diff --git a/VERSION b/VERSION
index 0b869e6..a9d3998 100644
--- a/VERSION
+++ b/VERSION
@@ -1 +1 @@
-1.0.512
+1.0.513
diff --git a/sky130/custom/scripts/check_antenna.py b/sky130/custom/scripts/check_antenna.py
index e7eb89f..cc2eb56 100755
--- a/sky130/custom/scripts/check_antenna.py
+++ b/sky130/custom/scripts/check_antenna.py
@@ -66,6 +66,9 @@
         elif 'PDK_PATH' in myenv:
             rcpathroot = myenv['PDKPATH'] + '/libs.tech/magic'
             rcfile = glob.glob(rcpathroot + '/*.magicrc')[0]
+        elif 'PDK_ROOT' in myenv and 'PDK' in myenv:
+            rcpathroot = myenv['PDK_ROOT'] + '/' + myenv['PDK'] + '/libs.tech/magic'
+            rcfile = glob.glob(rcpathroot + '/*.magicrc')[0]
         else:
             print('Error: Cannot get magic rcfile for the technology!')
             return
diff --git a/sky130/custom/scripts/check_density.py b/sky130/custom/scripts/check_density.py
index 3affd97..72bf2f9 100755
--- a/sky130/custom/scripts/check_density.py
+++ b/sky130/custom/scripts/check_density.py
@@ -23,20 +23,21 @@
 import sys
 import os
 import re
+import glob
 import select
 import subprocess
 
 def usage():
     print("Usage:")
-    print("check_density.py [<gds_file_name>] [-keep]")
+    print("check_density.py [<layout_file_name>] [-keep]")
     print("")
     print("where:")
-    print("   <gds_file_name> is the path to the .gds file to be checked.")
+    print("   <layout_file_name> is the path to the .gds or .mag file to be checked.")
     print("")
     print("  If '-keep' is specified, then keep the check script.")
+    print("  If '-debug' is specified, then print diagnostic information.")
     return 0
 
-
 if __name__ == '__main__':
 
     optionlist = []
@@ -56,60 +57,97 @@
         usage()
         sys.exit(0)
         
-    relative_path=arguments[0]
-
-    gdspath = os.getcwd()+'/'+os.path.split(relative_path)[0]+'/'
-    if gdspath == '':
-        gdspath = os.getcwd()
-
-    gds_filepath = os.path.split(relative_path)[1]
-    
-    if os.path.splitext(gds_filepath)[1] != '.gds':
-        if os.path.splitext(gds_filepath)[1] == '':
-            gds_filepath += '.gds'
-        else:
-            print('Error:  Project is not a GDS file!')
-            sys.exit(1)
-    
-    gdsname = os.path.split(gds_filepath)[1]
-    gdsroot = os.path.splitext(gdsname)[0]
-
-    # Check for valid path to the GDS file
-
-    if not os.path.isdir(gdspath):
-        print('Error:  Project path "' + gds_filepath + '" does not exist or is not readable.')
-        sys.exit(1)
-        
-    if not os.path.isfile(gdspath+gds_filepath):
-        print('Error:  Project "' + gdspath+gds_filepath + '" does not exist or is not readable.')
-        sys.exit(1)
+    # Process options
 
     if '-debug' in optionlist:
         debugmode = True
+        print('Running in debug mode.')
     if '-keep' in optionlist:
         keepmode = True
+        if debugmode:
+            print('Keeping all files after running.')
+    elif debugmode:
+        print('Temporary files will be removed after running.')
 
-    # NOTE:  There should be some attempt to find the installed PDK magicrc file
-    # if there is no mag/ directory.
-    
-    
-    # Searching for rcfile
-    
-    rcfile_paths=[gdspath+'/.magicrc','/$PDK_PATH/libs.tech/magic/TECHNAME.magicrc','/usr/share/pdk/TECHNAME/libs.tech/magic/TECHNAME.magicrc']
-    
-    rcfile=''
-    
-    for rc_path in rcfile_paths:
-        if os.path.isfile(rc_path):
-            rcfile=rc_path
-            break
-    
-    if rcfile=='':
-        print('Error: .magicrc file not found.')
+    # Find layout from command-line argument
+
+    user_project_path = arguments[0]
+
+    if os.path.split(user_project_path)[0] == '':
+        layoutpath = os.getcwd()
+    else:
+        layoutpath = os.getcwd() + '/' + os.path.split(user_project_path)[0]
+
+    # Use split() not os.path.splitext() to capture double-dot extensions
+    # like "layout.gds.gz".
+
+    project = user_project_path.split(os.extsep, 1)
+
+    if len(project) == 1:
+        # No file extension given;  figure it out
+        layoutfiles = glob.glob(layoutpath + '/' + user_project_path + '.*')
+        if len(layoutfiles) == 1:
+            proj_extension = '.' + layoutfiles[0].split(os.extsep, 1)[1]
+            user_project_path = layoutfiles[0]
+        elif len(layoutfiles) == 0:
+            if debugmode:
+                print('No matching files found for ' + layoutpath + '/' + user_project_path + '.*')
+            print('Error:  Project is not a magic database or GDS file!')
+            sys.exit(1)
+        else:
+            print('Error:  Project name is ambiguous!')
+            sys.exit(1)
+    else:
+        proj_extension = '.' + project[1]
+
+    is_mag = False
+    is_gds = False
+
+    if proj_extension == '.mag' or proj_extension == '.mag.gz':
+        is_mag = True
+    elif proj_extension == '.gds' or proj_extension == '.gds.gz':
+        is_gds = True
+    else:
+        if debugmode:
+            print('Unknown extension ' + proj_extension + ' in filename.')
+        print('Error:  Project is not a magic database or GDS file!')
         sys.exit(1)
 
+    if not os.path.isfile(user_project_path):
+        print('Error:  Project "' + user_project_path + '" does not exist or is not readable.')
+        sys.exit(1)
+
+    # The path where the fill generation script resides should be the same
+    # path where the magic startup script resides, for the same PDK
+    scriptpath = os.path.dirname(os.path.realpath(__file__))
     
-    with open(gdspath + '/check_density.tcl', 'w') as ofile:
+    # Search for a magic startup script.  Order of precedence:
+    #  1. PDK_ROOT environment variable
+    #  2. Local .magicrc
+    #  3. The location of this script
+
+    if os.environ.get('PDK'):
+        pdk_name = os.environ.get('PDK')
+    else:
+        pdk_name = 'sky130A'
+
+    if os.environ.get('PDK_ROOT'):
+        rcfile_path = os.environ.get('PDK_ROOT') + '/' + pdk_name + '/libs.tech/magic/' + pdk_name + '.magicrc'
+    elif os.path.isfile(layoutpath + '/.magicrc'):
+        rcfile_path = layoutpath + '/.magicrc'
+    elif os.path.isfile(scriptpath + '/' + pdk_name + '.magicrc'):
+        rcfile_path = scriptpath + '/' + pdk_name + '.magicrc'
+    else:
+        print('Unknown path to magic startup script.  Please set $PDK_ROOT')
+        sys.exit(1)
+
+    project_file = os.path.split(user_project_path)[1]
+    project = project_file.split(os.extsep, 1)[0]
+    
+    # Create the Tcl script to run in magic to check local density across
+    # stepped regions.
+
+    with open(layoutpath + '/check_density.tcl', 'w') as ofile:
         print('#!/bin/env wish', file=ofile)
         print('crashbackups stop', file=ofile)
         print('drc off', file=ofile)
@@ -121,15 +159,16 @@
         print('flush stdout', file=ofile)
         print('update idletasks', file=ofile)
 
-        # Read GDS file
-        print('gds readonly true', file=ofile)
-        print('gds rescale false', file=ofile)
-        print('gds read ' + gds_filepath, file=ofile)
-        print('', file=ofile)
+        if is_gds:
+            # Read GDS file
+            print('gds readonly true', file=ofile)
+            print('gds rescale false', file=ofile)
+            print('gds read ' + project_file, file=ofile)
+            print('', file=ofile)
 
         # NOTE:  This assumes that the name of the GDS file is the name of the
         # topmost cell (which should be passed as an option)
-        print('load ' + gdsroot, file=ofile)
+        print('load ' + project, file=ofile)
         print('', file=ofile)
 
         print('set midtime [orig_clock format [orig_clock seconds] -format "%D %T"]', file=ofile)
@@ -153,6 +192,8 @@
         print('select top cell', file=ofile)
         print('expand', file=ofile)
         print('set fullbox [box values]', file=ofile)
+        # Override with FIXED_BBOX, if it is defined
+        print('catch {set fullbox [property FIXED_BBOX]}', 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)
@@ -171,10 +212,10 @@
         print('', file=ofile)
 
         # Need to know what fraction of a full tile is the last row and column
-        print('set xfrac [expr {($xtiles * $stepsizex - $fullwidth + 0.0) / $stepsizex}]', file=ofile)
-        print('set yfrac [expr {($ytiles * $stepsizey - $fullheight + 0.0) / $stepsizey}]', file=ofile)
+        print('set xfrac [expr {1.0 - ($xtiles * $stepsizex - $fullwidth + 0.0) / $stepsizex}]', file=ofile)
+        print('set yfrac [expr {1.0 - ($ytiles * $stepsizey - $fullheight + 0.0) / $stepsizey}]', file=ofile)
 
-        # If the last row/column fraction is zero, then set to 1
+        # If the last row/column fraction is zero, then set to 1 (might never happen?)
         print('if {$xfrac == 0.0} {set xfrac 1.0}', file=ofile)
         print('if {$yfrac == 0.0} {set yfrac 1.0}', file=ofile)
 
@@ -221,7 +262,7 @@
         print('        flush stdout', file=ofile)
         print('        update idletasks', file=ofile)
 
-        print('        load ' + gdsroot, file=ofile)
+        print('        load ' + project, file=ofile)
         print('        cellname delete tile', file=ofile)
 
         print('    }', file=ofile)
@@ -236,14 +277,20 @@
     myenv = os.environ.copy()
     myenv['MAGTYPE'] = 'mag'
 
-    print('Running density checks on file ' + gds_filepath, flush=True)
+    print('Running density checks on file ' + user_project_path, flush=True)
     
-    mproc = subprocess.Popen(['magic', '-dnull', '-noconsole',
-		'-rcfile', rcfile, gdspath + '/check_density.tcl'],
+    magic_run_opts = [
+		'magic',
+		'-dnull',
+		'-noconsole',
+		'-rcfile', rcfile_path,
+		layoutpath + '/check_density.tcl']
+
+    mproc = subprocess.Popen(magic_run_opts,
 		stdin = subprocess.DEVNULL,
 		stdout = subprocess.PIPE,
 		stderr = subprocess.PIPE,
-		cwd = gdspath,
+		cwd = layoutpath,
 		env = myenv,
 		universal_newlines = True)
 
@@ -307,6 +354,8 @@
 
     for line in dlines:
         dpair = line.split(':')
+        if debugmode:
+            print('Magic output line: ' + line)
         if len(dpair) == 2:
             layer = dpair[0]
             try:
@@ -349,40 +398,52 @@
     total_tiles = (ytiles - 9) * (xtiles - 9)
 
     print('')
-    print('Density results (total tiles = ' + str(total_tiles) + '):')
+    print('Stepped area density results (total tiles = ' + str(total_tiles) + '):')
 
     # Full areas are 10 x 10 tiles = 100.  But the right and top sides are
     # not full tiles, so the full area must be prorated.
 
-    sideadjust = 90.0 + (10.0 * xfrac)
-    topadjust = 90.0 + (10.0 * yfrac)
+    print('Side adjustment = ' + '{:.3f}'.format(xfrac))
+    print('Top adjustment = ' + '{:.3f}'.format(yfrac))
 
-    corneradjust = 81.0 + (9.0 * xfrac) + (9.0 * yfrac) + (xfrac * yfrac)
-
-    print('Side adjustment = ' + str(sideadjust))
-    print('Top adjustment = ' + str(topadjust))
-    print('Corner adjustment = ' + str(corneradjust))
+    if debugmode:
+        with open('tile_densities.txt', 'w') as dfile:
+            print(str(fomfill), file=dfile)
+            print(str(polyfill), file=dfile)
+            print(str(lifill), file=dfile)
+            print(str(met1fill), file=dfile)
+            print(str(met2fill), file=dfile)
+            print(str(met3fill), file=dfile)
+            print(str(met4fill), file=dfile)
+            print(str(met5fill), file=dfile)
 
     print('')
     print('FOM Density:')
     for y in range(0, ytiles - 9):
         if y == ytiles - 10:
-            atotal = topadjust
+            locyfrac = yfrac
         else:
-            atotal = 100.0
+            locyfrac = 1.0
         for x in range(0, xtiles - 9):
             if x == xtiles - 10:
-                if y == ytiles - 10:
-                    atotal = corneradjust
-                else:
-                    atotal = sideadjust
+                locxfrac = xfrac
+            else:
+                locxfrac = 1.0
+
             fomaccum = 0
-            for w in range(y, y + 10):
+            atotal = 81.0 + 9.0 * locxfrac + 9.0 * locyfrac + locxfrac * locyfrac
+
+            for w in range(y, y + 9):
                 base = xtiles * w + x
-                fomaccum += sum(fomfill[base : base + 10])
+                fomaccum += sum(fomfill[base : base + 9])
+                fomaccum += fomfill[base + 9] * locxfrac
+            base = xtiles * (y + 9) + x
+            fomaccum += sum(fomfill[base : base + 9]) * locyfrac
+            fomaccum += fomfill[base + 9] * locxfrac * locyfrac
                     
             fomaccum /= atotal
-            print('Tile (' + str(x) + ', ' + str(y) + '):   ' + str(fomaccum))
+            fomstr = "{:.3f}".format(fomaccum)
+            print('Tile (' + str(x) + ', ' + str(y) + '):   ' + fomstr)
             if fomaccum < 0.33:
                 print('***Error:  FOM Density < 33%')
             elif fomaccum > 0.57:
@@ -392,43 +453,57 @@
     print('POLY Density:')
     for y in range(0, ytiles - 9):
         if y == ytiles - 10:
-            atotal = topadjust
+            locyfrac = yfrac
         else:
-            atotal = 100.0
+            locyfrac = 1.0
         for x in range(0, xtiles - 9):
             if x == xtiles - 10:
-                if y == ytiles - 10:
-                    atotal = corneradjust
-                else:
-                    atotal = sideadjust
+                locxfrac = xfrac
+            else:
+                locxfrac = 1.0
+
             polyaccum = 0
-            for w in range(y, y + 10):
+            atotal = 81.0 + 9.0 * locxfrac + 9.0 * locyfrac + locxfrac * locyfrac
+
+            for w in range(y, y + 9):
                 base = xtiles * w + x
-                polyaccum += sum(polyfill[base : base + 10])
+                polyaccum += sum(polyfill[base : base + 9])
+                polyaccum += polyfill[base + 9] * locxfrac
+            base = xtiles * (y + 9) + x
+            polyaccum += sum(polyfill[base : base + 9]) * locyfrac
+            polyaccum += polyfill[base + 9] * locxfrac * locyfrac
                     
             polyaccum /= atotal
-            print('Tile (' + str(x) + ', ' + str(y) + '):   ' + str(polyaccum))
+            polystr = "{:.3f}".format(polyaccum)
+            print('Tile (' + str(x) + ', ' + str(y) + '):   ' + polystr)
 
     print('')
     print('LI Density:')
     for y in range(0, ytiles - 9):
         if y == ytiles - 10:
-            atotal = topadjust
+            locyfrac = yfrac
         else:
-            atotal = 100.0
+            locyfrac = 1.0
         for x in range(0, xtiles - 9):
             if x == xtiles - 10:
-                if y == ytiles - 10:
-                    atotal = corneradjust
-                else:
-                    atotal = sideadjust
+                locxfrac = xfrac
+            else:
+                locxfrac = 1.0
+
             liaccum = 0
-            for w in range(y, y + 10):
+            atotal = 81.0 + 9.0 * locxfrac + 9.0 * locyfrac + locxfrac * locyfrac
+
+            for w in range(y, y + 9):
                 base = xtiles * w + x
-                liaccum += sum(lifill[base : base + 10])
+                liaccum += sum(lifill[base : base + 9])
+                liaccum += lifill[base + 9] * locxfrac
+            base = xtiles * (y + 9) + x
+            liaccum += sum(lifill[base : base + 9]) * locyfrac
+            liaccum += lifill[base + 9] * locxfrac * locyfrac
                     
             liaccum /= atotal
-            print('Tile (' + str(x) + ', ' + str(y) + '):   ' + str(liaccum))
+            listr = "{:.3f}".format(liaccum)
+            print('Tile (' + str(x) + ', ' + str(y) + '):   ' + listr)
             if liaccum < 0.35:
                 print('***Error:  LI Density < 35%')
             elif liaccum > 0.60:
@@ -438,22 +513,29 @@
     print('MET1 Density:')
     for y in range(0, ytiles - 9):
         if y == ytiles - 10:
-            atotal = topadjust
+            locyfrac = yfrac
         else:
-            atotal = 100.0
+            locyfrac = 1.0
         for x in range(0, xtiles - 9):
             if x == xtiles - 10:
-                if y == ytiles - 10:
-                    atotal = corneradjust
-                else:
-                    atotal = sideadjust
+                locxfrac = xfrac
+            else:
+                locxfrac = 1.0
+
             met1accum = 0
-            for w in range(y, y + 10):
+            atotal = 81.0 + 9.0 * locxfrac + 9.0 * locyfrac + locxfrac * locyfrac
+
+            for w in range(y, y + 9):
                 base = xtiles * w + x
-                met1accum += sum(met1fill[base : base + 10])
+                met1accum += sum(met1fill[base : base + 9])
+                met1accum += met1fill[base + 9] * locxfrac
+            base = xtiles * (y + 9) + x
+            met1accum += sum(met1fill[base : base + 9]) * locyfrac
+            met1accum += met1fill[base + 9] * locxfrac * locyfrac
                     
             met1accum /= atotal
-            print('Tile (' + str(x) + ', ' + str(y) + '):   ' + str(met1accum))
+            met1str = "{:.3f}".format(met1accum)
+            print('Tile (' + str(x) + ', ' + str(y) + '):   ' + met1str)
             if met1accum < 0.35:
                 print('***Error:  MET1 Density < 35%')
             elif met1accum > 0.60:
@@ -463,22 +545,29 @@
     print('MET2 Density:')
     for y in range(0, ytiles - 9):
         if y == ytiles - 10:
-            atotal = topadjust
+            locyfrac = yfrac
         else:
-            atotal = 100.0
+            locyfrac = 1.0
         for x in range(0, xtiles - 9):
             if x == xtiles - 10:
-                if y == ytiles - 10:
-                    atotal = corneradjust
-                else:
-                    atotal = sideadjust
+                locxfrac = xfrac
+            else:
+                locxfrac = 1.0
+
             met2accum = 0
-            for w in range(y, y + 10):
+            atotal = 81.0 + 9.0 * locxfrac + 9.0 * locyfrac + locxfrac * locyfrac
+
+            for w in range(y, y + 9):
                 base = xtiles * w + x
-                met2accum += sum(met2fill[base : base + 10])
+                met2accum += sum(met2fill[base : base + 9])
+                met2accum += met2fill[base + 9] * locxfrac
+            base = xtiles * (y + 9) + x
+            met2accum += sum(met2fill[base : base + 9]) * locyfrac
+            met2accum += met2fill[base + 9] * locxfrac * locyfrac
                     
             met2accum /= atotal
-            print('Tile (' + str(x) + ', ' + str(y) + '):   ' + str(met2accum))
+            met2str = "{:.3f}".format(met2accum)
+            print('Tile (' + str(x) + ', ' + str(y) + '):   ' + met2str)
             if met2accum < 0.35:
                 print('***Error:  MET2 Density < 35%')
             elif met2accum > 0.60:
@@ -488,22 +577,29 @@
     print('MET3 Density:')
     for y in range(0, ytiles - 9):
         if y == ytiles - 10:
-            atotal = topadjust
+            locyfrac = yfrac
         else:
-            atotal = 100.0
+            locyfrac = 1.0
         for x in range(0, xtiles - 9):
             if x == xtiles - 10:
-                if y == ytiles - 10:
-                    atotal = corneradjust
-                else:
-                    atotal = sideadjust
+                locxfrac = xfrac
+            else:
+                locxfrac = 1.0
+
             met3accum = 0
-            for w in range(y, y + 10):
+            atotal = 81.0 + 9.0 * locxfrac + 9.0 * locyfrac + locxfrac * locyfrac
+
+            for w in range(y, y + 9):
                 base = xtiles * w + x
-                met3accum += sum(met3fill[base : base + 10])
+                met3accum += sum(met3fill[base : base + 9])
+                met3accum += met3fill[base + 9] * locxfrac
+            base = xtiles * (y + 9) + x
+            met3accum += sum(met3fill[base : base + 9]) * locyfrac
+            met3accum += met3fill[base + 9] * locxfrac * locyfrac
                     
             met3accum /= atotal
-            print('Tile (' + str(x) + ', ' + str(y) + '):   ' + str(met3accum))
+            met3str = "{:.3f}".format(met3accum)
+            print('Tile (' + str(x) + ', ' + str(y) + '):   ' + met3str)
             if met3accum < 0.35:
                 print('***Error:  MET3 Density < 35%')
             elif met3accum > 0.60:
@@ -513,22 +609,30 @@
     print('MET4 Density:')
     for y in range(0, ytiles - 9):
         if y == ytiles - 10:
-            atotal = topadjust
+            locyfrac = yfrac
         else:
-            atotal = 100.0
+            locyfrac = 1.0
+
         for x in range(0, xtiles - 9):
             if x == xtiles - 10:
-                if y == ytiles - 10:
-                    atotal = corneradjust
-                else:
-                    atotal = sideadjust
+                locxfrac = xfrac
+            else:
+                locxfrac = 1.0
+
             met4accum = 0
-            for w in range(y, y + 10):
+            atotal = 81.0 + 9.0 * locxfrac + 9.0 * locyfrac + locxfrac * locyfrac
+
+            for w in range(y, y + 9):
                 base = xtiles * w + x
-                met4accum += sum(met4fill[base : base + 10])
+                met4accum += sum(met4fill[base : base + 9])
+                met4accum += met4fill[base + 9] * locxfrac
+            base = xtiles * (y + 9) + x
+            met4accum += sum(met4fill[base : base + 9]) * locyfrac
+            met4accum += met4fill[base + 9] * locxfrac * locyfrac
                     
             met4accum /= atotal
-            print('Tile (' + str(x) + ', ' + str(y) + '):   ' + str(met4accum))
+            met4str = "{:.3f}".format(met4accum)
+            print('Tile (' + str(x) + ', ' + str(y) + '):   ' + met4str)
             if met4accum < 0.35:
                 print('***Error:  MET4 Density < 35%')
             elif met4accum > 0.60:
@@ -538,95 +642,182 @@
     print('MET5 Density:')
     for y in range(0, ytiles - 9):
         if y == ytiles - 10:
-            atotal = topadjust
+            locyfrac = yfrac
         else:
-            atotal = 100.0
+            locyfrac = 1.0
         for x in range(0, xtiles - 9):
             if x == xtiles - 10:
-                if y == ytiles - 10:
-                    atotal = corneradjust
-                else:
-                    atotal = sideadjust
+                locxfrac = xfrac
+            else:
+                locxfrac = 1.0
+
             met5accum = 0
-            for w in range(y, y + 10):
+            atotal = 81.0 + 9.0 * locxfrac + 9.0 * locyfrac + locxfrac * locyfrac
+
+            for w in range(y, y + 9):
                 base = xtiles * w + x
-                met5accum += sum(met5fill[base : base + 10])
+                met5accum += sum(met5fill[base : base + 9])
+                met5accum += met5fill[base + 9] * locxfrac
+            base = xtiles * (y + 9) + x
+            met5accum += sum(met5fill[base : base + 9]) * locyfrac
+            met5accum += met5fill[base + 9] * locxfrac * locyfrac
                     
             met5accum /= atotal
-            print('Tile (' + str(x) + ', ' + str(y) + '):   ' + str(met5accum))
+            met5str = "{:.3f}".format(met5accum)
+            print('Tile (' + str(x) + ', ' + str(y) + '):   ' + met5str)
             if met5accum < 0.45:
                 print('***Error:  MET5 Density < 45%')
             elif met5accum > 0.76:
                 print('***Error:  MET5 Density > 76%')
 
     print('')
-    print('Whole-chip density results:')
+    print('Whole-chip (global) density results:')
 
     atotal = ((xtiles - 1.0) * (ytiles - 1.0)) + ((ytiles - 1.0) * xfrac) + ((xtiles - 1.0) * yfrac) + (xfrac * yfrac)
 
-    fomaccum = sum(fomfill) / atotal
+    fomaccum = 0
+    for y in range(0, ytiles - 1):
+        base = xtiles * y
+        fomaccum += sum(fomfill[base:base + xtiles - 1])
+        fomaccum += fomfill[base + xtiles - 1] * xfrac
+    base = xtiles * (ytiles - 1)
+    fomaccum += sum(fomfill[base:base + xtiles - 1]) * yfrac
+    fomaccum += fomfill[base + xtiles - 1] * xfrac * yfrac
+
+    fomaccum /= atotal
+    fomstr = "{:.3f}".format(fomaccum)
     print('')
-    print('FOM Density: ' + str(fomaccum))
+    print('FOM Density: ' + fomstr)
     if fomaccum < 0.33:
         print('***Error:  FOM Density < 33%')
     elif fomaccum > 0.57:
         print('***Error:  FOM Density > 57%')
 
-    polyaccum = sum(polyfill) / atotal
-    print('')
-    print('POLY Density: ' + str(polyaccum))
+    polyaccum = 0
+    for y in range(0, ytiles - 1):
+        base = xtiles * y
+        polyaccum += sum(polyfill[base:base + xtiles - 1])
+        polyaccum += polyfill[base + xtiles - 1] * xfrac
+    base = xtiles * (ytiles - 1)
+    polyaccum += sum(polyfill[base:base + xtiles - 1]) * yfrac
+    polyaccum += polyfill[base + xtiles - 1] * xfrac * yfrac
 
-    liaccum = sum(lifill) / atotal
+    polyaccum /= atotal
+    polystr = "{:.3f}".format(polyaccum)
     print('')
-    print('LI Density: ' + str(liaccum))
+    print('POLY Density: ' + polystr)
+
+    liaccum = 0
+    for y in range(0, ytiles - 1):
+        base = xtiles * y
+        liaccum += sum(lifill[base:base + xtiles - 1])
+        liaccum += lifill[base + xtiles - 1] * xfrac
+    base = xtiles * (ytiles - 1)
+    liaccum += sum(lifill[base:base + xtiles - 1]) * yfrac
+    liaccum += lifill[base + xtiles - 1] * xfrac * yfrac
+
+    liaccum /= atotal
+    listr = "{:.3f}".format(liaccum)
+    print('')
+    print('LI Density: ' + listr)
     if liaccum < 0.35:
         print('***Error:  LI Density < 35%')
     elif liaccum > 0.60:
         print('***Error:  LI Density > 60%')
 
-    met1accum = sum(met1fill) / atotal
+    met1accum = 0
+    for y in range(0, ytiles - 1):
+        base = xtiles * y
+        met1accum += sum(met1fill[base:base + xtiles - 1])
+        met1accum += met1fill[base + xtiles - 1] * xfrac
+    base = xtiles * (ytiles - 1)
+    met1accum += sum(met1fill[base:base + xtiles - 1]) * yfrac
+    met1accum += met1fill[base + xtiles - 1] * xfrac * yfrac
+
+    met1accum /= atotal
+    met1str = "{:.3f}".format(met1accum)
     print('')
-    print('MET1 Density: ' + str(met1accum))
+    print('MET1 Density: ' + met1str)
     if met1accum < 0.35:
         print('***Error:  MET1 Density < 35%')
     elif met1accum > 0.60:
         print('***Error:  MET1 Density > 60%')
 
-    met2accum = sum(met2fill) / atotal
+    met2accum = 0
+    for y in range(0, ytiles - 1):
+        base = xtiles * y
+        met2accum += sum(met2fill[base:base + xtiles - 1])
+        met2accum += met2fill[base + xtiles - 1] * xfrac
+    base = xtiles * (ytiles - 1)
+    met2accum += sum(met2fill[base:base + xtiles - 1]) * yfrac
+    met2accum += met2fill[base + xtiles - 1] * xfrac * yfrac
+
+    met2accum /= atotal
+    met2str = "{:.3f}".format(met2accum)
     print('')
-    print('MET2 Density: ' + str(met2accum))
+    print('MET2 Density: ' + met2str)
     if met2accum < 0.35:
         print('***Error:  MET2 Density < 35%')
     elif met2accum > 0.60:
         print('***Error:  MET2 Density > 60%')
 
-    met3accum = sum(met3fill) / atotal
+    met3accum = 0
+    for y in range(0, ytiles - 1):
+        base = xtiles * y
+        met3accum += sum(met3fill[base:base + xtiles - 1])
+        met3accum += met3fill[base + xtiles - 1] * xfrac
+    base = xtiles * (ytiles - 1)
+    met3accum += sum(met3fill[base:base + xtiles - 1]) * yfrac
+    met3accum += met3fill[base + xtiles - 1] * xfrac * yfrac
+
+    met3accum /= atotal
+    met3str = "{:.3f}".format(met3accum)
     print('')
-    print('MET3 Density: ' + str(met3accum))
+    print('MET3 Density: ' + met3str)
     if met3accum < 0.35:
         print('***Error:  MET3 Density < 35%')
     elif met3accum > 0.60:
         print('***Error:  MET3 Density > 60%')
 
-    met4accum = sum(met4fill) / atotal
+    met4accum = 0
+    for y in range(0, ytiles - 1):
+        base = xtiles * y
+        met4accum += sum(met4fill[base:base + xtiles - 1])
+        met4accum += met4fill[base + xtiles - 1] * xfrac
+    base = xtiles * (ytiles - 1)
+    met4accum += sum(met4fill[base:base + xtiles - 1]) * yfrac
+    met4accum += met4fill[base + xtiles - 1] * xfrac * yfrac
+
+    met4accum /= atotal
+    met4str = "{:.3f}".format(met4accum)
     print('')
-    print('MET4 Density: ' + str(met4accum))
+    print('MET4 Density: ' + met4str)
     if met4accum < 0.35:
         print('***Error:  MET4 Density < 35%')
     elif met4accum > 0.60:
         print('***Error:  MET4 Density > 60%')
 
-    met5accum = sum(met5fill) / atotal
+    met5accum = 0
+    for y in range(0, ytiles - 1):
+        base = xtiles * y
+        met5accum += sum(met5fill[base:base + xtiles - 1])
+        met5accum += met5fill[base + xtiles - 1] * xfrac
+    base = xtiles * (ytiles - 1)
+    met5accum += sum(met5fill[base:base + xtiles - 1]) * yfrac
+    met5accum += met5fill[base + xtiles - 1] * xfrac * yfrac
+
+    met5accum /= atotal
+    met5str = "{:.3f}".format(met5accum)
     print('')
-    print('MET5 Density: ' + str(met5accum))
+    print('MET5 Density: ' + met5str)
     if met5accum < 0.45:
         print('***Error:  MET5 Density < 45%')
     elif met5accum > 0.76:
         print('***Error:  MET5 Density > 76%')
 
     if not keepmode:
-        if os.path.isfile(gdspath + '/check_density.tcl'):
-            os.remove(gdspath + '/check_density.tcl')
+        if os.path.isfile(layoutpath + '/check_density.tcl'):
+            os.remove(layoutpath + '/check_density.tcl')
 
     print('')
     print('Done!')
diff --git a/sky130/custom/scripts/generate_fill.py b/sky130/custom/scripts/generate_fill.py
index 38ecc39..1d08dad 100755
--- a/sky130/custom/scripts/generate_fill.py
+++ b/sky130/custom/scripts/generate_fill.py
@@ -24,6 +24,7 @@
 import os
 import re
 import glob
+import functools
 import subprocess
 import multiprocessing
 
@@ -32,31 +33,37 @@
     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("    <layout_name> is the path to the .mag or .gds 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):
+def makegds(file, rcfile):
     # 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]
+    layoutpath = 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],
+    magic_run_opts = [
+		'magic',
+		'-dnull',
+		'-noconsole',
+		'-rcfile', rcfile,
+		'generate_fill_dist.tcl',
+		filename]
+
+    mproc = subprocess.run(magic_run_opts,
 		stdin = subprocess.DEVNULL,
 		stdout = subprocess.PIPE,
 		stderr = subprocess.PIPE,
-		cwd = magpath,
+		cwd = layoutpath,
 		env = myenv,
 		universal_newlines = True)
     if mproc.stdout:
@@ -91,57 +98,111 @@
         usage()
         sys.exit(1)
 
+    # Process options
+
+    if '-debug' in optionlist:
+        debugmode = True
+        print('Running in debug mode.')
+    if '-keep' in optionlist:
+        keepmode = True
+        if debugmode:
+            print('Keeping all files after running.')
+    elif debugmode:
+        print('Files other than final layout will be removed after running.')
+    if '-test' in optionlist:
+        testmode = True
+        if debugmode:
+            print('Running in test mode:  No output files will be created.')
+    if '-dist' in optionlist:
+        distmode = True
+        if debugmode:
+            print('Running in distributed (multi-processing) mode.')
+    elif debugmode:
+        print('Running in single-processor mode.')
+
+    # Find layout from command-line argument
+
     user_project_path = arguments[0]
 
-    magpath = os.getcwd()+'/'+os.path.split(user_project_path)[0]
-    if magpath == '':
-        magpath = os.getcwd()
-    
-    if os.path.splitext(user_project_path)[1] != '.mag':
-        if os.path.splitext(user_project_path)[1] == '':
-            user_project_path += '.mag'
-        else:
-            print('Error:  Project is not a magic database .mag file!')
+    if os.path.split(user_project_path)[0] == '':
+        layoutpath = os.getcwd()
+    else:
+        layoutpath = os.getcwd() + '/' + os.path.split(user_project_path)[0]
+
+    # Use os.extsep, not os.path.splitext(), because gzipped files have
+    # multiple periods (e.g., "layout.gds.gz")
+
+    project = user_project_path.split(os.extsep, 1)
+
+    if len(project) == 1:
+        # No file extension given;  figure it out
+        layoutfiles = glob.glob(user_project_path + '.*')
+        if len(layoutfiles) == 1:
+            proj_extension = '.' + layoutfiles[0].split(os.extsep, 1)[1]
+            user_project_path = layoutfiles[0]
+        elif len(layoutfiles) == 0:
+            print('Error:  Project is not a magic database or GDS file!')
             sys.exit(1)
+        else:
+            print('Error:  Project name is ambiguous!')
+            sys.exit(1)
+    else:
+        proj_extension = '.' + project[1]
+
+    is_mag = False
+    is_gds = False
+
+    if proj_extension == '.mag' or proj_extension == '.mag.gz':
+        is_mag = True
+    elif proj_extension == '.gds' or proj_extension == '.gds.gz':
+        is_gds = True
+    else:
+        print('Error:  Project is not a magic database or GDS file!')
+        sys.exit(1)
 
     if not os.path.isfile(user_project_path):
         print('Error:  Project "' + user_project_path + '" does not exist or is not readable.')
         sys.exit(1)
 
-    if '-debug' in optionlist:
-        debugmode = True
-    if '-keep' in optionlist:
-        keepmode = True
-    if '-test' in optionlist:
-        testmode = True
-    if '-dist' in optionlist:
-        distmode = True
+    # The path where the fill generation script resides should be the same
+    # path where the magic startup script resides, for the same PDK
+    scriptpath = os.path.dirname(os.path.realpath(__file__))
 
-    # Searching for rcfile
-    
-    rcfile_paths=[magpath+'/.magicrc','/$PDK_PATH/libs.tech/magic/TECHNAME.magicrc','/usr/share/pdk/TECHNAME/libs.tech/magic/TECHNAME.magicrc']
-    
-    rcfile=''
-    
-    for rc_path in rcfile_paths:
-        if os.path.isfile(rc_path):
-            rcfile=rc_path
-            break
-    
-    if rcfile=='':
-        print('Error: .magicrc file not found.')
+    # Search for magic startup script.  Order of precedence:
+    #  1. PDK_ROOT environment variable
+    #  2. Local .magicrc
+    #  3. The location of this script
+
+    if os.environ.get('PDK'):
+        pdk_name = os.environ.get('PDK')
+    else:
+        pdk_name = 'sky130A'
+
+    if os.environ.get('PDK_ROOT'):
+        rcfile_path = os.environ.get('PDK_ROOT') + '/' + pdk_name + '/libs.tech/magic/' + pdk_name + '.magicrc'
+    elif os.path.isfile(layoutpath + '/.magicrc'):
+        rcfile_path = layoutpath + '/.magicrc'
+    elif os.path.isfile(scriptpath + '/' + pdk_name + '.magicrc'):
+        rcfile_path = scriptpath + '/' + pdk_name + '.magicrc'
+    else:
+        print('Unknown path to magic startup script.  Please set $PDK_ROOT')
         sys.exit(1)
-    
-    project = os.path.splitext(os.path.split(user_project_path)[1])[0]
 
-    topdir = os.path.split(magpath)[0]
-    gdsdir = topdir + '/gds'
-    hasgdsdir = True if os.path.isdir(gdsdir) else False
-    
-    ofile = open(magpath + '/generate_fill.tcl', 'w') 
+    if os.path.isdir(layoutpath + '/gds'):
+        gdspath = layoutpath + '/gds'
+    elif os.path.isdir(layoutpath + '/../gds'):
+        gdspath = layoutpath + '/../gds'
+    else:
+        gdspath = layoutpath
+
+    project_file = os.path.split(user_project_path)[1]
+    project = project_file.split(os.extsep, 1)[0]
+
+    ofile = open(layoutpath + '/generate_fill.tcl', 'w') 
 	
     print('#!/usr/bin/env wish', file=ofile)
     print('drc off', file=ofile)
+    print('crashbackups stop', file=ofile)
     print('tech unlock *', file=ofile)
     print('snap internal', file=ofile)
     print('box values 0 0 0 0', file=ofile)
@@ -153,12 +214,18 @@
     print('set starttime [orig_clock format [orig_clock seconds] -format "%D %T"]', file=ofile)
     print('puts stdout "Started: $starttime"', file=ofile)
     print('', file=ofile)
+    if is_gds:
+        print('gds read ' + project_file, file=ofile)
+    # NOTE:  No guarantee that the filename matches the top level cell name;
+    # might want to query using "cellname list top"
     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)
+    # Use FIXED_BBOX as the boundary if it exists
+    print('catch {box values {*}[property FIXED_BBOX]}', 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)
@@ -234,7 +301,7 @@
         print('quit -noprompt', file=ofile)
         ofile.close()
 
-        with open(magpath + '/generate_fill_dist.tcl', 'w') as ofile:
+        with open(layoutpath + '/generate_fill_dist.tcl', 'w') as ofile:
             print('#!/usr/bin/env wish', file=ofile)
             print('drc off', file=ofile)
             print('tech unlock *', file=ofile)
@@ -246,7 +313,7 @@
             print('gds write [file root $filename].gds', file=ofile)
             print('quit -noprompt', file=ofile)
 
-        ofile = open(magpath + '/generate_fill_final.tcl', 'w')
+        ofile = open(layoutpath + '/generate_fill_final.tcl', 'w')
         print('#!/usr/bin/env wish', file=ofile)
         print('drc off', file=ofile)
         print('tech unlock *', file=ofile)
@@ -272,7 +339,7 @@
     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}_$y -quiet', file=ofile)
+    print('        load ' + project + '_fill_pattern_${x}_$y -silent', 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)
@@ -282,7 +349,7 @@
     print('}', file=ofile)
 
     # Now tile everything back together
-    print('load ' + project + '_fill_pattern -quiet', file=ofile)
+    print('load ' + project + '_fill_pattern -silent', 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)
@@ -295,10 +362,8 @@
 
     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('gds compress 9', file=ofile)
+    print('gds write ' + gdspath + '/' + project + '_fill_pattern.gds.gz', 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)
@@ -309,16 +374,25 @@
 
     if not testmode:
         # Diagnostic
-        # print('This script will generate file ' + project + '_fill_pattern.gds')
+        # print('This script will generate file ' + project + '_fill_pattern.gds.gz')
         print('This script will generate files ' + project + '_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'],
+        magic_run_opts = [
+		'magic',
+		'-dnull',
+		'-noconsole',
+		'-rcfile', rcfile_path,
+		'generate_fill.tcl']
+
+        if debugmode:
+            print('Running: ' + ' '.join(magic_run_opts))
+
+        mproc = subprocess.run(magic_run_opts,
 		stdin = subprocess.DEVNULL,
 		stdout = subprocess.PIPE,
 		stderr = subprocess.PIPE,
-		cwd = magpath,
+		cwd = layoutpath,
 		env = myenv,
 		universal_newlines = True)
         
@@ -337,24 +411,31 @@
             # 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')
+            magfiles = glob.glob(layoutpath + '/' + 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)
+            makegdsfunc = functools.partial(makegds, rcfile=rcfile_path)
+            pool.map(makegdsfunc, 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'],
+            magic_run_opts = [
+			'magic',
+			'-dnull',
+			'-noconsole',
+			'-rcfile', rcfile_path,
+			'generate_fill_final.tcl']
+
+            mproc = subprocess.run(magic_run_opts,
 			stdin = subprocess.DEVNULL,
 			stdout = subprocess.PIPE,
 			stderr = subprocess.PIPE,
-			cwd = magpath,
+			cwd = layoutpath,
 			env = myenv,
 			universal_newlines = True)
             if mproc.stdout:
@@ -369,20 +450,20 @@
 
     if not keepmode:
         # Remove fill generation script
-        os.remove(magpath + '/generate_fill.tcl')
+        os.remove(layoutpath + '/generate_fill.tcl')
         # Remove all individual fill tiles, leaving only the composite GDS.
-        filelist = os.listdir(magpath)
+        filelist = os.listdir(layoutpath)
         for file in filelist:
-            if os.path.splitext(magpath + '/' + file)[1] == '.gds':
+            if os.path.splitext(layoutpath + '/' + file)[1] == '.gds':
                 if file.startswith(project + '_fill_pattern_'):
-                    os.remove(magpath + '/' + file)
+                    os.remove(layoutpath + '/' + file)
 
         if distmode:
-            os.remove(magpath + '/generate_fill_dist.tcl')
-            os.remove(magpath + '/generate_fill_final.tcl')
-            os.remove(magpath + '/fill_gen_info.txt')
+            os.remove(layoutpath + '/generate_fill_dist.tcl')
+            os.remove(layoutpath + '/generate_fill_final.tcl')
+            os.remove(layoutpath + '/fill_gen_info.txt')
             if testmode:
-                magfiles = glob.glob(magpath + '/' + project + '_fill_pattern_*.mag')
+                magfiles = glob.glob(layoutpath + '/' + project + '_fill_pattern_*.mag')
                 for file in magfiles:
                     os.remove(file)