DMA2_MODE
outb(DMA2_MODE, DMA37MD_CASCADE | (chan & 3));
outb(DMA2_MODE, DMA37MD_AUTO|DMA37MD_WRITE|(chan&3));
outb(DMA2_MODE, DMA37MD_AUTO|DMA37MD_READ|(chan&3));
outb(DMA2_MODE, DMA37MD_SINGLE|DMA37MD_WRITE|(chan&3));
outb(DMA2_MODE, DMA37MD_SINGLE|DMA37MD_READ|(chan&3));