基于fpga verilog 语言和nios ii实现的spi模式下sd卡驱动，以及加入znfat文件系统的sd卡驱动，可读取sd卡内的文件。-Based on the language and under the fpga verilog realize spi mode nios ii sd card driver, and adding znfat sd card file system driver, you can read files sd card.