说明：  stm32 iic库，单字节通信采用轮询方式，多字节采用dma67,相当稳定，是由别人的代码修改而成，使用上有些技巧，请查看源码注释
(stm32 iic library, single-byte communication by polling multi-byte adopt dma67, fairly stable modifications made by someone else' s code, some tips on the use, check out the source code comments)