You may get this error with NC Verilog when you are using the following command to simulate:
$ apex20ke_atoms.v
The simulator assumes all files contain top-level modules and initiates the upcore module from the apex20ke_atoms.v file and reports the missing .dat and .cfg files.
To avoid this error you will need to use the following command with the -v switch that instructs the tool to only initiate modules that are called by the design:
$ -v apex20ke_atoms.v
Note: Along with the above error you may also get the following warning message:
“ error: open failed on file ‘slavememory.cfg.dat’ error: open failed on file ‘mastercommands.dat’ ncsim: *W,VFOPTW: File output.dat being opened by Initial stmt (file:../include/apex20ke_atoms.v, line: 4447 in worklib.apex20ke_upcore [module]) has been opened earlier.”