CHAN_CMDPTR
dbdma_write_reg(chan, CHAN_CMDPTR, cmd);
chan->sc_saved_regs[0] = dbdma_read_reg(chan, CHAN_CMDPTR);
dbdma_write_reg(chan, CHAN_CMDPTR, chan->sc_saved_regs[0]);
dbdma_write_reg(channel, CHAN_CMDPTR, channel->sc_slots_pa);