DM9000_ISR
int_status = ior(db, DM9000_ISR); /* Got ISR */
iow(db, DM9000_ISR, int_status); /* Clear ISR status */
db->io_mode = ior(db, DM9000_ISR) >> 6; /* ISR bit7:6 keeps I/O mode */
iow(db, DM9000_ISR, ISR_CLR_STATUS); /* Clear interrupt status */