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+## Communication
+
+The client and the app communicate through several shared-memory message-passing channels:
+
+### Messages from client to app
+
+#### process_control_request
+```xml
+
+
+
+
+
+
+```
+#### heartbeat
+```xml
+
+
+
+
+```
+
+#### trickle_down
+```xml
+
+```
+#### graphics_request
+
+Not used
+
+### Messages from app to client
+
+#### app_status
+```xml
+...
+...
+...
+ ...
+```
+
+#### trickle_up
+
+```xml
+
+```
+
+#### process_control_reply
+
+Not used
+
+#### graphics_reply
+```xml
+
+
+```