dvbt_calc_snr
ret = dvbt_calc_snr(tnr_dmd, reg_value, snr);
ret = dvbt_calc_snr(tnr_dmd, reg_value, snr_main);
ret = dvbt_calc_snr(tnr_dmd->diver_sub, reg_value, snr_sub);
return dvbt_calc_snr(tnr_dmd, reg_value_sum, snr);