diff --git a/sky130/custom/scripts/check_density.py b/sky130/custom/scripts/check_density.py
index 9b759a6..feccc60 100755
--- a/sky130/custom/scripts/check_density.py
+++ b/sky130/custom/scripts/check_density.py
@@ -544,7 +544,7 @@
     liaccum = sum(lifill) / atotal
     print('')
     print('LI Density: ' + str(liaccum))
-    if liaccum < 0.50:
+    if liaccum < 0.35:
         print('***Error:  LI Density < 35%')
     elif liaccum > 0.60:
         print('***Error:  LI Density > 60%')
diff --git a/sky130/custom/scripts/generate_fill.py b/sky130/custom/scripts/generate_fill.py
index 1f9254f..74b0c36 100755
--- a/sky130/custom/scripts/generate_fill.py
+++ b/sky130/custom/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");
@@ -23,19 +23,53 @@
 import sys
 import os
 import re
+import glob
 import subprocess
+import multiprocessing
 
 def usage():
     print("Usage:")
-    print("generate_fill.py <layout_name> [-keep] [-test]")
+    print("generate_fill.py <layout_name> [-keep] [-test] [-dist]")
     print("")
     print("where:")
     print("    <layout_name> is the path to the .mag file to be filled.")
     print("")
     print("  If '-keep' is specified, then keep the generation script.")
     print("  If '-test' is specified, then create but do not run the generation script.")
+    print("  If '-dist' is specified, then run distributed (multi-processing).")
     return 0
 
+def makegds(file):
+    # Procedure for multiprocessing only:  Run the distributed processing
+    # script to load a .mag file of one flattened square area of the layout,
+    # and run the fill generator to produce a .gds file output from it.
+
+    magpath = os.path.split(file)[0]
+    filename = os.path.split(file)[1]
+
+    myenv = os.environ.copy()
+    myenv['MAGTYPE'] = 'mag'
+
+    mproc = subprocess.run(['magic', '-dnull', '-noconsole',
+		'-rcfile', rcfile, magpath + '/generate_fill_dist.tcl',
+		filename],
+		stdin = subprocess.DEVNULL,
+		stdout = subprocess.PIPE,
+		stderr = subprocess.PIPE,
+		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 __name__ == '__main__':
 
     optionlist = []
@@ -44,6 +78,7 @@
     debugmode = False
     keepmode = False
     testmode = False
+    distmode = False
 
     for option in sys.argv[1:]:
         if option.find('-', 0) == 0:
@@ -79,6 +114,8 @@
         keepmode = True
     if '-test' in optionlist:
         testmode = True
+    if '-dist' in optionlist:
+        distmode = True
 
     rcfile = magpath + '/.magicrc'
     if not os.path.isfile(rcfile):
@@ -90,120 +127,171 @@
     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)
+    ofile = open(magpath + '/generate_fill.tcl', 'w') 
+
+    print('#!/usr/bin/env wish', file=ofile)
+    print('drc off', 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)
+    print('load ' + project + ' -dereference', file=ofile)
+    print('select top cell', file=ofile)
+    print('expand', file=ofile)
+    if not distmode:
+        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 $yhi', file=ofile)
+    # The flattened area must be larger than the fill tile by >1.5um
+    print('        box grow c 1.6um', file=ofile)
+
+    # Flatten into a cell with a new name
+    print('        puts stdout "Flattening layout of tile x=$x y=$y. . . "', file=ofile)
+    print('        flush stdout', file=ofile)
+    print('        update idletasks', file=ofile)
+    print('        flatten -dobox -nolabels ' + project + '_fill_pattern_${x}_$y', file=ofile)
+    print('        load ' + project + '_fill_pattern_${x}_$y', 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 $yhi', file=ofile)
+    print('        paint comment', file=ofile)
+
+    if not distmode:
+        print('        puts stdout "Writing GDS. . . "', file=ofile)
+
+    print('        flush stdout', file=ofile)
+    print('        update idletasks', file=ofile)
+
+    if distmode:
+        print('        writeall force ' + project + '_fill_pattern_${x}_$y', file=ofile)
+    else:
+        print('        gds write ' + project + '_fill_pattern_${x}_$y.gds', file=ofile)
+
+    # Reload project top
+    print('        load ' + project, file=ofile)
+
+    # Remove last generated cell to save memory
+    print('        cellname delete ' + project + '_fill_pattern_${x}_$y', file=ofile)
+
+    print('    }', file=ofile)
+    print('}', file=ofile)
+
+    if distmode:
+        print('set ofile [open fill_gen_info.txt w]', file=ofile)
+        print('puts $ofile "$stepwidth"', file=ofile)
+        print('puts $ofile "$stepheight"', file=ofile)
+        print('puts $ofile "$xtiles"', file=ofile)
+        print('puts $ofile "$ytiles"', file=ofile)
+        print('puts $ofile "$xbase"', file=ofile)
+        print('puts $ofile "$ybase"', file=ofile)
+        print('close $ofile', file=ofile)
+        print('quit -noprompt', file=ofile)
+        ofile.close()
+
+        with open(magpath + '/generate_fill_dist.tcl', 'w') as ofile:
+            print('#!/usr/bin/env wish', file=ofile)
+            print('drc off', file=ofile)
+            print('tech unlock *', file=ofile)
+            print('snap internal', file=ofile)
+            print('box values 0 0 0 0', file=ofile)
+            print('set filename [file root [lindex $argv $argc-1]]', file=ofile)
+            print('load $filename', file=ofile)
+            print('cif ostyle wafflefill(tiled)', file=ofile)
+            print('gds write [file root $filename].gds', file=ofile)
+            print('quit -noprompt', file=ofile)
+
+        ofile = open(magpath + '/generate_fill_final.tcl', 'w')
+        print('#!/usr/bin/env wish', file=ofile)
         print('drc off', 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)
-        print('load ' + project + ' -dereference', 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)
+        print('set ifile [open fill_gen_info.txt r]', file=ofile)
+        print('gets $ifile stepwidth', file=ofile)
+        print('gets $ifile stepheight', file=ofile)
+        print('gets $ifile xtiles', file=ofile)
+        print('gets $ifile ytiles', file=ofile)
+        print('gets $ifile xbase', file=ofile)
+        print('gets $ifile ybase', file=ofile)
+        print('close $ifile', file=ofile)
 
-        # Flatten into a cell with a new name
-        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 + '_fill_pattern_${x}_$y', file=ofile)
-        print('        load ' + project + '_fill_pattern_${x}_$y', 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 + $stepheight]', file=ofile)
+    print('        load ' + project + '_fill_pattern_${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 $yhi"', file=ofile)
+    print('        property GDS_FILE ' + project + '_fill_pattern_${x}_${y}.gds', file=ofile)
+    print('        property GDS_START 0', file=ofile)
+    print('    }', file=ofile)
+    print('}', 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 $yhi', file=ofile)
-        print('        paint comment', file=ofile)
-        print('        puts stdout "Writing GDS. . . "', file=ofile)
-        print('        flush stdout', file=ofile)
-        print('        update idletasks', file=ofile)
-        print('        gds write ' + project + '_fill_pattern_${x}_$y.gds', file=ofile)
+    # Now tile everything back together
+    print('load ' + project + '_fill_pattern -quiet', file=ofile)
+    print('for {set y 0} {$y < $ytiles} {incr y} {', file=ofile)
+    print('    for {set x 0} {$x < $xtiles} {incr x} {', file=ofile)
+    print('        box values 0 0 0 0', file=ofile)
+    print('        getcell ' + project + '_fill_pattern_${x}_$y child 0 0', file=ofile)
+    print('    }', file=ofile)
+    print('}', file=ofile)
 
-        # Reload project top
-        print('        load ' + project, file=ofile)
+    # And write final GDS
+    print('puts stdout "Writing final GDS"', file=ofile)
 
-        # Remove last generated cell to save memory
-        print('        cellname delete ' + project + '_fill_pattern_${x}_$y', file=ofile)
+    print('cif *hier write disable', file=ofile)
+    print('cif *array write disable', file=ofile)
+    if hasgdsdir:
+        print('gds write ../gds/' + project + '_fill_pattern.gds', file=ofile)
+    else:
+        print('gds write ' + project + '_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)
+    ofile.close()
 
-        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 + $stepheight]', file=ofile)
-        print('        load ' + project + '_fill_pattern_${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 $yhi"', file=ofile)
-        print('        property GDS_FILE ' + project + '_fill_pattern_${x}_${y}.gds', file=ofile)
-        print('        property GDS_START 0', file=ofile)
-        print('    }', file=ofile)
-        print('}', file=ofile)
-
-        # Now tile everything back together
-        print('load ' + project + '_fill_pattern -quiet', file=ofile)
-        print('for {set y 0} {$y < $ytiles} {incr y} {', file=ofile)
-        print('    for {set x 0} {$x < $xtiles} {incr x} {', file=ofile)
-        print('        box values 0 0 0 0', file=ofile)
-        print('        getcell ' + project + '_fill_pattern_${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 + '_fill_pattern.gds', file=ofile)
-        else:
-            print('gds write ' + project + '_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'
 
@@ -230,6 +318,40 @@
             if mproc.returncode != 0:
                 print('ERROR:  Magic exited with status ' + str(mproc.returncode))
 
+        if distmode:
+            # If using distributed mode, then run magic on each of the generated
+            # layout files
+            pool = multiprocessing.Pool()
+            magfiles = glob.glob(magpath + '/' + project + '_fill_pattern_*.mag')
+            # NOTE:  Adding 'x' to the end of each filename, or else magic will
+            # try to read it from the command line as well as passing it as an
+            # argument to the script.  We only want it passed as an argument.
+            magxfiles = list(item + 'x' for item in magfiles)
+            pool.map(makegds, magxfiles)
+
+            # If using distributed mode, then remove all of the temporary .mag files
+            # and then run the final generation script.
+            for file in magfiles:
+                os.remove(file)
+
+            mproc = subprocess.run(['magic', '-dnull', '-noconsole',
+			'-rcfile', rcfile, magpath + '/generate_fill_final.tcl'],
+			stdin = subprocess.DEVNULL,
+			stdout = subprocess.PIPE,
+			stderr = subprocess.PIPE,
+			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 not keepmode:
         # Remove fill generation script
         os.remove(magpath + '/generate_fill.tcl')
@@ -240,5 +362,14 @@
                 if file.startswith(project + '_fill_pattern_'):
                     os.remove(magpath + '/' + file)
 
+        if distmode:
+            os.remove(magpath + '/generate_fill_dist.tcl')
+            os.remove(magpath + '/generate_fill_final.tcl')
+            os.remove(magpath + '/fill_gen_info.txt')
+            if testmode:
+                magfiles = glob.glob(magpath + '/' + project + '_fill_pattern_*.mag')
+                for file in magfiles:
+                    os.remove(file)
+
     print('Done!')
     exit(0)