Corrected an error in the GF library where an incorrect entry in
the custom digital bidirectional I/O cell caused the liberty file
for both the original GF library and the custom extension to be
incorrect.  Also:  Updated the README file with more complete
information, including information and instructions on GF180MCU,
which had never been added;  and comments about the IHP open PDK
and about the "ciel" PDK package manager.
diff --git a/README.md b/README.md
index 25feb5c..eca50c1 100644
--- a/README.md
+++ b/README.md
@@ -6,11 +6,11 @@
 Automatic setup of PDKs for open-source tools from foundry sources.
 
 Builds out and populates a new set of directories and subdirectories in
-the efabless format, with the efabless name for the PDK at the top,
-followed by categories "libs.ref" (IP) and "libs.tech" (EDA tool setup),
-each with subcategories corresponding to layout, abstract views,
-netlists, etc. for the IP;  and magic, netgen, qflow, etc., for the
-EDA tool setup.
+the open source format (started by Efabless), with the name for the PDK
+at the top, followed by categories "libs.ref" (IP) and "libs.tech"
+(EDA tool setup), each with subcategories corresponding to layout,
+abstract views, netlists, etc. for the IP;  and magic, netgen, qflow,
+etc., for the EDA tool setup.
 
 The populated PDK directories can contain either copies of files from
 the foundry sources, links to the foundry sources, or links back to
@@ -23,9 +23,17 @@
 -----------------------------------------
 
 This distribution contains sources for building out the SkyWater SKY130
-130nm process.  Sources for the foundry process data must be obtained
-separately.  Read the README file in subdirectory sky130/ for instructions
-on obtaining and building the SkyWater sky130A PDK.
+130nm process and the GlobalFoundries GF180MCU process.  Sources for the
+foundry process data are cloned automatically from repository services
+(primarily github).
+
+Other non-free processes (such as X-Fab XH035 or XH018) can be obtained
+as "plug-ins" for open_pdks.  Sources for non-free foundry process data
+must be obtained separately.
+
+Read the README file in subdirectory sky130/ for instructions on building
+the SkyWater sky130A PDK, or in the directory gf180mcu/ for instructions
+on building the GlobalFoundries gf180MCU PDK.
 
 -----------------------------------------
 
@@ -36,6 +44,51 @@
 
 -----------------------------------------
 
+"Ciel" package manager:
+
+An important consideration for anyone wishing to obtain one of the open
+source PDKs is that "open_pdks" is a PDK builder, and running it is like
+running a compiler to build a complex software application.  Doing so
+can be difficult, time consuming, and resource-intensive.  The software
+world came up with the idea of a "package manager" application that
+handles pre-built software.  Likewise, there is a "PDK package manager"
+for handling pre-built PDKs, called "ciel" (formerly called "volare"),
+which can be found at https://github.com/fossi-foundation/ciel;
+However, "ciel" can be installed simply by doing:
+
+	pip install ciel
+
+Most PDK end-users are likely to want this option.  The "pip install"
+command will put "ciel" in ~/.local/bin/ciel where it may be necessary
+to either call it with the full path on the command line, or you may
+need to add "~/.local/bin" to your PATH environment variable.  Assuming
+it is in PATH, use the following commands:
+
+	ciel ls-pdks
+
+returns a list of processes supported by ciel.  To get a list of
+pre-built PDKs, use, e.g.,
+
+	ciel ls-remote --pdk-family=sky130
+
+which lists PDKs by commit hash number.  Then to install the PDK, use, e.g.,
+
+	ciel enable --pdk-family=sky130 <commit_hash>
+
+The PDK will be installed into directory ~/.ciel/.  Most open source
+EDA tools will be able to find the PDK if the environment variable
+"PDK_ROOT" is set to point to this location:
+
+	export PDK_ROOT=~/.ciel
+
+for bash/sh environments, and
+
+	setenv PDK_ROOT ~/.ciel
+
+for csh/tcsh environments.
+
+-----------------------------------------
+
 Instructions:
 
     git clone https://github.com/RTimothyEdwards/open_pdks.git
@@ -70,3 +123,47 @@
 Also see the website at http://opencircuitdesign.com/open_pdks/.  The "Install"
 page has full instructions for configuring and installing open_pdks.
 
+-----------------------------------------
+
+Example usage:
+
+    SkyWater sky130 PDK:
+
+	./configure --prefix=/usr --enable-sky130-pdk --enable-sram-sky130 \
+		--enable-sram-space-sky130 --enable-reram-sky130
+	make
+	sudo make install
+
+    GlobalFoundries GF180MCU PDK:
+
+	./configure --prefix=/usr --enable-gf180mcu-pdk
+	make
+	sudo make install
+
+    Both of these examples install into the directory /usr/share/pdk/.
+    The first one builds PDKs sky130A (standard) and sky130B (with the
+    ReRAM option).  The second one builds PDKs gf180mcuA (3 metal stack),
+    gf180mcuB (4 metal stack), gf180mcuC (5 metal stack with 0.9um thick
+    top metal), and gf180mcuD (5 metal stack with 1.1um thick top metal).
+
+    Existing shuttle services as of this writing (September 2025) use
+    sky130A, sky130B (Cadence, Chip Foundry), and gf180mcuD
+    (Wafer.Space).
+
+    Given the configurations above with prefix "/usr", most open source
+    tools will expect
+
+	export PDK_ROOT=/usr/share/pdk		(sh, bash)
+    or
+	setenv PDK_ROOT /usr/share/pdk		(csh, tcsh)
+
+-----------------------------------------
+
+A note about IHP SG13G2:
+
+    IHP GmbH released their open PDK for the SG13G2 process using
+    the format described in open_pdks.  For this reason, there is
+    no need to use open_pdks to build the IHP open PDK, because it
+    already comes pre-built, with full support for open source EDA
+    tools.  Also for this reason, the SG13G2 open PDK is supported
+    by the "ciel" PDK package manager (see above).
diff --git a/VERSION b/VERSION
index 2cc2aa0..c313ca4 100644
--- a/VERSION
+++ b/VERSION
@@ -1 +1 @@
-1.0.540
+1.0.541
diff --git a/docs.txt b/docs.txt
index f463899..775c185 100644
--- a/docs.txt
+++ b/docs.txt
@@ -3,7 +3,7 @@
 
 ----------------------------------------------------------------------------------
 
-Written by Tim Edwards 2019 - 2022 for efabless (efabless.com)
+Written by Tim Edwards 2019 - 2025 for efabless (efabless.com)
 and Open Circuit Design (opencircuitdesign.com)
 
 URL: http://opencircuitdesign.com/open_pdks
@@ -15,9 +15,10 @@
 
 Quick Install:
 
-    Looking to install the Google/SkyWater SKY130 PDK libraries and setup
-    files for open source EDA tools?  Read the README file in the sky130/
-    directory.
+    Looking to install the Google/SkyWater SKY130 PDK or the
+    Google/GlobalFoundries GF180MCU PDK libraries and setup
+    files for open source EDA tools?  Read the README.md file or the
+    README file in the sky130/ or gf180mcu/ directories.
 
     The rest of this README file is general information about open_pdks
     and is not specific to any single PDK.
diff --git a/gf180mcu/custom/gf180mcu_fd_io/lib/gf180mcu_ef_io__bi_t__ff_125C_2v75.lib b/gf180mcu/custom/gf180mcu_fd_io/lib/gf180mcu_ef_io__bi_t__ff_125C_2v75.lib
index 9a3416f..bb9c616 100644
--- a/gf180mcu/custom/gf180mcu_fd_io/lib/gf180mcu_ef_io__bi_t__ff_125C_2v75.lib
+++ b/gf180mcu/custom/gf180mcu_fd_io/lib/gf180mcu_ef_io__bi_t__ff_125C_2v75.lib
@@ -13,7 +13,7 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
-	cell ("gf180mcu_fd_io__bi_t") {
+	cell ("gf180mcu_ef_io__bi_t") {
 		scaling_factors : "gf_factors";
 		area : 26250.000000;
 		pad_cell : true;