stm32f4代码之w25q64驱动，spi普通读写及spi dma读写。spi普通读采用寄存器操作方式以及nop延时能够达到最大传输速率。-w25q64 stm32f4 code for the driver, spi and spi dma ordinary reader to read and write. spi register using ordinary read operation and nop delay to reach the maximum transfer rate.