printf_to_uart

Send printf via UART on a STM32 MCU

How to send printf via UART

1. Override _write function

A UART write function to call from printf needs to be defined in syscalls.cpp

extern int _writeUart( char *ptr, int len );

The UART write is called from the system _write function

int _write(char *ptr, int len ) {
  return _writeUart(ptr, len);
}

2. Redirect _write output to UART

In the main.cpp the UART connection and the write Function need to be implemented

UART_HandleTypeDef huart3;

The printf function will call the write function that will send the data via USB to a Serial Monitor ()moserial

extern "C" {
  int _writeUart( char *ptr, int len )
  {
      HAL_UART_Transmit(&huart3, (uint8_t*) ptr, len, 0xFFFF);
      return 0;
  }
}

To receive messages you can use e.g. grabserial (see utils/GrabSerial.sh)

3. My printf isn't working, why?

• The correct port is /dev/ttyACM0
• Always end your printf with a linebreak (\n).
• Printf needs quite a bit of memory, make sure the executing thread has a big enough stack size.