Added recipes to the Makefiles to execute "make update", which
visits all directories in source/ that are git repositories and
runs "git pull". Also: Removed the recipe for installing the
xschem sky130 library, and added a new one which reflects recent
changes in the repository supporting the PDK_ROOT environment
variable and supporting the reram device in sky130B. Properly
resolved differences in xschem's setup for sky130A vs. sky130B.
diff --git a/sky130/custom/scripts/pdk_update.sh b/sky130/custom/scripts/pdk_update.sh
new file mode 100755
index 0000000..47910b2
--- /dev/null
+++ b/sky130/custom/scripts/pdk_update.sh
@@ -0,0 +1,31 @@
+#!/bin/sh
+#
+# pdk_update.sh --
+#
+# Update the PDK from git
+# (mainly for use with the Google/SkyWater SKY130 PDK)
+#
+# Usage: pdk_update.sh <directory>
+#
+
+if [ ! test -d $1 ] ; then
+ echo "Project does not exist in $pdir ; Cannot update."
+ exit 0
+fi
+
+cd $1
+
+# Update top-level PDK repository
+
+echo "Pulling PDK repository"
+git pull
+
+# Update submodules
+
+echo "Updating PDK library submodules"
+git submodule update --remote
+
+# Regenerate liberty files
+
+echo "Regenerating liberty timing files"
+make timing
