CH_FIFO_ENABLED
ch->ch_flags |= (CH_FIFO_ENABLED | CH_TX_FIFO_EMPTY | CH_TX_FIFO_LWM);
ch->ch_flags |= CH_FIFO_ENABLED;
if (!(ch->ch_flags & CH_FIFO_ENABLED))
if (!(ch->ch_flags & CH_FIFO_ENABLED)) {