reg_to_16bits
s_tmp = reg_to_16bits(0xff - st->signal_level);
c_tmp = reg_to_16bits(0xff - st->signal_sn);
c_tmp = reg_to_16bits((0xff - st->signal_sn - 0xa1) * 3);
s_tmp = reg_to_16bits(st->signal_level);
c_tmp = reg_to_16bits(st->signal_sn);