Limited release of the SKY130 IO and periphery cells.

Release of a subset of the full IO. This release includes;
 * Power pads;
    - High voltage - `top_power_hvc_wpad`, `top_ground_hvc_wpad`
    - Low voltage - `top_power_lvc_wpad`, `top_ground_lvc_wpad`
 * Reference generators - `top_refgen`, `top_refgen_new`.
 * Standard GPIO (`top_gpiov2`).
 * I2C compatible GPIO with over-voltage tolerance (`top_gpio_ovtv2`).
 * Special SIO (`top_sio`) with differential macro (`top_sio_macro`).
 * System wide reset influencing XRES cell (`top_xres4v2`).

Future release will include;
 * Original standard GPIO (`top_gpio`).
 * More power pad versions.
 * More XRES cells.
 * More reference generators (`top_vrefcapv2`, etc).
 * Spice and CDL models for the IOs.

Signed-off-by: Tim 'mithro' Ansell <me@mith.ro>

.gitmodules

@@ -156,3 +156,41 @@
 	branch = branch-0.1.0
 	shallow = true
 	fetchRecurseSubmodules = false
+
+# sky130_fd_io
+[submodule "libraries/sky130_fd_io/latest"]
+	path = libraries/sky130_fd_io/latest
+	url = https://foss-eda-tools.googlesource.com/skywater-pdk/libs/sky130_fd_io.git
+	branch = master
+	shallow = true
+	fetchRecurseSubmodules = true
+[submodule "libraries/sky130_fd_io/v0.2.1"]
+	path = libraries/sky130_fd_io/v0.2.1
+	url = https://foss-eda-tools.googlesource.com/skywater-pdk/libs/sky130_fd_io.git
+	branch = branch-0.2.1
+	shallow = true
+	fetchRecurseSubmodules = false
+[submodule "libraries/sky130_fd_io/v0.2.0"]
+	path = libraries/sky130_fd_io/v0.2.0
+	url = https://foss-eda-tools.googlesource.com/skywater-pdk/libs/sky130_fd_io.git
+	branch = branch-0.2.0
+	shallow = true
+	fetchRecurseSubmodules = false
+[submodule "libraries/sky130_fd_io/v0.1.0"]
+	path = libraries/sky130_fd_io/v0.1.0
+	url = https://foss-eda-tools.googlesource.com/skywater-pdk/libs/sky130_fd_io.git
+	branch = branch-0.1.0
+	shallow = true
+	fetchRecurseSubmodules = false
+[submodule "libraries/sky130_fd_io/v0.0.2"]
+	path = libraries/sky130_fd_io/v0.0.2
+	url = https://foss-eda-tools.googlesource.com/skywater-pdk/libs/sky130_fd_io.git
+	branch = branch-0.1.0
+	shallow = true
+	fetchRecurseSubmodules = false
+[submodule "libraries/sky130_fd_io/v0.0.1"]
+	path = libraries/sky130_fd_io/v0.0.1
+	url = https://foss-eda-tools.googlesource.com/skywater-pdk/libs/sky130_fd_io.git
+	branch = branch-0.0.1
+	shallow = true
+	fetchRecurseSubmodules = false

libraries/sky130_fd_io/latest

@@ -0,0 +1 @@
+Subproject commit 01b18699b4102d8e54ad1406b3991ecb652e5aee

libraries/sky130_fd_io/latest/README.rst

@@ -1,10 +0,0 @@
-:lib:`sky130_fd_io` - SKY130 IO and periphery cells (SkyWater Provided)
-=======================================================================
-
-Initial documentation only release.
-
-.. toctree::
-    :maxdepth: 1
-    :name: sky130-lib-foundry-io-top
-
-    docs/user_guide

libraries/sky130_fd_io/v0.0.1

@@ -0,0 +1 @@
+Subproject commit e89f551c5b934870b1eeef1898d410554713fb74

libraries/sky130_fd_io/v0.0.2

@@ -0,0 +1 @@
+Subproject commit 4048fc6e03b5a246a1287777ac4f0e4a99ef484f

libraries/sky130_fd_io/v0.1.0

@@ -0,0 +1 @@
+Subproject commit 40adf19b0baa59da5fb0b8b8b63d0e52dc8697c6

libraries/sky130_fd_io/v0.2.0

@@ -0,0 +1 @@
+Subproject commit 80ef9b27e7e677f4c0e9f9ee39ea94b9cd261f39

libraries/sky130_fd_io/v0.2.1

@@ -0,0 +1 @@
+Subproject commit 01b18699b4102d8e54ad1406b3991ecb652e5aee