Correct use of HardwareSerial

[brightproject]

Good day @fpistm
I use this wonderful framework to build firmware for STM32F401/411.
For my application, I need to use the uBlox receiver GPS, which works over UART.
I allocated Serial for debugging, and UART2 for communication with MCU andGPS module.
The problem is using a third-party library to work with the UBX protocol.
My usual code.
Previously, this code always worked and I could use two or more serial ports for both input and output.

#define SERIAL_BAUD 115200
#define GNSS_BAUD 115200

HardwareSerial Serial2(USART2); // PA2(TX2), PA3(RX2)

void setup() 
{
  Serial.begin(SERIAL_BAUD);
  Serial2.begin(GNSS_BAUD);
}

void loop() {
Serial.println("Serial 1");
Serial2.println("Serial 2");

// if (Serial2.available() > 0)
// Serial.write(Serial2.read());
// Serial2.write(Serial.read());

}

My code for uBlox GPS:

#include <ubx.h>

#define SERIAL_BAUD 115200
#define GNSS_BAUD 115200

// #define USART2 Serial2

// extern HardwareSerial USART2;
HardwareSerial Serial2(USART2); // PA2(TX2), PA3(RX2)
// HardwareSerial Serial2(PA2, PA3);
// HardwareSerial& GPS = Serial2;

bfs::Ubx gnss(&Serial2);
//bfs::Ubx gnss(&GPS);

void setup() {
  /* Serial to display data */
  Serial.begin(SERIAL_BAUD);
  while(!Serial) {}
  gnss.Begin(GNSS_BAUD);
}

void loop() {

  delay(20);

  if(gnss.Read()) {
    Serial.print(gnss.fix());
    Serial.print("\t");
    Serial.print(gnss.num_sv());
    Serial.print("\t");
    Serial.print(gnss.lat_deg(), 6);
    Serial.print("\t");
    Serial.print(gnss.lon_deg(), 6);
    Serial.print("\t");
    Serial.print(gnss.alt_wgs84_m(), 2);
    Serial.print("\n");
  }
}

The code compiles without errors, but nothing is output to the serial port, I have some suspicions.

First, in the sketch I declare the HardwareSerial and pass only a pointer to the port serial to the UBX library.
But the library itself also creates an instance for working with the HardwareSerial and it seems to me that this is the reason for the serial ports not working.
https://github.com/bolderflight/ublox/blob/b472d38bca21cc37843a04b9422692edd5f5d6e2/src/ubx.h#L52
explicit Ubx(HardwareSerial* bus) : bus_(bus) {}
The difficulty is that the authors wrote the library mainly for the Teensy microcontroller.
And everything works on it without problems.
No matter how hard I tried to remove the HardwareSerial port declaration, I always got an error.
How can I correctly declare a HardwareSerial port so as not to rewrite the library?
I hope my explanations will not confuse you, because I myself am already quite confused.

[fpistm]

Hi @brightproject
As a first feedback, seems you used the same U(S)ART. By default Serial is mapped to USART2 for STM32F401:

Arduino_Core_STM32/variants/STM32F4xx/F401R(B-C-D-E)T/variant_generic.h

Lines 147 to 152 in 63d3096

	#ifndef PIN_SERIAL_RX
	#define PIN_SERIAL_RX PA3
	#endif
	#ifndef PIN_SERIAL_TX
	#define PIN_SERIAL_TX PA2
	#endif

So I guess here it is the first mistake.
For me the library does not instantiate HardwareSerial, you provide only a pointer to it.

[brightproject]

Thank you for your answer, but it seems to me that you did not quite understand me, and you did not ask any questions🙂
Below I have simplified the code to make it more clear.
By default, in STM32 you can only use serial port 1 and we designate its Serial, if we want to use serial 2, then we just don’t declare it.
You must specify the use of HardwareSerial.
If you do not specify this explicitly, then calling the code
Serial2.Begin(SERIAL2_BAUD );
in the setup section will lead to a compilation error, which is logical.

#define SERIAL_BAUD 115200
#define SERIAL2_BAUD 115200

HardwareSerial Serial2(USART2); 

void setup() {
  Serial.begin(SERIAL_BAUD);
  Serial2.Begin(SERIAL2_BAUD );
}

void loop() {
// somethings
}

Moving on, I have a third-party library, which inside itself has an algorithm for determining the HardwareSerial.
The library input must be supplied with the name of the port serial to be used.
But, according to the description above, I cannot submit just Serial2 as input to the library, because I need to declare it first through
HardwareSerial Serial2(USART2);
And it turns out that I declare the HardwareSerial twice - which is generally not true and possible, which is why I have problems with the library.

void Ubx::Config(HardwareSerial* bus) {
  bus_ = bus;
}

Specify this code in the library
USART2.Begin(SERIAL2_BAUD )
This is also not possible, there will be a compilation error.

[fpistm]

By default, in STM32 you can only use serial port 1 and we designate its Serial

No. Serial is simply an alias to the specified Serialx defined in the variant.
Ex for generic F401RB:

Arduino_Core_STM32/variants/STM32F4xx/F401R(B-C-D-E)T/variant_generic.h

Lines 140 to 152 in c83db2e

	// UART Definitions
	#ifndef SERIAL_UART_INSTANCE
	#define SERIAL_UART_INSTANCE 2
	#endif
	// Default pin used for generic 'Serial' instance
	// Mandatory for Firmata
	#ifndef PIN_SERIAL_RX
	#define PIN_SERIAL_RX PA3
	#endif
	#ifndef PIN_SERIAL_TX
	#define PIN_SERIAL_TX PA2
	#endif

So Serial is Serial1.

But for Generic F412ZG:

Arduino_Core_STM32/variants/STM32F4xx/F412Z(E-G)(J-T)/variant_generic.h

Lines 228 to 240 in c83db2e

	// UART Definitions
	#ifndef SERIAL_UART_INSTANCE
	#define SERIAL_UART_INSTANCE 2
	#endif
	// Default pin used for generic 'Serial' instance
	// Mandatory for Firmata
	#ifndef PIN_SERIAL_RX
	#define PIN_SERIAL_RX PA3
	#endif
	#ifndef PIN_SERIAL_TX
	#define PIN_SERIAL_TX PA2
	#endif

Serial is Serial2

I advise you read the wiki:
https://github.com/stm32duino/Arduino_Core_STM32/wiki/API#hardwareserial

As stated your first code uses the same Serial instance. Which target you select? Generic STM32F401RB ? other?

And it turns out that I declare the HardwareSerial twice - which is generally not true and possible, which is why I have problems with the library.

void Ubx::Config(HardwareSerial* bus) {
  bus_ = bus;
}

No it is a pointer the third library do not "declare HardwareSerial twice". Several library worked like this to ease usage. Maybe a reference would be better but it is an other discussion.
It is well documented in the library you used:
https://github.com/bolderflight/ublox?tab=readme-ov-file#methods

#define SERIAL_BAUD 115200
#define SERIAL2_BAUD 115200

HardwareSerial Serial2(USART2);

void setup() {
Serial.begin(SERIAL_BAUD);
Serial2.Begin(SERIAL2_BAUD );
}

void loop() {
// somethings
}

Here this code is not correct for generic STM32F401RB as it is not Begin but begin.
Then after correct this the error is clear:
core/core.a(HardwareSerial.cpp.o):(.bss.Serial2+0x0): multiple definition of Serial2'; which is normal, as statedSerialisSerial2`.

Specify this code in the library
USART2.Begin(SERIAL2_BAUD )
This is also not possible, there will be a compilation error.

This is normal USART2 name is an CMSIS device definition:
https://github.com/stm32duino/Arduino_Core_STM32/blob/c83db2e4f6b4b8d3bbedce67d2156a58023bc432/system/Drivers/CMSIS/Device/ST/STM32F4xx/Include/stm32f401xe.h#L759C1-L759C1

it seems you don't understand what you do.
So if you use the generic STM32F401RE (same for Nucleo), Serial is Serial2 so no need to redefine it.
If you used Serial for "debug", nothing to do.
Then you have to declare and use a new instance for your GPS, ex USART1 using PA9/PA10.
HardwareSerial Serial1(USART1);
or
HardwareSerial Serial1(PA10, PA9);
or you can also use an custom name:
HardwareSerial myGPS(PA10, PA9);

So, a correct code would be;

#include "ubx.h"

#define SERIAL_BAUD 115200
#define GNSS_BAUD 921600

HardwareSerial myGNSS(PA10, PA9);

/* Ublox object, GNSS on USART1 pins PA9/PA10 name myGNSS */
bfs::Ubx gnss(&myGNSS);

void setup() {
  Serial.begin(SERIAL_BAUD);
  // Ublox instance will call begin of the myGNSS instance.
  // myGNSS.begin(GNSS_BAUD);
  gnss.Begin(GNSS_BAUD);
}

void loop() {
  // somethings
}