RLDA_CYLSHFT
da |= ((cn - rc->rc_cyl) << RLDA_CYLSHFT) | RLDA_DIR;
da |= ((rc->rc_cyl - cn) << RLDA_CYLSHFT);
RL_WREG(RL_DA, (cn << RLDA_CYLSHFT) | (tn ? RLDA_HSRW : 0) | (sn << 1));