完整SD控制器！支持文件系统。

代码说明：

32-bit Wishbone Interface • DMA • Buffer Descriptor • Compliant with SD Host Controller Spec version 2.0 • Support SD 4-bit mode • Interrupt-on-completion of Data and Command transmission • Write/Read FIFO with variable size • Internal implementation of CRC16 for data lines and CRC7 for command line Wishbine 总线使用。完整的SD卡控制器，支持文件系统，高速传输。