TX_BD_TOTAL_PER_PAGE
&fp->tx_chain[TX_BD_TOTAL_PER_PAGE * j - 1].next_bd;
#define TX_BD_USABLE_PER_PAGE (TX_BD_TOTAL_PER_PAGE - 1)
#define TX_BD_TOTAL (TX_BD_TOTAL_PER_PAGE * TX_BD_NUM_PAGES)