diff --git a/scripts/generate_fill.py b/scripts/generate_fill.py
index 6b4cbcd..97e8141 100755
--- a/scripts/generate_fill.py
+++ b/scripts/generate_fill.py
@@ -1,4 +1,4 @@
-#!/bin/env python3
+#!/usr/bin/env python3
 # SPDX-FileCopyrightText: 2020 Efabless Corporation
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
@@ -17,7 +17,7 @@
 #
 # generate_fill.py ---
 #
-#    Run the fill generation on the caravel top level.
+#    Run the fill generation on a layout top level.
 #
 
 import sys
@@ -26,20 +26,25 @@
 import subprocess
 
 def usage():
-    print("generate_fill.py [layout_name] [-keep]")
+    print("Usage:")
+    print("generate_fill.py [<path_to_project>] [-keep] [-test]")
+    print("")
+    print("where:")
+    print("    <path_to_project> is the path to the project top level directory.")
+    print("")
+    print("  If <path_to_project> is not given, then it is assumed to be the cwd.")
+    print("  If '-keep' is specified, then keep the generation script.")
+    print("  If '-test' is specified, then create but do not run the generation script.")
     return 0
 
 if __name__ == '__main__':
 
-    if len(sys.argv) == 1:
-        usage()
-        sys.exit(0)
-
     optionlist = []
     arguments = []
 
     debugmode = False
     keepmode = False
+    testmode = False
 
     for option in sys.argv[1:]:
         if option.find('-', 0) == 0:
@@ -50,62 +55,212 @@
     if len(arguments) > 1:
         print("Wrong number of arguments given to generate_fill.py.")
         usage()
-        sys.exit(0)
+        sys.exit(1)
 
     if len(arguments) == 1:
-        project = arguments[0]
+        user_project_path = arguments[0]
     else:
-        project = 'caravel'
+        user_project_path = os.getcwd()
+
+    if not os.path.isdir(user_project_path):
+        print('Error:  Project path "' + user_project_path + '" does not exist or is not readable.')
+        sys.exit(1)
+
+    # Check for valid user ID
+    user_id_value = None
+    if os.path.isfile(user_project_path + '/info.yaml'):
+        with open(user_project_path + '/info.yaml', 'r') as ifile:
+            infolines = ifile.read().splitlines()
+            for line in infolines:
+                kvpair = line.split(':')
+                if len(kvpair) == 2:
+                    key = kvpair[0].strip()
+                    value = kvpair[1].strip()
+                    if key == 'project_id':
+                        user_id_value = value.strip('"\'')
+                        break
+
+    project = 'caravel'
+    if user_id_value:
+        project_with_id = project + '_' + user_id_value
+    else:
+        print('Error:  No project_id found in info.yaml file.')
+        sys.exit(1)
 
     if '-debug' in optionlist:
         debugmode = True
     if '-keep' in optionlist:
         keepmode = True
+    if '-test' in optionlist:
+        testmode = True
 
-    magdir = '../mag'
-    rcfile = magdir + '/.magicrc'
+    magpath = user_project_path + '/mag'
+    rcfile = magpath + '/.magicrc'
 
-    with open(magdir + '/generate_fill.tcl', 'w') as ofile:
+    if not os.path.isfile(rcfile):
+        rcfile = None
+
+    topdir = user_project_path
+    gdsdir = topdir + '/gds'
+    hasgdsdir = True if os.path.isdir(gdsdir) else False
+
+    with open(magpath + '/generate_fill.tcl', 'w') as ofile:
         print('#!/bin/env wish', file=ofile)
         print('drc off', file=ofile)
-        print('load ' + project + ' -dereference', file=ofile)
+        print('tech unlock *', file=ofile)
+        print('snap internal', file=ofile)
+        print('box values 0 0 0 0', file=ofile)
+        print('box size 700um 700um', file=ofile)
+        print('set stepbox [box values]', file=ofile)
+        print('set stepwidth [lindex $stepbox 2]', file=ofile)
+        print('set stepheight [lindex $stepbox 3]', file=ofile)
+        print('', file=ofile)
+        print('set starttime [orig_clock format [orig_clock seconds] -format "%D %T"]', file=ofile)
+        print('puts stdout "Started: $starttime"', file=ofile)
+        print('', file=ofile)
+        # Read the user project from GDS, as there is not necessarily a magic database file
+        # to go along with this.
+        # print('gds read ../gds/user_project_wrapper', file=ofile)
+        # Now read the full caravel project
+        # print('load ' + project + ' -dereference', file=ofile)
+        print('gds readonly true', file=ofile)
+        print('gds rescale false', file=ofile)
+        print('gds read ../gds/caravel', file=ofile)
         print('select top cell', file=ofile)
         print('expand', file=ofile)
+        print('cif ostyle wafflefill(tiled)', file=ofile)
+        print('', file=ofile)
+        print('set fullbox [box values]', file=ofile)
+        print('set xmax [lindex $fullbox 2]', file=ofile)
+        print('set xmin [lindex $fullbox 0]', file=ofile)
+        print('set fullwidth [expr {$xmax - $xmin}]', file=ofile)
+        print('set xtiles [expr {int(ceil(($fullwidth + 0.0) / $stepwidth))}]', file=ofile)
+        print('set ymax [lindex $fullbox 3]', file=ofile)
+        print('set ymin [lindex $fullbox 1]', file=ofile)
+        print('set fullheight [expr {$ymax - $ymin}]', file=ofile)
+        print('set ytiles [expr {int(ceil(($fullheight + 0.0) / $stepheight))}]', file=ofile)
+        print('box size $stepwidth $stepheight', file=ofile)
+        print('set xbase [lindex $fullbox 0]', file=ofile)
+        print('set ybase [lindex $fullbox 1]', file=ofile)
+        print('', file=ofile)
+
+        # Break layout into tiles and process each separately
+        print('for {set y 0} {$y < $ytiles} {incr y} {', file=ofile)
+        print('    for {set x 0} {$x < $xtiles} {incr x} {', file=ofile)
+        print('        set xlo [expr $xbase + $x * $stepwidth]', file=ofile)
+        print('        set ylo [expr $ybase + $y * $stepheight]', file=ofile)
+        print('        set xhi [expr $xlo + $stepwidth]', file=ofile)
+        print('        set yhi [expr $ylo + $stepheight]', file=ofile)
+        print('        if {$xhi > $fullwidth} {set xhi $fullwidth}', file=ofile)
+        print('        if {$yhi > $fullheight} {set yhi $fullheight}', file=ofile)
+        print('        box values $xlo $ylo $xhi $yhi', file=ofile)
+        # The flattened area must be larger than the fill tile by >1.5um
+        print('        box grow c 1.6um', file=ofile)
 
         # Flatten into a cell with a new name
-        print('puts stdout "Flattening layout. . . "', file=ofile)
-        print('flatten -nolabels ' + project + '_fill_pattern', file=ofile)
-        print('load ' + project + '_fill_pattern', file=ofile)
+        print('        puts stdout "Flattening layout of tile x=$x y=$y. . . "', file=ofile)
+        print('        flush stdout', file=ofile)
+        print('        update idletasks', file=ofile)
+        print('        flatten -dobox -nolabels ' + project_with_id + '_fill_pattern_${x}_$y', file=ofile)
+        print('        load ' + project_with_id + '_fill_pattern_${x}_$y', file=ofile)
 
-        # Remove any GDS_FILE reference
-        print('property GDS_FILE ""', file=ofile)
-        print('cif ostyle wafflefill', file=ofile)
-        print('puts stdout "Writing GDS. . . "', file=ofile)
-        print('gds write ../gds/' + project + '_fill_pattern.gds', file=ofile)
+        # Remove any GDS_FILE reference (there should not be any?)
+        print('        property GDS_FILE ""', file=ofile)
+        # Set boundary using comment layer, to the size of the step box
+	# This corresponds to the "topbox" rule in the wafflefill(tiled) style
+        print('        select top cell', file=ofile)
+        print('        erase comment', file=ofile)
+        print('        box values $xlo $ylo $xhi $yhi', file=ofile)
+        print('        paint comment', file=ofile)
+        print('        puts stdout "Writing GDS. . . "', file=ofile)
+        print('        flush stdout', file=ofile)
+        print('        update idletasks', file=ofile)
+        print('        gds write ' + project_with_id + '_fill_pattern_${x}_$y.gds', file=ofile)
+
+        # Reload project top
+        print('        load ' + project, file=ofile)
+
+        # Remove last generated cell to save memory
+        print('        cellname delete ' + project_with_id + '_fill_pattern_${x}_$y', file=ofile)
+
+        print('    }', file=ofile)
+        print('}', file=ofile)
+
+        # Now create simple "fake" views of all the tiles.
+        print('gds readonly true', file=ofile)
+        print('gds rescale false', file=ofile)
+        print('for {set y 0} {$y < $ytiles} {incr y} {', file=ofile)
+        print('    for {set x 0} {$x < $xtiles} {incr x} {', file=ofile)
+        print('        set xlo [expr $xbase + $x * $stepwidth]', file=ofile)
+        print('        set ylo [expr $ybase + $y * $stepheight]', file=ofile)
+        print('        set xhi [expr $xlo + $stepwidth]', file=ofile)
+        print('        set yhi [expr $ylo + $stepheight]', file=ofile)
+        print('        load ' + project_with_id + '_fill_pattern_${x}_$y -quiet', file=ofile)
+        print('        box values $xlo $ylo $xhi $yhi', file=ofile)
+        print('        paint comment', file=ofile)
+        print('        property FIXED_BBOX "$xlo $ylo $xhi $yhi"', file=ofile)
+        print('        property GDS_FILE ' + project_with_id + '_fill_pattern_${x}_${y}.gds', file=ofile)
+        print('        property GDS_START 0', file=ofile)
+        print('    }', file=ofile)
+        print('}', file=ofile)
+
+        # Now tile everything back together
+        print('load ' + project_with_id + '_fill_pattern -quiet', file=ofile)
+        print('for {set y 0} {$y < $ytiles} {incr y} {', file=ofile)
+        print('    for {set x 0} {$x < $xtiles} {incr x} {', file=ofile)
+        print('        box values 0 0 0 0', file=ofile)
+        print('        getcell ' + project_with_id + '_fill_pattern_${x}_$y child 0 0', file=ofile)
+        print('    }', file=ofile)
+        print('}', file=ofile)
+
+        # And write final GDS
+        print('puts stdout "Writing final GDS"', file=ofile)
+
+        print('cif *hier write disable', file=ofile)
+        print('cif *array write disable', file=ofile)
+        if hasgdsdir:
+            print('gds write ../gds/' + project_with_id + '_fill_pattern.gds', file=ofile)
+        else:
+            print('gds write ' + project_with_id + '_fill_pattern.gds', file=ofile)
+        print('set endtime [orig_clock format [orig_clock seconds] -format "%D %T"]', file=ofile)
+        print('puts stdout "Ended: $endtime"', file=ofile)
         print('quit -noprompt', file=ofile)
 
     myenv = os.environ.copy()
     myenv['MAGTYPE'] = 'mag'
 
-    mproc = subprocess.run(['magic', '-dnull', '-noconsole',
-		'-rcfile', rcfile, magdir + '/generate_fill.tcl'],
+    if not testmode:
+        # Diagnostic
+        # print('This script will generate file ' + project_with_id + '_fill_pattern.gds')
+        print('This script will generate files ' + project_with_id + '_fill_pattern_x_y.gds')
+        print('Now generating fill patterns.  This may take. . . quite. . . a while.', flush=True)
+        mproc = subprocess.run(['magic', '-dnull', '-noconsole',
+		'-rcfile', rcfile, magpath + '/generate_fill.tcl'],
 		stdin = subprocess.DEVNULL,
 		stdout = subprocess.PIPE,
 		stderr = subprocess.PIPE,
-		cwd = magdir,
+		cwd = magpath,
 		env = myenv,
 		universal_newlines = True)
-    if mproc.stdout:
-        for line in mproc.stdout.splitlines():
-            print(line)
-    if mproc.stderr:
-        print('Error message output from magic:')
-        for line in mproc.stderr.splitlines():
-            print(line)
-        if mproc.returncode != 0:
-            print('ERROR:  Magic exited with status ' + str(mproc.returncode))
+        if mproc.stdout:
+            for line in mproc.stdout.splitlines():
+                print(line)
+        if mproc.stderr:
+            print('Error message output from magic:')
+            for line in mproc.stderr.splitlines():
+                print(line)
+            if mproc.returncode != 0:
+                print('ERROR:  Magic exited with status ' + str(mproc.returncode))
 
     if not keepmode:
-        os.remove(magdir + '/generate_fill.tcl')
+        # Remove fill generation script
+        os.remove(magpath + '/generate_fill.tcl')
+        # Remove all individual fill tiles, leaving only the composite GDS.
+        filelist = os.listdir(magpath)
+        for file in filelist:
+            if os.path.splitext(magpath + '/' + file)[1] == '.gds':
+                if file.startswith(project + '_fill_pattern_'):
+                    os.remove(magpath + '/' + file)
 
+    print('Done!')
     exit(0)