received += c;
      }
    }
    delay(1);
  }

  // Verify received message
  Serial.printf("[%s] Read %d bytes, received: '%s'\n", direction, bytesRead, received.c_str());

  if (received == testMessage) {
    Serial.printf("[%s] SUCCESS - Message verified\n", direction);
    success = true;
  } else {
    Serial.printf("[%s] FAILED - Expected: %s, Got: %s\n",
                  direction, testMessage.c_str(),
                  received.length() > 0 ? received.c_str() : "(nothing)");
    success = false;
  }

  return success;
}

void setup() {
  setCpuFrequencyMhz(160);
  Serial.begin(115200);
  Serial0.end();

  Serial1.begin(9600, SERIAL_8N1, 44, 43);
  Serial0.begin(9600, SERIAL_8N1, 11, 10);
}

// The main loop of the program which manages all system operations which must occur on every loop.
void loop() {
  unsigned long currentTime = millis();

  if (currentTime - lastTestTime >= TEST_INTERVAL) {
    lastTestTime = currentTime;

    Serial.println("\n--- Testing Serial1 -> Serial0 ---");
    bool success = testSerialPair(Serial1, Serial0, "S1->S0");
    //bool success = testSerialPair(Serial0, Serial1, "S0->S1");
    if (success) {
      serial1ToSerial0Success++;
    } else {
      serial1ToSerial0Fail++;
    }

    if ((serial1ToSerial0Success + serial1ToSerial0Fail) % 2 == 0) {
      printStats();
    }
  }
}

Debug Message

=========== Before Setup Start ===========
Chip Info:
------------------------------------------
  Model             : ESP32-S3
  Package           : 0
  Revision          : 0.02
  Cores             : 2
  CPU Frequency     : 160 MHz
  XTAL Frequency    : 40012
  Embedded Flash    : No
  Embedded PSRAM    : No
  2.4GHz WiFi       : Yes
  Classic BT        : No
  BT Low Energy     : Yes
  IEEE 802.15.4     : No
------------------------------------------
INTERNAL Memory Info:
------------------------------------------
  Total Size        :   390152 B ( 381.0 KB)
  Free Bytes        :   350972 B ( 342.7 KB)
  Allocated Bytes   :    33596 B (  32.8 KB)
  Minimum Free Bytes:   345824 B ( 337.7 KB)
  Largest Free Block:   294900 B ( 288.0 KB)
------------------------------------------
Flash Info:
------------------------------------------
  Chip Size         : 16777216 B (16 MB)
  Block Size        :    65536 B (  64.0 KB)
  Sector Size       :     4096 B (   4.0 KB)
  Page Size         :      256 B (   0.2 KB)
  Bus Speed         : 80 MHz
  Flash Frequency   : 80 MHz (source: 80 MHz, divider: 1)
  Bus Mode          : QIO
------------------------------------------
Partitions Info:
------------------------------------------
                nvs : addr: 0x00009000, size:    20.0 KB, type: DATA, subtype: NVS
            otadata : addr: 0x0000E000, size:     8.0 KB, type: DATA, subtype: OTA
               app0 : addr: 0x00010000, size:  1280.0 KB, type:  APP, subtype: OTA_0
               app1 : addr: 0x00150000, size:  1280.0 KB, type:  APP, subtype: OTA_1
             spiffs : addr: 0x00290000, size:  1408.0 KB, type: DATA, subtype: SPIFFS
           coredump : addr: 0x003F0000, size:    64.0 KB, type: DATA, subtype: COREDUMP
------------------------------------------
Software Info:
------------------------------------------
  Compile Date/Time : Feb 23 2026 16:10:07
  Compile Host OS   : windows
  ESP-IDF Version   : v5.5.2-729-g87912cd291
  Arduino Version   : 3.3.7
------------------------------------------
Board Info:
------------------------------------------
  Arduino Board     : ESP32S3_DEV
  Arduino Variant   : esp32s3
  Arduino FQBN      : esp32:esp32:esp32s3:UploadSpeed=921600,USBMode=hwcdc,CDCOnBoot=cdc,MSCOnBoot=default,DFUOnBoot=default,UploadMode=default,CPUFreq=160,FlashMode=qio,FlashSize=16M,PartitionScheme=default,DebugLevel=debug,PSRAM=disabled,LoopCore=1,EventsCore=1,EraseFlash=none,JTAGAdapter=default,ZigbeeMode=default
============ Before Setup End ============
[  3586][I][esp32-hal-periman.c:141] perimanSetPinBus(): Pin 19 already has type USB_DM (45) with bus 0x3fc98358
[  3586][I][esp32-hal-periman.c:141] perimanSetPinBus(): Pin 20 already has type USB_DP (46) with bus 0x3fc98358
[  3587][D][esp32-hal-uart.c:294] _uartDetachBus_RX(): _uartDetachBus_RX: RX pin already detached for UART0
[  3588][D][esp32-hal-uart.c:313] _uartDetachBus_TX(): _uartDetachBus_TX: TX pin already detached for UART0
=========== After Setup Start ============
INTERNAL Memory Info:
------------------------------------------
  Total Size        :   390152 B ( 381.0 KB)
  Free Bytes        :   346228 B ( 338.1 KB)
  Allocated Bytes   :    37796 B (  36.9 KB)
  Minimum Free Bytes:   341080 B ( 333.1 KB)
  Largest Free Block:   294900 B ( 288.0 KB)
------------------------------------------
GPIO Info:
------------------------------------------
  GPIO : BUS_TYPE[bus/unit][chan]
  --------------------------------------  
    10 : UART_TX[0]
    11 : UART_RX[0]
    19 : USB_DM
    20 : USB_DP
    43 : UART_TX[1]
    44 : UART_RX[1]
============ After Setup End =============

--- Testing Serial1 -> Serial0 ---
[S1->S0] Sending: TEST:1:5000
[S1->S0] After flush, checking receiver status...

=== Serial0 (receiver) Status ===
  Bytes available to read: 0
[S1->S0] Read 0 bytes, received: ''
[S1->S0] FAILED - Expected: TEST:1:5000, Got: (nothing)

--- Testing Serial1 -> Serial0 ---
[S1->S0] Sending: TEST:2:10000
[S1->S0] After flush, checking receiver status...

=== Serial0 (receiver) Status ===
  Bytes available to read: 0
[S1->S0] Read 0 bytes, received: ''
[S1->S0] FAILED - Expected: TEST:2:10000, Got: (nothing)

========== Serial Test Statistics ==========
Serial1 -> Serial0: 0 passed, 2 failed (0.0% success)
============================================

Other Steps to Reproduce

Please note that while the debug sketch fails on Arduino-ESP32 3.3.6 and 3.3.7, it will work properly on 3.3.5 and earlier. This is not a hardware problem, nor is it in any way related to devkit boards having a CP2102 bridge chip onboard (our custom hardware has no such bridge chip and experiences the same issue with 3.3.6 and later frameworks).

I have checked existing issues, online documentation and the Troubleshooting Guide

• I confirm I have checked existing issues, online documentation and Troubleshooting guide.

[SuGlider]

@nomakewan - I have found the root cause of the issue. Still analyzing the best way to solve it.

But I have found a workaround using the current implementation of Arduino Core 3.3.7.
You can try it:

Add to your settings:

-DNO_GLOBAL_SERIAL
-DSerial=HWCDCSerial

#include <Arduino.h>

///////////////////////////////////////   Added Code to the original sketch
#ifdef NO_GLOBAL_SERIAL
HardwareSerial Serial0(0);
HardwareSerial Serial1(1);
HardwareSerial Serial2(2);

// C-callable helper used by HAL when pins are detached and the high-level
// HardwareSerial instance must be finalized.
// Moved from HardwareSerial.cpp to here because it is removed from the Core code due to -DNO_GLOBAL_SERIAL
// Necessary for linking the final firmware
extern "C" void hal_uart_notify_pins_detached(int uart_num) {
  log_d("hal_uart_notify_pins_detached: Notifying HardwareSerial for UART%d", uart_num);
  switch (uart_num) {
    case 0: Serial0.end(); break;
#if SOC_UART_NUM > 1
    case 1: Serial1.end(); break;
#endif
#if SOC_UART_NUM > 2
    case 2: Serial2.end(); break;
#endif
#if SOC_UART_NUM > 3
    case 3: Serial3.end(); break;
#endif
#if SOC_UART_NUM > 4
    case 4: Serial4.end(); break;
#endif
#if SOC_UART_NUM > 5
    case 5: Serial5.end(); break;
#endif
    default: log_e("hal_uart_notify_pins_detached: UART%d not handled!", uart_num); break;
  }
}
#endif
///////////////////////////////////////   Added Code to the original sketch

#define TEST_INTERVAL 5000  // ms between tests
#define BAUD_RATE 115200
#define TEST_TIMEOUT 1000   // ms to wait for response

unsigned long serial1ToSerial0Success = 0;
unsigned long serial1ToSerial0Fail = 0;

unsigned long lastTestTime = 0;

void printUARTStatus(const char* name, HardwareSerial &serial) {
  Serial.printf("\n=== %s Status ===\n", name);
  Serial.printf("  Bytes available to read: %d\n", serial.available());
}

void printStats() {
  Serial.println("\n========== Serial Test Statistics ==========");
  Serial.printf("Serial1 -> Serial0: %lu passed, %lu failed (%.1f%% success)\n",
                serial1ToSerial0Success,
                serial1ToSerial0Fail,
                (serial1ToSerial0Success + serial1ToSerial0Fail) > 0
                  ? (100.0 * serial1ToSerial0Success / (serial1ToSerial0Success + serial1ToSerial0Fail))
                  : 0.0);
  Serial.println("============================================\n");
}

bool testSerialPair(HardwareSerial &sender, HardwareSerial &receiver, const char* direction) {
  static unsigned long testCounter = 0;
  testCounter++;
  String testMessage = String("TEST:") + testCounter + ":" + millis();

  Serial.printf("[%s] Sending: %s\n", direction, testMessage.c_str());

  // Clear receiver buffer
  while (receiver.available()) {
    receiver.read();
  }

  // Send test message
  sender.println(testMessage);
  sender.flush();

  // Debug: Check UART status after sending
  Serial.printf("[%s] After flush, checking receiver status...\n", direction);
  if (strcmp(direction, "S1->S0") == 0) {
    printUARTStatus("Serial0 (receiver)", receiver);
  } else {
    printUARTStatus("Serial1 (receiver)", receiver);
  }

  // Wait for response
  unsigned long startTime = millis();
  String received = "";
  bool success = false;
  int bytesRead = 0;

  while (millis() - startTime < TEST_TIMEOUT) {
    if (receiver.available()) {
      char c = receiver.read();
      bytesRead++;
      if (c == '\n') {
        break;
      }
      if (c != '\r') {
        received += c;
      }
    }
    delay(1);
  }

  // Verify received message
  Serial.printf("[%s] Read %d bytes, received: '%s'\n", direction, bytesRead, received.c_str());

  if (received == testMessage) {
    Serial.printf("[%s] SUCCESS - Message verified\n", direction);
    success = true;
  } else {
    Serial.printf("[%s] FAILED - Expected: %s, Got: %s\n",
                  direction, testMessage.c_str(),
                  received.length() > 0 ? received.c_str() : "(nothing)");
    success = false;
  }

  return success;
}

void setup() {
  setCpuFrequencyMhz(160);
  Serial.begin();
  Serial0.end();

  Serial1.begin(9600, SERIAL_8N1, 44, 43);
  Serial0.begin(9600, SERIAL_8N1, 11, 10);
}

// The main loop of the program which manages all system operations which must occur on every loop.
void loop() {
  unsigned long currentTime = millis();

  if (currentTime - lastTestTime >= TEST_INTERVAL) {
    lastTestTime = currentTime;

    Serial.println("\n--- Testing Serial1 -> Serial0 ---");
    bool success = testSerialPair(Serial1, Serial0, "S1->S0");
    //bool success = testSerialPair(Serial0, Serial1, "S0->S1");
    if (success) {
      serial1ToSerial0Success++;
    } else {
      serial1ToSerial0Fail++;
    }

    if ((serial1ToSerial0Success + serial1ToSerial0Fail) % 2 == 0) {
      printStats();
    }
  }
}

OUTPUT:

=========== Before Setup Start ===========
Chip Info:
------------------------------------------
  Model             : ESP32-S3
  Package           : 0
  Revision          : 0.01
  Cores             : 2
  CPU Frequency     : 240 MHz
  XTAL Frequency    : 40 MHz
  Features Bitfield : 0x00000012
  Embedded Flash    : No
  Embedded PSRAM    : No
  2.4GHz WiFi       : Yes
  Classic BT        : No
  BT Low Energy     : Yes
  IEEE 802.15.4     : No
------------------------------------------
INTERNAL Memory Info:
------------------------------------------
  Total Size        :   390152 B ( 381.0 KB)
  Free Bytes        :   351060 B ( 342.8 KB)
  Allocated Bytes   :    33540 B (  32.8 KB)
  Minimum Free Bytes:   345912 B ( 337.8 KB)
  Largest Free Block:   294900 B ( 288.0 KB)
------------------------------------------
Flash Info:
------------------------------------------
  Chip Size         :  8388608 B (8 MB)
  Block Size        :    65536 B (  64.0 KB)
  Sector Size       :     4096 B (   4.0 KB)
  Page Size         :      256 B (   0.2 KB)
  Bus Speed         : 80 MHz
  Flash Frequency   : 80 MHz (source: 80 MHz, divider: 1)
  Bus Mode          : QIO
------------------------------------------
Partitions Info:
------------------------------------------
                nvs : addr: 0x00009000, size:    20.0 KB, type: DATA, subtype: NVS
            otadata : addr: 0x0000E000, size:     8.0 KB, type: DATA, subtype: OTA
               app0 : addr: 0x00010000, size:  1280.0 KB, type:  APP, subtype: OTA_0
               app1 : addr: 0x00150000, size:  1280.0 KB, type:  APP, subtype: OTA_1
             spiffs : addr: 0x00290000, size:  1408.0 KB, type: DATA, subtype: SPIFFS
           coredump : addr: 0x003F0000, size:    64.0 KB, type: DATA, subtype: COREDUMP
------------------------------------------
Software Info:
------------------------------------------
  Compile Date/Time : Feb 24 2026 23:21:19
  Compile Host OS   : windows
  ESP-IDF Version   : v5.5.2-729-g87912cd291
  Arduino Version   : 3.3.7
------------------------------------------
Board Info:
------------------------------------------
  Arduino Board     : ESP32S3_DEV
  Arduino Variant   : esp32s3
  Arduino FQBN      : esp32:esp32:esp32s3:UploadSpeed=921600,USBMode=hwcdc,CDCOnBoot=cdc,MSCOnBoot=default,DFUOnBoot=default,UploadMode=default,CPUFreq=240,FlashMode=qio,FlashSize=4M,PartitionScheme=default,DebugLevel=verbose,PSRAM=disabled,LoopCore=1,EventsCore=1,EraseFlash=none,JTAGAdapter=default,ZigbeeMode=default
============ Before Setup End ============
[  1264][D][esp32-hal-cpu.c:316] setCpuFrequencyMhz(): PLL: 480 / 3 = 160 Mhz, APB: 80000000 Hz
[  1265][I][esp32-hal-periman.c:141] perimanSetPinBus(): Pin 19 already has type USB_DM (45) with bus 0x3fc9843c
[  1265][I][esp32-hal-periman.c:141] perimanSetPinBus(): Pin 20 already has type USB_DP (46) with bus 0x3fc9843c
[  1266][V][esp32-hal-uart.c:641] uartBegin(): UART1 baud(9600) Mode(800001c) rxPin(44) txPin(43)
[  1266][V][esp32-hal-uart.c:739] uartBegin(): UART1 not installed. Starting installation
[  1267][V][esp32-hal-uart.c:749] uartBegin(): UART1 RX FIFO full threshold set to 120 (value requested: 120 || FIFO Max = 128)
[  1268][V][esp32-hal-uart.c:775] uartBegin(): Setting UART1 to use XTAL clock
[  1269][V][esp32-hal-uart.c:814] uartBegin(): UART1: RX and TX signals are set not inverted.
[  1269][V][esp32-hal-periman.c:251] perimanClearBusDeinit(): Deinit function for type UART_RX (2) cleared
[  1270][V][esp32-hal-periman.c:251] perimanClearBusDeinit(): Deinit function for type UART_TX (3) cleared
[  1271][V][esp32-hal-periman.c:251] perimanClearBusDeinit(): Deinit function for type UART_CTS (4) cleared
[  1271][V][esp32-hal-periman.c:251] perimanClearBusDeinit(): Deinit function for type UART_RTS (5) cleared
[  1272][V][esp32-hal-periman.c:160] perimanSetPinBus(): Pin 44 successfully set to type UART_RX (2) with bus 0x3fc94a28
[  1272][V][esp32-hal-periman.c:235] perimanSetBusDeinit(): Deinit function for type UART_RX (2) successfully set to 0x4200656c
[  1273][V][esp32-hal-periman.c:160] perimanSetPinBus(): Pin 43 successfully set to type UART_TX (3) with bus 0x3fc94a28
[  1274][V][esp32-hal-periman.c:235] perimanSetBusDeinit(): Deinit function for type UART_TX (3) successfully set to 0x42006488
[  1275][V][esp32-hal-uart.c:842] uartBegin(): UART1 initialization done.
[  1275][V][esp32-hal-uart.c:893] uartSetRxFIFOFull(): UART1 RX FIFO Full value set to 1 from a requested value of 1
[  1276][V][esp32-hal-uart.c:641] uartBegin(): UART0 baud(9600) Mode(800001c) rxPin(11) txPin(10)
[  1276][V][esp32-hal-uart.c:739] uartBegin(): UART0 not installed. Starting installation
[  1277][V][esp32-hal-uart.c:749] uartBegin(): UART0 RX FIFO full threshold set to 120 (value requested: 120 || FIFO Max = 128)
[  1278][V][esp32-hal-uart.c:775] uartBegin(): Setting UART0 to use XTAL clock
[  1278][V][esp32-hal-uart.c:814] uartBegin(): UART0: RX and TX signals are set not inverted.
[  1279][V][esp32-hal-periman.c:251] perimanClearBusDeinit(): Deinit function for type UART_RX (2) cleared
[  1280][V][esp32-hal-periman.c:251] perimanClearBusDeinit(): Deinit function for type UART_TX (3) cleared
[  1280][V][esp32-hal-periman.c:251] perimanClearBusDeinit(): Deinit function for type UART_CTS (4) cleared
[  1281][V][esp32-hal-periman.c:251] perimanClearBusDeinit(): Deinit function for type UART_RTS (5) cleared
[  1281][V][esp32-hal-periman.c:160] perimanSetPinBus(): Pin 11 successfully set to type UART_RX (2) with bus 0x3fc94a04
[  1282][V][esp32-hal-periman.c:235] perimanSetBusDeinit(): Deinit function for type UART_RX (2) successfully set to 0x4200656c
[  1283][V][esp32-hal-periman.c:160] perimanSetPinBus(): Pin 10 successfully set to type UART_TX (3) with bus 0x3fc94a04
[  1284][V][esp32-hal-periman.c:235] perimanSetBusDeinit(): Deinit function for type UART_TX (3) successfully set to 0x42006488
[  1284][V][esp32-hal-periman.c:235] perimanSetBusDeinit(): Deinit function for type UART_RX (2) successfully set to 0x4200656c
[  1285][V][esp32-hal-periman.c:235] perimanSetBusDeinit(): Deinit function for type UART_TX (3) successfully set to 0x42006488
[  1286][V][esp32-hal-uart.c:842] uartBegin(): UART0 initialization done.
[  1286][V][esp32-hal-uart.c:893] uartSetRxFIFOFull(): UART0 RX FIFO Full value set to 1 from a requested value of 1
=========== After Setup Start ============
INTERNAL Memory Info:
------------------------------------------
  Total Size        :   390152 B ( 381.0 KB)
  Free Bytes        :   346316 B ( 338.2 KB)
  Allocated Bytes   :    37740 B (  36.9 KB)
  Minimum Free Bytes:   341020 B ( 333.0 KB)
  Largest Free Block:   294900 B ( 288.0 KB)
------------------------------------------
GPIO Info:
------------------------------------------
  GPIO : BUS_TYPE[bus/unit][chan]
  --------------------------------------  
    10 : UART_TX[0]
    11 : UART_RX[0]
    19 : USB_DM
    20 : USB_DP
    43 : UART_TX[1]
    44 : UART_RX[1]
============ After Setup End =============

--- Testing Serial1 -> Serial0 ---
[S1->S0] Sending: TEST:1:5000
[S1->S0] After flush, checking receiver status...

=== Serial0 (receiver) Status ===
  Bytes available to read: 13
[S1->S0] Read 13 bytes, received: 'TEST:1:5000'
[S1->S0] SUCCESS - Message verified

--- Testing Serial1 -> Serial0 ---
[S1->S0] Sending: TEST:2:10000
[S1->S0] After flush, checking receiver status...

=== Serial0 (receiver) Status ===
  Bytes available to read: 14
[S1->S0] Read 14 bytes, received: 'TEST:2:10000'
[S1->S0] SUCCESS - Message verified

========== Serial Test Statistics ==========
Serial1 -> Serial0: 2 passed, 0 failed (100.0% success)
============================================

[SuGlider]

Interesting; I'm using 3.3.7 on PlatformIO and when I try to add those compiler flags, I get a linker error:

Linking .pio\build\esp32s3\firmware.elf
C:/platform-io/packages/toolchain-xtensa-esp-elf/bin/../lib/gcc/xtensa-esp-elf/14.2.0/../../../../xtensa-esp-elf/bin/ld.exe: .pio/build/esp32s3/libFrameworkArduino.a(esp32-hal-uart.c.o):(.literal._uartDetachBus_TX+0x8): undefined reference to `hal_uart_notify_pins_detached'
C:/platform-io/packages/toolchain-xtensa-esp-elf/bin/../lib/gcc/xtensa-esp-elf/14.2.0/../../../../xtensa-esp-elf/bin/ld.exe: .pio/build/esp32s3/libFrameworkArduino.a(esp32-hal-uart.c.o): in function `_uartDetachBus_TX':
C:/platform-io/packages/framework-arduinoespressif32/cores/esp32/esp32-hal-uart.c:318:(.text._uartDetachBus_TX+0x52): undefined reference to `hal_uart_notify_pins_detached'
C:/platform-io/packages/toolchain-xtensa-esp-elf/bin/../lib/gcc/xtensa-esp-elf/14.2.0/../../../../xtensa-esp-elf/bin/ld.exe: .pio/build/esp32s3/libFrameworkArduino.a(esp32-hal-uart.c.o): in function `_uartDetachBus_RX':
C:/platform-io/packages/framework-arduinoespressif32/cores/esp32/esp32-hal-uart.c:299:(.text._uartDetachBus_RX+0x52): undefined reference to `hal_uart_notify_pins_detached'
collect2.exe: error: ld returned 1 exit status
*** [.pio\build\esp32s3\firmware.elf] Error 1

yes, the NO_GLOBAL_SERIAL prevents the compilation of the C function hal_uart_notify_pins_detached(), which is inside HardwareSerial.ccp file in the Core Code.

Ther is why you may need to add it separately inside your sketch, as I have shown in the code I've posted above.

#ifdef NO_GLOBAL_SERIAL
HardwareSerial Serial0(0);
HardwareSerial Serial1(1);
HardwareSerial Serial2(2);

// C-callable helper used by HAL when pins are detached and the high-level
// HardwareSerial instance must be finalized.
// Moved from HardwareSerial.cpp to here because it is removed from the Core code due to -DNO_GLOBAL_SERIAL
// Necessary for linking the final firmware
extern "C" void hal_uart_notify_pins_detached(int uart_num) {
  log_d("hal_uart_notify_pins_detached: Notifying HardwareSerial for UART%d", uart_num);
  switch (uart_num) {
    case 0: Serial0.end(); break;
#if SOC_UART_NUM > 1
    case 1: Serial1.end(); break;
#endif
#if SOC_UART_NUM > 2
    case 2: Serial2.end(); break;
#endif
#if SOC_UART_NUM > 3
    case 3: Serial3.end(); break;
#endif
#if SOC_UART_NUM > 4
    case 4: Serial4.end(); break;
#endif
#if SOC_UART_NUM > 5
    case 5: Serial5.end(); break;
#endif
    default: log_e("hal_uart_notify_pins_detached: UART%d not handled!", uart_num); break;
  }
}
#endif

[nomakewan]

Sorry for the previous notif; hadn't noticed that the bit you had at the top of the test sketch was required for linking the application. I added it to my application software for now to test, and can confirm that the issue with pin 43 not working as TX indeed appears to be resolved! The upstream device successfully synchronizes and controls my downstream S3.

I really like these flags; it does exactly what we want (don't instantiate any default objects except for Serial on HWCDCSerial) and would save us that single Serial0.end() call in our main.cpp. I would love to see them implemented in a way that works around having to include the additional code in the user program!

Best of luck, and thank you for the swift response!

[SuGlider]

The issue seems related to some recent changes done to IDF that have added automatic UART pin management in order to detach and attach pins. It seems to conflict with the Arduino HAL level code that had to do that autoamtically.

Regrading the flags:

-DNO_GLOBAL_SERIAL ===> It will prevent automatic Serial, Serial0, ... Serial2 object declaration, and also many other functions and macro definition that depend on those object instanciation. If it is defined, all obejcts must be manually declared.

-DSerial=HWCDCSerial ==> Serial is just a macro definition in Arduino Core code that depends on using or not CDC and so on. Threfore if it is used, it must be associated to some "serialiazable" (USB, UART, File) obejct of a Stream/Printable class.

[nomakewan]

Right, with the -DNO_GLOBAL_SERIAL though surely there would be a way to prevent the linker error without adding the entire hal_uart_notify_pins_detached to the user program though, yes? Because we already manually declare all our serial objects in our application:

https://github.com/gpstar81/GPStar-proton-pack/blob/3181e42cfc7ef78f8c396522042e15ceb3a299a3/source/ProtonPack/include/Serial.h#L44-L46

So we actually have no use for Serial0, Serial1, etc. anyway.

[SuGlider]

with the -DNO_GLOBAL_SERIAL though surely there would be a way to prevent the linker error without adding the entire hal_uart_notify_pins_detached to the user program though, yes?

I'm afraid that it is necessary...
But you can just declare it "empty", like this:
extern "C" void hal_uart_notify_pins_detached(int uart_num) { }

It is only necessary to stop UART when all its pins are detached by the user, such as using them within other peripherals.

[nomakewan]

Just tried that empty declaration and it works perfectly in our application! Thank you again!

[SuGlider]

Just tried that empty declaration and it works perfectly in our application! Thank you again!

This linking error will be fixed for good with the PR #12412

[nomakewan]

Excellent news! Thank you once again for your diligence, I really do appreciate it.