STM32F407系列单片机多串口收发测试代码，串口1，串口2，串口3，串口4，同时发送数据，然后从串口5，转发从串口1，串口2，串口3，串口4接受到的数据。-Serial port 2, serial port 3, serial port 4, and send data, and then the serial port 5, forwarded the serial port 1, serial port 2, serial port 3, the serial port 4 to