kssb < 16 or we cannot do reestablishment: add assert in DU

ci-scripts/conf_files/gnb.sa.band78.51prb.usrpb200.conf

@@ -30,7 +30,7 @@ gNBs =
       absoluteFrequencySSB                                             = 620736;
       dl_frequencyBand                                                 = 78;
       # this is 3300.30 MHz
-      dl_absoluteFrequencyPointA                                       = 620020;
+      dl_absoluteFrequencyPointA                                       = 620052;
       #scs-SpecificCarrierList
         dl_offstToCarrier                                              = 0;
 # subcarrierSpacing

openair2/LAYER2/NR_MAC_gNB/config.c

@@ -332,6 +332,12 @@ static void config_common(gNB_MAC_INST *nrmac, int pdsch_AntennaPorts, int pusch
    cfg->ssb_table.ssb_subcarrier_offset.value =
        get_ssb_subcarrier_offset(*scc->downlinkConfigCommon->frequencyInfoDL->absoluteFrequencySSB,
                                  scc->downlinkConfigCommon->frequencyInfoDL->absoluteFrequencyPointA);
+   AssertFatal(cfg->ssb_table.ssb_subcarrier_offset.value < 16,
+               "cannot handle ssb_subcarrier_offset %d resulting from Point A %ld SSB %ld: please increase dl_absoluteFrequencyPointA "
+               "in the config by 16\n",
+               cfg->ssb_table.ssb_subcarrier_offset.value,
+               scc->downlinkConfigCommon->frequencyInfoDL->absoluteFrequencyPointA,
+               *scc->downlinkConfigCommon->frequencyInfoDL->absoluteFrequencySSB);
    cfg->ssb_table.ssb_subcarrier_offset.tl.tag = NFAPI_NR_CONFIG_SSB_SUBCARRIER_OFFSET_TAG;
    cfg->num_tlv++;