说明：  与GPRS模块通讯需要使用串口，如果只需要发送短信，打电话那么只需要半双工就可以了。该源码中包含有对STM32串口的调用
(Communication module with GPRS need to use the serial port, if only to send text messages, phone calls then only half-duplex on it. The source code contains the serial port of call on the STM32)