diff --git a/doc/README.md b/doc/README.md
index 7ce14c9..04e4de5 100644
--- a/doc/README.md
+++ b/doc/README.md
@@ -18,7 +18,8 @@ Table of contents:
   * [popnhook](popnhook/README.md): Documentation relevant to `popnhook` implementations
   * [sdvxhook](sdvxhook/README.md): Documentation relevant to `sdvxhook` implementations
 * Development
-  * [API](api.md): Available APIs for BT5 and instructions how to use them
+  * [API](api.md): Available APIs and IO (hardware) implementations for BT5 and instructions how
+    to use them
   * [Architecture](architecture.md): Outline of BT5's architecture, how things are designed and why
   * [Development](development.md): Development environment, building, releasing, etc.
   * [Developer documentation](dev/README.md): Various lose documentation/notes by developers
diff --git a/doc/api.md b/doc/api.md
index 3c85111..605735a 100644
--- a/doc/api.md
+++ b/doc/api.md
@@ -25,6 +25,8 @@ The following implementations are already shipped with BT5.
     * [ddrio-p3io.dll](ddrhook/ddrio-p3io.md): DDR P3IO (Dragon PCB) + EXTIO hardware
     * ddrio-mm.dll: Minimaid hardware
     * [ddrio-smx.dll](ddrhook/ddrio-smx.md): StepManiaX platforms
+    * [ddrio-async](ddrhook/ddrio-async.md): Wrapper/shim library to drive another ddrio in
+      a dedicated IO thread
 * Beatmania IIDX
     * iidxio.dll (default): Keyboard, joystick and mouse input
     * [iidxio-bio2.dll](iidxhook/iidxio-bio2.md): BIO2 driver
diff --git a/doc/ddrhook/README.md b/doc/ddrhook/README.md
index cb4b763..3b94179 100644
--- a/doc/ddrhook/README.md
+++ b/doc/ddrhook/README.md
@@ -46,7 +46,10 @@ IO hardware you want to use:
 * `ddrio`: Default implementation supporting keyboard, mouse and USB
 game controllers
 * ddrio-mm: Support Minimaid custom interface
-* [ddrio-smx](ddrhook/ddrio-smx.md): Support for StepManiaX dance platforms
+* [ddrio-smx](ddrio-smx.md): Support for StepManiaX dance platforms
+* [ddrio-p3io](ddrio-p3io.md): P3IO + EXTIO driver implementation
+* [ddrio-async](ddrio-async.md): Wrapper/shim library to drive another ddrio in
+  a dedicated IO thread
 
 ## Unicorntail
 
diff --git a/doc/ddrhook/ddrio-async.md b/doc/ddrhook/ddrio-async.md
new file mode 100644
index 0000000..d0ac931
--- /dev/null
+++ b/doc/ddrhook/ddrio-async.md
@@ -0,0 +1,36 @@
+# Asynchronous proxy wrapper for other ddrio implementations
+
+This implementation of the Bemanitools API is not implementing support for any
+specific IO hardware. It is a proxy/shim library that loads another ddrio
+library, e.g. ddrio-p3io, and drives the entire backend in a dedicated IO
+thread. By implementing this behind the ddrio API, it is fully transparent to
+any existing application using it.
+
+The main benefit is the improved IO polling performance depending on how
+expensive the synchronous calls of the actual hardware are. For example,
+*ddrio-p3io* has very expensive write calls with ~12 ms duration while read
+calls take ~4 ms. Therefore, a full update cycle is already about as costly
+as rendering an entire frame (at 60 fps).
+
+## Setup
+
+For hook libraries, i.e. ddrhookX, but likely applicable to 3rd party
+applications (consolidate their manuals).
+
+* Have `ddrio-async.dll` in the same folder as your `ddrhookX.dll`
+* Rename `ddrio-async.dll` to `ddrio.dll`
+* Pick another ddrio library as the backend of your choice, e.g. `ddrio-p3io.dl`
+  and put it next to the async `ddrio.dll`
+* Rename it to `ddrio-async-child.dll`, ddrio-async is looking for that filename
+  in the same folder
+* Ensure that your `gamestart.bat` actually injects the appropriate `ddrhook.dll`, for example:
+
+```bat
+inject ddrhook1.dll ddr.exe ...*
+```
+
+or
+
+```bat
+launcher -K ddrhook2.dll arkmdxp3.dll ...*
+```
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