Arduino for STM32

ok , I will try something different :
1) instead of configure the two pins , for exemple : HardwareSerial Serial1(PA10, PA9);
just configure the Tx pin : HardwareSerial Serial1(PA9);
this will configure USART1 as half-duplex single wire mode , on PA9 = Tx pin ; at this point , PA9 is high Z , so ...

Hi fpiSTM , thanks !
I have tried to to declare first the the Rx and Tx pins , as STM32duino wants , and then make the Tx pin an input ; this works , but for a short moment , the Tx pin will be OUTPUT : HIGH , in conflict with the output of the device it is connected to , so this is not an option ...

STM32 , from the beginning , can do Rx or Tx alone , and the other pin can be used for another purpose
( I have being playing with STM32 a looong time before STM32duino )
some of the features of the USARTs (from the reference manual of your G431, a very interesting document ! ) :
• Separate enable ...

what I want to do , all USARTs Rx only :
USART3 Rx = PB11
LPUART1 Rx = PB10
USART2 Rx = PA15
USART1 Rx = PA10
UART4 Rx = PC11

oh yes , sorry , you have pointed the right thing :
the sketch with USART3 works , printing the registers to be sure :
USART3->CR1 : 45
LPUART1->CR1 : 0
my problem is actually that I only want the USART to work as a receiver ; Tx pin will be used for another task
so if I declare :
HardwareSerial ...

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Hi ,
I am trying make these USARTs to work , using the API , it doesn't , so for for exemple , USART1 :
- before the setup :
// setting PA10 as USART1 Rx : might be correct , according the DS , the RM , and the variant file
HardwareSerial Serial1(PA_10);
- in the setup :
Serial1.begin(250000 ...

yes , I have put the ISR in RAM , but I have no idea of the code between the trigger event and the ISR start
the speed is 133MHz , so the number of cycles is just 17-18
back to STM32 , I wonder if we can put ISRs (or other critical functions) in RAM , in order to make it faster ; I never done it ...

I remember , I got 200ns with PI PICO (which is ARM , too) ...

Is there an easy way to synchronize writes to GPIOs on two different ports so they happen at the same time?
unless in some highly-specialized cases, the answer is no.
two ways that I can think of:
1. you can use timer output compares to output up to 4 pin states. those OC pins can be on ...