docs/2_waltham-receiver_waltham-transmitter: Added waltham documentation

Bug-AGL: SPEC-3777

Signed-off-by: Marius Vlad <marius.vlad@collabora.com>
Change-Id: I022c24b18b247df97f0c5781545e1ffb06656e3e
Reviewed-on: https://gerrit.automotivelinux.org/gerrit/c/AGL/documentation/+/26137
Tested-by: Jan-Simon Moeller <jsmoeller@linuxfoundation.org>
Reviewed-by: Jan-Simon Moeller <jsmoeller@linuxfoundation.org>

1 files changed, 91 insertions, 2 deletions

diff --git a/docs/5_Component_Documentation/2_waltham-receiver_waltham-transmitter.md b/docs/5_Component_Documentation/2_waltham-receiver_waltham-transmitter.md
index cfaaf7b..b98de32 100644
--- a/docs/5_Component_Documentation/2_waltham-receiver_waltham-transmitter.md
+++ b/docs/5_Component_Documentation/2_waltham-receiver_waltham-transmitter.md
@@ -2,6 +2,95 @@
 title: Waltham receiver/transmitter
 ---
 
-# waltham
+# Waltham
 
-FIXME.
+[Waltham protocol](https://github.com/waltham/waltham) is a IPC library similar
+to [Wayland](https://wayland.freedesktop.org), developed with networking in
+mind. It operates over TCP sockets, while the wayland protocol only works
+locally over a UNIX socket. It retains wayland-esque paradigm, making use of
+XMLs to describe the protocol, and it follows an object-oriented design with an
+asynchronous architecture.
+
+## Differences from Wayland to Waltham
+
+Some of the differences between Wayland and Waltham are:
+
+* Waltham uses TCP sockets for communication
+* Waltham cannot send file descriptors
+* Waltham API is minimal and symmetric between server and client sides
+* Waltham does not provide an event loop implementation
+* The registry implementation is left out of the library, only the interface is
+  provided
+* No multi-threading support for sharing objects between threads
+
+## Waltham-transmitter and remoting plugin
+
+Surface sharing is not part of Waltham protocol, each system needs to implement
+the most efficient way of passing by the buffers from one side to another.  On
+AGL, make use of remoting-plugin to enable surface sharing which uses GStreamer
+as encoder/decoder. It uses libweston DRM virtual API to grab the buffers, and
+then to stream them over the network. The gstreamer pipeline uses UDP while the
+input events are communicated with Waltham protocol. The input part is handled
+by *waltham-transmitter* plugin which provides an API to create remote
+connections and push surfaces over the network and handles remote input. The
+act of pushing surface is a misnomer, kept from the older, previous
+implementation, and acts a notification mechanism from the transmitter side to
+the remote side.
+
+## The receiver client
+
+waltham-receiver application is a wayland demo implementation  which should be
+running at the remote side. It is using Waltham protocol to obtain and process
+remote input events which handled the transmitter side by the waltham-transmitter
+plugin. It creates a similar gstreamer pipeline to process the incoming buffers
+and draw and displaying them into a subsurface created by waylandsink.
+
+Contrary to expectations, the waltham receiver is the one that implements the
+server side of the Waltham protocol and is capable of displaying the incoming
+buffers but also process input events locally and forward them with the help of
+the Waltham protocol back at the transmitter side, which in turn will update
+the image contents and stream to the receiver, showing the changes caused by
+that input. 
+
+
+     ECU 1                                                               ECU 2
+     +---------------------------------------------+                    +--------------------------------------+
+     |        +-----------------+                  |                    |                                      |
+     |        |     Application |                  |                    |       +-----------+-----------+      |
+     |        +-----------------+                  |                    |       | Gstreamer |           |      |
+     |                 ^                           |    Buffer   ---------------> (Decode)  |           |      |
+     |        wayland  |                    +-------------------/       |       +-----------+           |      |
+     |                 v                    |      |    (Ethernet)      |       |     Waltham-receiver  |      |
+     |   +----+---------------------+       |      |        -------------------->                       |      |
+     |   |    |  Transmitter plugin |<---------------------/            |       +-----------------------+      |
+     |   |    |                     |       |      |  Waltham-Protocol  |                     ^                |
+     |   |    |---------------------|       |      |                    |             wayland |                |
+     |   |    |  Remoting plugin    |-------+      |                    |                     v                |
+     |   |    |                     |              |                    |         +---------------------+      |
+     |   |    +---------------------+              |                    |         |                     |      |
+     |   |                          |              |                    |         |       compositor    |      |
+     |   |         compositor       |              |                    |         |                     |      |
+     |   +------+-------------------+              |                    |         +----------------+----+      |
+     |          |                                  |                    |                          |           |
+     |          v                                  |                    |                          v           |
+     |   +------------+                            |                    |                    +----------+      |
+     |   |  Display   |                            |                    |                    |  Display |      |
+     |   |            |                            |                    |                    |          |      |
+     |   +------------+                            |                    |                    +----------+      |
+     +---------------------------------------------+                    +--------------------------------------+
+
+## Migrating/Placing applications on other outputs
+
+In order to start or place an application on the remoting-ouput output, we can
+use `agl-shell-app-id` ini entry for that particular output.
+
+	[transmitter-output]
+    name=transmitter-1
+    mode=640x720@30
+    host=192.168.20.99
+    port=5005
+    agl-shell-app-id=<APP_ID>
+
+Alternatively, and programmatically, one can use the
+[agl-shell-desktop](1_agl-compositor.md#private-extensions) protocol and inform
+the compositor that it should migrate it to other, remote outputs.