DMA_TX_DESC_WRITE
HWRITE4(sc, DMA_TX_DESC_WRITE(ac->ac_chan), addr);
HWRITE4(sc, DMA_TX_DESC_WRITE(ac->ac_chan), addr >> 32);
HWRITE4(sc, DMA_TX_DESC_WRITE(ac->ac_chan), ac->ac_blksize);
HWRITE4(sc, DMA_TX_DESC_WRITE(ac->ac_chan), DMA_DESC_NOTIFY);