anchor.diff:  
   buildPythonPackage rec {
     pname = "glasgow";
  -  version = "unstable-2019-08-31";
  -  realVersion = lib.substring 0 7 src.rev;
  +  version = "unstable-2019-09-28";
  +  # python setup.py --version
  +  realVersion = "0.1.dev1234+g${lib.substring 0 7 src.rev}";
   
     src = fetchFromGitHub {
       owner = "GlasgowEmbedded";
       repo = "Glasgow";
  -    rev = "21641a13c6a0daaf8618aff3c5bfffcb26ef6cca";
  -    sha256 = "1dpm1jmm4fg8xf17s6h9g5sc09gq8b6xq955sv2x11nrbqf98l4v";
  +    rev = "a1cc0333315847980806fd0330021c6de05c5395";
  +    sha256 = "0rdx7fymz828i73bc559sr67aikydz1m8s2a0i6c86gznh1s3cfk";
     };
   
  -  nativeBuildInputs = [ sdcc ];
  +  nativeBuildInputs = [ setuptools_scm sdcc ];
   
     propagatedBuildInputs = [
  +    setuptools
       nmigen
       fx2
       libusb1
  
positive.code: { lib
  , buildPythonPackage
  , fetchFromGitHub
  , sdcc
  , nmigen
  , fx2
  
negative.code:     crcmod
    ];
  
    preBuild = ''
      make -C firmware LIBFX2=${fx2}/share/libfx2
      cp firmware/glasgow.ihex software/glasgow
      cd software
      export SETUPTOOLS_SCM_PRETEND_VERSION="${realVersion}"
    '';
  
    # a couple failing tests and also installCheck tries to build_ext again
  