Use an un-official community collaboration version of asn1c
1. It's no need to modify LTE-RRC's ASN.1 file for enabling option group feature in generate_asn1. 2. It's no need to patch the C header files generated from LTE-RRC/S1AP/X2AP's ASN.1 in fix_asn1. 3. It's no need to pre-process S1AP/X2AP's ASN.1 for enabling information object class feature by asn1tostruct.py. This commit requires an un-official version of asn1c which are collaboration of asn1c community members and `build_helper` is modified in this commit accordingly : https://github.com/brchiu/asn1c/tree/velichkov_s1ap_plus_option_group This asn1c can also convert ASN.1 of 5G NR RRC (38.331, v15.1.0) and generate C files with -findirect-choice command line option without tweaking ASN.1 file. Examples for how to use this asn1c for S1AP are in S1AP files, e.g. s1ap_eNB_nas_procedures.c and s1ap_eNB_handler.c. There is an modified openair-cn (based on tag 0.5.0) with this new asn1c at : https://github.com/brchiu/openair-cn/tree/new-asn1c Basic S1AP interaction and data transfer operation between OAI eNB and this modified openair-cn has been tested. Note: Community version of asn1c is keeping evolved to provide better usage.