Assume I have a vehicle containing a screen that is connected to the vehicles can-bus and that the screen is using the android automotive OS. Disregard Google play store. Is it possible to create a third party app for android automotive that can read and send can-packets directly to the can-bus? The purpose is controlling physical third party addons connected to the can-bus, not to access functions already used by the vehicle like accelleration, engine-state and so on.
Direct access to can-bus is not possible. Android Automotive uses Vehicle HAL - Vehicle HAL is a lower layer that interacts with the vehicle, communicating with in-vehicle networks and other vehicular hardware.
Also, access to VHAL is restricted to system application.
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The vehicle HAL is the only component in Android Automotive connected to the IVI system, either via direct Application Processor/MicroController connection or gated through a VMCU. Access to the Vehicle HAL should be restricted to system applications using SELinux rules and proper permissions on kernel interfaces.
PTAL https://developer.android.com/reference/android/car/VehiclePropertyIds for more detail.