How can I tell what U(S)ART is used with setTx() and setRx() when more than one is possible?

[PerennialNovice]

Using for example STM32L4R5, setting serial Rx and Tx to PC11 and PC10
When I check in the datasheet, on those pins I have USART3 or UART4
PA3 and PA2 can be LPUART1 or USART2

How do I know what peripheral is beeing used?

Also, is there a difference in using setTx() and setRx() and defining a new HardwareSerial using HardwareSerial newSerial(Rx, Tx)?

[fpistm]

Hi @MasteringTheMess
You can find the information in the PeripheralPins.c, all possible value are referenced here:

Arduino_Core_STM32/variants/STM32L4xx/L4R5Z(G-I)T_L4R7ZIT_L4S5ZIT_L4S7ZIT/PeripheralPins.c

Lines 208 to 209 in 8f337e8

	{PA_2, LPUART1, STM_PIN_DATA(STM_MODE_AF_PP, GPIO_PULLUP, GPIO_AF8_LPUART1)},
	{PA_2_ALT1, USART2, STM_PIN_DATA(STM_MODE_AF_PP, GPIO_PULLUP, GPIO_AF7_USART2)},

To choose the right instance you can use the _ALTx notation.
Example to use USART2

mySerial.setTx(PA2_ALT1);
mySerial.setRx(PA3_ALT1);

while using:

mySerial.setTx(PA2);
mySerial.setRx(PA3);

will use LPUART1.

Note that the PeripheralPins.c reference the PinName (PY_n). Arduino API use the pin number (PYn).

[PerennialNovice]

Thanks!

...so, using the Arduino pin numbers will choose the first instance that is found in the PeripheralPins.c file?

[fpistm]

No. It takes the one specified by the pin number you used. If you use PA2 it uses LPUART1, if you use PA2_ALT1 it uses LPUART. I thought my answer was clear...

[PerennialNovice]

ok, so PA2 and PA_2 are the same and the Arduino API does not know about the ALT pins...

[fpistm]

PA2 is the pin number while PA_2 is a PinName ( combination of GPIO port and pin). PA2 is simply a define to a number (index) to be able to retrieve the correct PinName PA_2. PA2_ALT1 allows to retrieve PA_2_ALT1.

[PerennialNovice]

thanks a lot for explaining so patiently :)