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First of all, go to assignments -> settings -> compilation process settings and make sure that "run assembler during compilation" is ticked.
You can always manually run the assembler by going processing -> start -> assembler
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Yes , i have checked that option, assembler is working fine but there is one warning under EDA netlist writer
Warning (199027): Can't generate output files. Specify command-line options to generate output files, or update EDA tool settings using GUI or Tcl script.
i don't know how to fix this warning.