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diff --git a/docs/4a-framework/README.md b/docs/4a-framework/README.md new file mode 100644 index 0000000..90de65b --- /dev/null +++ b/docs/4a-framework/README.md @@ -0,0 +1,42 @@ +# AGL Advanced Audio Architecture (4a) + +## Abstract + +4a is an audio framework made to handle automotive use cases like stream +priority and interruptions. It does **not** deal with the audio by itself but +rather with the policies and signaling around it. This means that 4a must be +used in conjunction with an other API that is in charge of the audio stuff, +like **alsa** or **pulseaudio**. + +## Architecture + +### Global architecture + + + +This diagram shows the global architecture that any application playing audio +should follow. As a developer, when you want to play audio, you rely on APIs +such as alsa, pulseaudio or higher level API(s). To play audio you usually have +some kind of device URI that you have to open in order to write audio data to +it. + +4a does **not** change anything about that. You still have to do all of this. 4a +provides permissions, signals and policies. This means that all compliant +applications have to ask 4a for a 'role' when they want to play audio. If 4a +grants them the permission, it returns a device URI that applications have to +open. + +Nothing prevent an application to directly open a device, but in this case no +policies can be applied and access permissions are handled by system policies. + +### 4a Architecture + + + +Even if applications only deal with the high level API, 4a is made of multiple +components that rely on each other. + +The high level API uses the hal-manager to list enabled HALs then it uses +directly those HALs. + +HALs rely directly on drivers and/or softmixer. |