conflicting declaration 'arduino::HardwareSerial Serial1' #3033

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1. fpistm

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   Aymane-ST

   on Jul 25, 2026
2. fpistm commented on Jul 25, 2026

   

   fpistm

   on Jul 25, 2026

   Member

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   Hi @acronis2000
   3.0.0 release deployed the ArduinoCore-API.
   HardwareSerial has been renamed Uart.

   That's why major release number changed. See #2879.

   👍React with 👍2Reacted by acronis2000 and Aymane-ST
3. fpistm

   added

   invalidThis doesn't seem rightThis doesn't seem right

   arduino compatibility

   on Jul 25, 2026
4. whcir911 commented on Aug 6, 2026

   

   whcir911

   on Aug 6, 2026

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   Could you please show the proper syntax to use?

   👍React with 👍1Reacted by Aymane-ST
5. Aymane-ST commented on Aug 6, 2026

   

   Aymane-ST

   on Aug 6, 2026

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   Could you please show the proper syntax to use?

   Hi ! Version 3.0.0 throws an error

   ` #define Serial1_RX PA10 // Serial1 RX #define Serial1_TX PA9 // Serial1 TX

   HardwareSerial Serial1(Serial1_RX, Serial1_TX);

   void setup() { // put your setup code here, to run once: }

   void loop() { // put your main code here, to run repeatedly: }

   C:\Users\Admin\AppData\Local\Temp.arduinoIDE-unsaved2026625-8432-6liyya.ubz86\sketch_jul25a\sketch_jul25a.ino:4:16: error: conflicting declaration 'arduino::HardwareSerial Serial1' 4 | HardwareSerial Serial1(Serial1_RX, Serial1_TX); | ^~~~~~~ In file included from C:\Users\Admin\AppData\Local\Arduino15\packages\STMicroelectronics\hardware\stm32\3.0.0\cores\arduino/WSerial.h:5, from C:\Users\Admin\AppData\Local\Arduino15\packages\STMicroelectronics\hardware\stm32\3.0.0\cores\arduino/wiring.h:103, from C:\Users\Admin\AppData\Local\Arduino15\packages\STMicroelectronics\hardware\stm32\3.0.0\cores\arduino/Arduino.h:37, from C:\Users\Admin\AppData\Local\arduino\sketches\870FFC002468014B87DE5543024610EC\sketch\sketch_jul25a.ino.cpp:1: C:\Users\Admin\AppData\Local\Arduino15\packages\STMicroelectronics\hardware\stm32\3.0.0\cores\arduino/Serial.h:226:15: note: previous declaration as 'Uart Serial1' 226 | extern Uart Serial1; | ^~~~~~~ exit status 1

   Compilation error: conflicting declaration 'arduino::HardwareSerial Serial1' `

   Hi,

   The issue is that since 3.0.0 (see 2d23c7c), the stm32duino concrete serial class is now Uart instead of HardwareSerial.

   So this old syntax is no longer valid:

   HardwareSerial Serial1(Serial1_RX, Serial1_TX);

   It should now be:

   Uart Serial1(Serial1_RX, Serial1_TX);

   So the migration is basically:

   HardwareSerial -> Uart

   Thanks.

   👍React with 👍1Reacted by Frederic Pillon
6. fpistm

   closed this as completedon Aug 6, 2026