MSFS2020 SimConnect

Behavior during startup

After beginning the startup of the simulator, no SimConnect connection is possible. At some point A in the loading sequence, the SimConnect endpoint becomes available for clients. But at first all messages sent by an external process or a WASM standalone module are queued for a certain period (e.g 10 to 20 seconds). No message is processed, including SimConnect_Open. That delay ensures that components and modules can finish initialization before general SimConnect processing starts. At some later point B in time the processing starts and at first the queued messages are processed. During that processing also SimConnect_Open is processed and the clients receive their SimConnect_OnRecvOpen callbacks.

Sequence:

• 0: Startup of simulator begins
• Load packages, parse Material.xml
• A: Simconnect endpoint becomes available (but incoming messages are saved and queued)
• Initialize WASM modules and simulator components
• B: Simconnect message processing starts (and SimConnect_OnRecvOpen callbacks are sent)
• Read libraries, load gltf files and behavior XML
• Startup complete

References:

• https://devsupport.flightsimulator.com/t/is-standalone-wasm-initialized-before-external-simconnect-becomes-available/6535/2
• Analyze verbose SimConnect traces: https://docs.flightsimulator.com/html/Programming_Tools/SimConnect/SimConnect_INI_Definition.htm