The function printf does not print anything on the console

Mbed OS
1

Hi all,

Recently, the function printf does not print any data to the console anymore. I did not face this issue before. I’ve read the threads with similar problems on this forum. However, not any solution worked for me. For example, I’ve added a ‘\n’ character at the end of the string, but this didn’t solve the problem.

Any ideas what can fix this problem? Thanks in advance!

Greetings,
Tom

2

Please share some code…

3

The code is shown below. When I run this code, an “empty” character is being printed in the console.

#include "mbed.h"

int main()
{
    printf("Hello World\n");

    while(1) {

    }

    return 0;
}
4

Ahoj,

Maybe it is related to a specific hardware or version of the Mbed OS or tools.
So what a version of MbedOS, a board and tools you use?

For me that printf working well on the MbedOS 6.2.1, Nucleo-F429ZI and Online Compiler.

BR, Jan

1 Like
5

We’re using the Mbed OS 6 version, in combination with Mbed Studio. The microcontroller that we’re using is NUCLEO-F411RE.

6

I had the same problem with another board and added this code below #include “mbed.h” and it then worked:

    // Create a BufferedSerial object to be used by the system 
    // Check that the USBTX and USBRX are correctly defined in target pinnames files or define yourself
   //  Insert the baud rate you want to use
    static BufferedSerial serial_port(USBTX, USBRX, 115200);

    FileHandle *mbed::mbed_override_console(int fd)
    {
        return &serial_port;
    }
1 Like
7

thats strange, a printf() should always work. If the baudrate does not match, you can also set it in the mbed_app.json:

    "target_overrides": {
        "*": {
            "platform.stdio-baud-rate": 115200,
            "platform.stdio-convert-newlines": true
        }

The STDIO_UART_TX/RX can be also remapped in the mbed_app.json, but the defaults work for the USB VCOM. Unless you have modified the solder jumpers on the Nucleo, the VCOM can be disconnected.

    // STDIO for console print
#ifdef MBED_CONF_TARGET_STDIO_UART_TX
    STDIO_UART_TX = MBED_CONF_TARGET_STDIO_UART_TX,
#else
    STDIO_UART_TX = PA_2,
#endif
#ifdef MBED_CONF_TARGET_STDIO_UART_RX
    STDIO_UART_RX = MBED_CONF_TARGET_STDIO_UART_RX,
#else
    STDIO_UART_RX = PA_3,
#endif

also PA_2 and PA_3 must not be connected to other hardware.

8

Yeah, I had the same problem. The ST default is 9600,8,N,1 and the mbed studio defaults are 115200,8,N,1 - just change the baud rate drop down for your board’s serial terminal to 9600 and it works fine.

1 Like