Can't make uart receive data

Mbed OS
1

Hi, I have a code written below. It has to send some data on my pc each 10 ms. Also, I want to send a single number back via the same uart. It works fine until I send anything, then it stops completely.

#include "mbed.h"
#include "rtos.h"
Serial pc(PA_2, PA_3);
EventQueue eventQueue;
volatile int pos;
void uartOut(){
    pc.printf("%i", pos);
}
void uartIn(){
    if(pc.readable()){
    pc.scanf("%i", &pos);
    }
}
int main() {
    pc.baud(115200);
    eventQueue.call_every(10, uartOut);
    eventQueue.call_every(10, uartIn);
    eventQueue.dispatch_forever();
}
2

Hi @lav522
What is the board you are using?
Could you confirm that PA_2 pin is in fact the SERIAL_TX pin, and that it is correctly configured?
Regards,
Mbed support
Ron

3

I’m using BlackBoard with STM32F407VET6 on it. It’s the right pin, i’ve also tried the other UART pins (PD5, PD6) and got the same behavior.

4

Sounds like scanf() is waiting for a newline. Are you sure you are sending a line ending character?

5

Yes, you were right about that, now, when i’m adding \n it doesn’t stop. But I have another problem: it doesn’t receive my messages each time, so I have to press “send” button 10-20 times until it gets it.

6

You don’t want to use scanf in a character interrupt. It’s better to use an interrupt handler that only takes a character and then process the buffer when characters are received. PC.readable only tells you that at least 1 character is available. scanf wants a full line with CRLF in it.
Grab characters via interrupt and then just process the buffer on a regular interval and you should be ok.

7

Guys, new information: program stops every time it goes to interrupt context.

void onCharReceived(){
        led2 = !led2;
}
int main() {
    pc.attach(&onCharReceived);

        while (1) {
            pc.putc(pc.getc());
   }
}

Once I send anything, it stops.

8

Ahoj,
ye, you can not use it like that. The serial interrupt flag was set but not cleaned. Maybe my old answer will help you to understand.

BR, Jan

9

Thank you so much! RawSerial solved the problem.