stm32F103c8t6通过串口uart1连接有人4g模块7s4完成mqtt客户端协议的简单移植。初步测试通过。完成连接、订阅主题、发布主题、心跳的初步移植。(Stm32f103c8t6 is connected to 4G module 7s4 through uart1 to complete the simple transplantation of mqtt client protocol. The preliminary test passed. Complete the initi