说明：  在stm32单片机上，用IO口的上升沿和下降沿中断设计的I2C从机代码。测试通过。所有过程用状态机来控制，没有cpu空延时。 核心代码和单片机相关代码分开，方便移植。 主要用在项目验证和学习交流！
(On stm32 microcontroller, with rising and falling IO port interrupt design of I2C slave code. The test. All the process is controlled by a state machine, no cpu empty delay. Microcontroller core code and related code separate, easy to transplant. Mainly used in the project validation and exchange of learning!)