TXCFG_FIFO_UNIT
lp->tx_drain_threshold = ROUNDUP2(dp->txthr, TXCFG_FIFO_UNIT);
TXFIFOSIZE - lp->tx_drain_threshold - TXCFG_FIFO_UNIT;
ASSERT(lp->tx_drain_threshold < 64*TXCFG_FIFO_UNIT);
ASSERT(lp->tx_fill_threshold < 64*TXCFG_FIFO_UNIT);
txcfg |= ((lp->tx_fill_threshold/TXCFG_FIFO_UNIT) << TXCFG_FLTH_SHIFT)
| (lp->tx_drain_threshold/TXCFG_FIFO_UNIT);