MAILBOX_RCVRET_CON_IDX_0
tw32_mailbox2(MAILBOX_RCVRET_CON_IDX_0 + TG3_64BIT_REG_LOW, 0);
tw32_mailbox2(MAILBOX_RCVRET_CON_IDX_0 + TG3_64BIT_REG_LOW, tp->rx_rcb_ptr);