My external C function called by stateflow is not recognized during code generation.

I added the file name in the custom code as well as simulation target. But I get the following error message while generating code: Microsoft (R) Program Maintenance Utility Version 10.00.30319.01 Copyright (C) Microsoft Corporation. All rights reserved.

    ### Compiling BusAtruProtection.c
      cl   -c -DCRTAPI1=_cdecl -DCRTAPI2=_cdecl -nologo -GS -D_AMD64_=1 -DWIN64 -D_WIN64  -DWIN32 -D_WIN32 -W4 -D_WINNT -D_WIN32_WINNT=0x0500 -DNTDDI_VERSION=0x05000000 -D_WIN32_IE=0x0500 -DWINVER=0x0500  -D_MT -D_DLL -MD  -D_CRT_SECURE_NO_WARNINGS  -DSLMSG_ALLOW_SYSTEM_ALLOC  /Od /Oy- /DNDEBUG -DMODEL=BusAtruProtection -DNUMST=2 -DNCSTATES=0  -DMAT_FILE=0 -DINTEGER_CODE=0  -DONESTEPFCN=0 -DTERMFCN=1  -DHAVESTDIO -DMULTI_INSTANCE_CODE=0  -DCLASSIC_INTERFACE=0  -DALLOCATIONFCN=0   -DMDL_REF_SIM_TGT=1 -DENABLE_SLEXEC_SSBRIDGE=11   BusAtruProtection.c
    BusAtruProtection.c
    BusAtruProtection.c(906) : warning C4013: 'InitAtruVoltageBuffer' undefined; assuming extern returning int
    BusAtruProtection.c(911) : warning C4013: 'UpdateAtruDiffVoltage' undefined; assuming extern returning int
    BusAtruProtection.c(935) : warning C4127: conditional expression is constant
    ### Compiling BusAtruProtection_capi.c
      cl   -c -DCRTAPI1=_cdecl -DCRTAPI2=_cdecl -nologo -GS -D_AMD64_=1 -DWIN64 -D_WIN64  -DWIN32 -D_WIN32 -W4 -D_WINNT -D_WIN32_WINNT=0x0500 -DNTDDI_VERSION=0x05000000 -D_WIN32_IE=0x0500 -DWINVER=0x0500  -D_MT -D_DLL -MD  -D_CRT_SECURE_NO_WARNINGS  -DSLMSG_ALLOW_SYSTEM_ALLOC  /Od /Oy- /DNDEBUG -DMODEL=BusAtruProtection -DNUMST=2 -DNCSTATES=0  -DMAT_FILE=0 -DINTEGER_CODE=0  -DONESTEPFCN=0 -DTERMFCN=1  -DHAVESTDIO -DMULTI_INSTANCE_CODE=0  -DCLASSIC_INTERFACE=0  -DALLOCATIONFCN=0   -DMDL_REF_SIM_TGT=1 -DENABLE_SLEXEC_SSBRIDGE=11   BusAtruProtection_capi.c
    BusAtruProtection_capi.c
      Z:\sys\perl\win32\bin\perl Z:\rtw\c\tools\mkvc_lnk.pl BusAtruProtection.lnk BusAtruProtection.obj BusAtruProtection_capi.obj ConditionFixedTD.obj ConditionFixedTDwithInhibit.obj OneshotTD_Falling_Edge.obj OneshotTD_Rising_Edge.obj OverProtectionWithInhibitAndCondition.obj UnderProtectionWithInhibitAndCondition.obj  
      link -lib /OUT:BusAtruProtectionlib.lib @BusAtruProtection.lnk 
    Microsoft (R) Library Manager Version 10.00.30319.01
    Copyright (C) Microsoft Corporation.  All rights reserved.

    BusAtruProtection.obj 
    BusAtruProtection_capi.obj 
    ConditionFixedTD.obj 
    ConditionFixedTDwithInhibit.obj 
    OneshotTD_Falling_Edge.obj 
    OneshotTD_Rising_Edge.obj 
    OverProtectionWithInhibitAndCondition.obj 
    UnderProtectionWithInhibitAndCondition.obj 
     Created static library BusAtruProtectionlib.lib
      Z:\bin\mex -win64  OPTIMFLAGS="/Od /Oy- /DNDEBUG" -DMDL_REF_SIM_TGT=1 -DENABLE_SLEXEC_SSBRIDGE=11 -f "C:\Users\maddalvx\AppData\Roaming\MathWorks\MATLAB\R2016a\mex_C_win64.xml"  BusAtruProtection_msf.c BusAtruProtectionlib.lib @BusAtruProtection_ref.rsp ..\..\..\slprj\sim\_sharedutils\rtwshared.lib   Z:\extern\lib\win64\microsoft\libfixedpoint.lib Z:\lib\win64\libmwipp.lib Z:\extern\lib\win64\microsoft\libmwslexec_simbridge.lib Z:\extern\lib\win64\microsoft\libmwmathutil.lib Z:\extern\lib\win64\microsoft\libmwsimulink.lib Z:\extern\lib\win64\microsoft\libmwsl_fileio.lib Z:\extern\lib\win64\microsoft\libmwsl_iofile.lib Z:\extern\lib\win64\microsoft\libmwsigstream.lib Z:\extern\lib\win64\microsoft\libmwsl_log_load_blocks.lib Z:\extern\lib\win64\microsoft\libmwsl_AsyncioQueue.lib Z:\extern\lib\win64\microsoft\libmwcoder_ToAsyncQueueTgtAppSvc.lib Z:\extern\lib\win64\microsoft\sf_runtime.lib -outdir ..\..\..
    Building with 'Microsoft Windows SDK 7.1 (C)'.
       Creating library C:\Matlab\AGE21011E_2016a\Model\BusAtruProtection_msf.lib and object C:\Matlab\AGE21011E_2016a\Model\BusAtruProtection_msf.exp
    BusAtruProtectionlib.lib(BusAtruProtection.obj) : error LNK2019: unresolved external symbol UpdateAtruDiffVoltage referenced in function joeylifcnq
    BusAtruProtectionlib.lib(BusAtruProtection.obj) : error LNK2019: unresolved external symbol InitAtruVoltageBuffer referenced in function joeylifcnq
    C:\Matlab\AGE21011E_2016a\Model\BusAtruProtection_msf.mexw64 : fatal error LNK1120: 2 unresolved externals

    NMAKE : fatal error U1077: 'Z:\bin\mex.BAT' : return code '0xffffffff'
    Stop.

[Abhi Sundararaman]

Are there any header files your .c file depends on? The errors you're getting suggest that something was not properly defined.

BusAtruProtectionlib.lib(BusAtruProtection.obj) : error LNK2019: unresolved external symbol UpdateAtruDiffVoltage referenced in function joeylifcnq
BusAtruProtectionlib.lib(BusAtruProtection.obj) : error LNK2019: unresolved external symbol InitAtruVoltageBuffer referenced in function joeylifcnq

The "unresolved external symbol" error suggests that these variables "UpdateAtruDiffVoltage" and "InitAtruVoltageBuffer" are not defined in the right place. Perhaps these need to come from a header file.