There are CarPlay resources from Apple (https://developer.apple.com/documentation/carplay/) but it seems entirely geared towards iOS app development.
Are there any resources or documentation that help with CarPlay integration on the vehicle/head unit side of things? I believe you need to download the CarPlay Communication Plug-In and integrate that with the head unit platform and applications, but there isn't much documentation that comes along with the Plug-In .zip download.
Is there a different place where resources for head unit developers is located?
Head units are developed under the aegis of the MFi Program. Quoting this page:
Developing CarPlay systems
Find out how to update your vehicle system to support the latest CarPlay features. Add support for second screens, such as instrument clusters, irregularly shaped displays, and dynamically changing screen sizes. Learn how to support voice activation for Siri. If you’re interested in CarPlay systems, learn more about the MFi Program.
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