Adafruit Feather STM32F405: undefined reference to Serial1

[zfields]

Describe the bug
The UART for the variant is misconfigured and Serial1 does NOT identify the Rx/Tx pins of the Adafruit Feather STM32F405.

Instead, Serial3 identifies Rx/Tx, as configured in the peripheral pins file, and targeted in the variant file.

#ifndef SERIAL_UART_INSTANCE
  #define SERIAL_UART_INSTANCE  3
#endif

Serial1 is the common interface for the Rx/Tx pins on Adafruit Feather boards. This can be validated by looking at the bottom of the variant header.

// SERIAL_PORT_HARDWARE       Hardware serial port, physical RX & TX pins.
...
#ifndef SERIAL_PORT_HARDWARE
  #define SERIAL_PORT_HARDWARE  Serial1
#endif

Not only is this unintuitive, but this breaks the portability of software between disparate Feather MCUs.

To Reproduce

Hardware:

• Adafruit Feather STM32F405
• FTDI cable

Firmware:

#define REPRO_ON_SERIAL 0

#if REPRO_ON_SERIAL == 0
  HardwareSerial txRxSerial(PIN_SERIAL_RX,PIN_SERIAL_TX);
#elif REPRO_ON_SERIAL == 1
  #define txRxSerial Serial1
#elif REPRO_ON_SERIAL == 2
  #define txRxSerial Serial2
#elif REPRO_ON_SERIAL == 3
  #define txRxSerial Serial3
#else
  #error "Unknown Repro Mode"
#endif

void setup (void) {
  txRxSerial.begin(115200);
  const size_t usb_timeout_ms = 3000;
  for (const size_t start_ms = millis(); !txRxSerial && (millis() - start_ms) < usb_timeout_ms;);
}

void loop (void) {
  txRxSerial.println("Hello, stm32duino!");
  ::delay(5000);
}

Steps to reproduce the behavior:

1. Set REPRO_ON_SERIAL to the desired SerialX object to test.
2. Open Serial Monitor
3. See error

Expected behavior

• When REPRO_ON_SERIAL is either 0 or 3, then the sketch will write "Hello, stm32duino!" on the Rx/Tx pins.
• When REPRO_ON_SERIAL is either 1 or 2, then the sketch will fail to compile.

Screenshots
If applicable, add screenshots to help explain your problem.

Desktop (please complete the following information):

• OS: Linux (Pop!_OS)
• Arduino IDE version: 1.8.19
• STM32 core version: 2.5.0
• Tools menu settings if not the default:
  • U(S)ART support: Enabled (generic 'Serial')
  • USB support (if available): CDC (generic 'Serial' supercede U(S)ART)
  • USB speed (if available): Low/Full Speed
  • Optimize: Debug (-Og)
  • Debug symbols and core logs: Symbols Enabled (-g)
  • C Runtime Library: Newlib Nano (default)
• Upload method: SWD

Board (please complete the following information):

• Name: Adafruit Feather STM32F405

Additional context

I noticed something else strange about the configuration while I was looking through it. You specify the RX pin for UART2 in the configuration, but not the TX pin:
https://github.com/stm32duino/Arduino_Core_STM32/blob/main/variants/STM32F4xx/F405RGT_F415RGT/PeripheralPins_FEATHER_F405.c#L175

[fpistm]

Hi @zfields
OK, will update to this:

  #ifndef SERIAL_PORT_HARDWARE
    #define SERIAL_PORT_HARDWARE  Serial3
  #endif

About

• When REPRO_ON_SERIAL is either 1 or 2, then the sketch will fail to compile.

This is normal, only one default Serialx is instantiate and mapped to Serial. Up to you to instantiate Serial1 and Serial2.
See https://github.com/stm32duino/Arduino_Core_STM32/wiki/API#hardwareserial

About UART2, yes, probably PA2 was commented because it is not connected. I will comment also PA3.