此函数把SPI的读写功能集成在一块，传递的val既是向SPI写的数据，也是从SPI读取的数据，只需要在执行读或写之前把MCU的I/O脚设置成相应的输出或输入即可。-This function of the SPI read and write functions integrated in one, passing val both written to the SPI data is read from the SPI data, only need to perform a read or write before the MCU' s I/O pin is set to the corresponding output or typing.