TxFreeThreshold
outb(PKT_BUF_SZ >> 8, ioaddr + TxFreeThreshold); /* Room for a packet. */
iowrite8(PKT_BUF_SZ>>8, ioaddr + TxFreeThreshold); /* Room for a packet. */
iowrite8(PKT_BUF_SZ>>8, ioaddr + TxFreeThreshold);