sub WriteSpinData {
   
  my ($OUT_FH, $ref_data) = @_;
  my $frames_per_row = 65;

  for my $filename (sort keys %$ref_data ) {    
    my $basename = basename $filename;

    # create a list of major frames for the file
    my @majors = map  { $ref_data->{$filename}{$_} }
                 sort { $a <=> $b } keys %{ ref_data->{$filename} };

    for my $major ( @majors ) {

      # join all minor frames together
      my @minors = map  { $major->{$_} }
                   sort { $a <=> $b } # assuming  sorted
                   grep { /\d+/ }
                   keys %$major;

      # print them a row at a time
      while ( my @row = splice( @minors, 0, $frames_per_row ) ) {
        my $row_name = find_row_name( @row );
        my @data = map { @{$_}[3..17] } @row;
        print $OUT_FH join( q{,}, $row_name, @data ), "\n";
      }

    }
    print "$basename: " . @majors . " major frames.\n";
  }
}