BCM2835_SPI_FIFO
byte = bcm2835_rd(bs, BCM2835_SPI_FIFO);
bcm2835_wr(bs, BCM2835_SPI_FIFO, byte);
val = bcm2835_rd(bs, BCM2835_SPI_FIFO);
bcm2835_wr(bs, BCM2835_SPI_FIFO, val);
val = bcm2835_rd(bs, BCM2835_SPI_FIFO);
bcm2835_wr(bs, BCM2835_SPI_FIFO, val);
slave_config.dst_addr = (u32)(dma_reg_base + BCM2835_SPI_FIFO);
slave_config.src_addr = (u32)(dma_reg_base + BCM2835_SPI_FIFO);