COMPLETE_DMA_SCB_TAIL
ahd_outw(ahd, COMPLETE_DMA_SCB_TAIL, scbid);
tail = ahd_inw(ahd, COMPLETE_DMA_SCB_TAIL);
ahd_outw(ahd, COMPLETE_DMA_SCB_TAIL, scbid);
ahd_outw(ahd, COMPLETE_DMA_SCB_TAIL, SCB_LIST_NULL);
ahd_outw(ahd, COMPLETE_DMA_SCB_TAIL, SCB_LIST_NULL);