实现FPGA读取AD转换的数据，AD芯片我采用的是ADS7844，采用的是SPI通信方式-achieve the function of read the data from the AD transform chip.the communciation method is SPI.i have tested the code ,and it can work.

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

* This supports access to SPI devices using normal userspace I/O calls. * Note that while traditional UNIX/POSIX I/O semantics are half duplex, * and often mask message boundaries, full SPI support requires full duplex * transfers. There ar