WAITING_TID_HEAD
scbid = ahd_inw(ahd, WAITING_TID_HEAD);
waiting_h = ahd_inw(ahd, WAITING_TID_HEAD);
ahd_outw(ahd, WAITING_TID_HEAD, scbid);
ahd_outw(ahd, WAITING_TID_HEAD, SCB_LIST_NULL);
tid_next = ahd_inw(ahd, WAITING_TID_HEAD);
ahd_outw(ahd, WAITING_TID_HEAD, tid_next);
ahd_outw(ahd, WAITING_TID_HEAD, tid_cur);