DMA_SCREG
DMA->dma_mode = DMA_SCREG | (mode & DMA_WRBIT);
DMA->dma_mode = FDC_CS | DMA_SCREG;
st_dmacomm(DMA_FDC | DMA_SCREG, 1);
st_dmacomm(DMA_WRBIT | DMA_FDC | DMA_SCREG, 1);