Impossible to back to AA after exit

[EgorMaryasov]

After exiting AA(car icon), it is impossible to launch AA again on a wired device. You need to disconnect and reconnect the wire.

[andreknieriem]

That is a problem of android itself. @andrecuellar or am I wrong?

[EgorMaryasov]

Headunit Reloaded 7.0.4 does not have this issue. Exiting via the car icon does not work there. But if you completely exit AA by swiping back a few times(gesture control), then you can return to AA by selecting the USB device. I have tried Headunit reloaded 7.2.3 also, and it has the same issue as Headunit Revived.

[andrecuellar]

Hey @EgorMaryasov

@andreknieriem yeah, you're right, this is mostly an Android thing. When you exit AA the app closes the USB file descriptor, and the phone drops out of accessory mode. Android's USB Accessory API doesn't let you reopen that connection without the device going through enumeration again (unplug/replug or reboot). That explains why HR 7.0.4 blocks the car icon exit entirely, they're just avoiding the problem. And the fact that HR 7.2.3 has the same behavior as us confirms it's a platform limitation.

There might be room to try a softer approach (release and reclaim the USB interface instead of closing it entirely) but that's tricky and behavior varies across devices. Something worth looking into eventually.

For now @EgorMaryasov check Settings > Automation and enable "Auto start on USB" + "Reopen on reconnection". That way if the phone comes back to accessory mode on its own, the app will pick it up without you having to manually reconnect.

[andreknieriem]

Thanks @andrecuellar . Close this for now ;)

[EgorMaryasov]

I have tried "Auto start on USB" + "Reopen on reconnection". It does not work.
Original AA let me return to car interface(car icon) and come back to AA(AA icon) without any issues.
Headunit reloaded 7.0.4 let me come back to AA if i completely exit AA by swiping back a few times.
Headunit Revived does not allow me to return to AA, neither if I exited using the car icon, nor if I exited using swipes.
BTW, car icon does not work in Headunit reloaded 7.2.3 , but it have same issue with Headunit Revived. It is imposible to reconnect to AA after exit with swipes.

[andrecuellar]

@EgorMaryasov thanks for the extra details, that helps clarify things.

The reason HR 7.0.4 lets you go back to AA after swiping out is because it doesn't fully close the USB connection when you exit. It just closes the projection screen but keeps the USB transport alive underneath. So when you "select the USB device" again, it simply reopens the projection on the existing connection. That's also why the car icon is blocked in 7.0.4, because that one would trigger a real protocol disconnect (ByeByeRequest) that they can't recover from.

HR 7.2.3 has the same problem as us because they likely changed to doing a full disconnect on exit, same as we do.

In HUR, both the car icon and the back gesture call the same disconnect flow: ByeByeRequest is sent to the phone, then the USB file descriptor is closed. Once that file descriptor is closed, Android drops the phone out of accessory mode and there's no way to reopen it without physical reconnection. That's an Android USB Accessory API limitation.

Changing this would mean rearchitecting how exit works, separating "leave the projection screen" from "disconnect the USB transport". That's a significant change that could introduce instability in the connection lifecycle and affect all users, not just this scenario. We can't offer a fix for this right now.

For wired connections, the recommended workflow is to stay in the projection screen while driving and only disconnect when you actually want to end the session.

[EgorMaryasov]

I use Carlinkit Ambient Android box(https://www.carlinkit.com/ambient). It has no battery. If i accidentally exit through the car icon or by swiping, i need to reconnect the cable and then wait for Carlinkit Ambient to fully load. This is inconvenient. Please consider adding an option, the activation of which would reproduce the behavior of Headunit Reloaded 7.0.4.

[andrecuellar]

@EgorMaryasov I understand the frustration, but I don't think this is something we should change in the app. Let me explain why.

Headunit Reloaded stopped doing it too. You mentioned that HR 7.0.4 worked but HR 7.2.3 doesn't. That's not a coincidence. They moved to a full disconnect on exit, same as us. Keeping the USB transport alive while the AA session is closed likely caused them problems: zombie connections, resource leaks, inconsistent states when the phone side times out or moves on. If it was a good approach, they would have kept it. The fact that they didn't tells us something.

Adding this would be a regression risk for everyone else. Right now the disconnect flow is clean and predictable: exit AA, send ByeByeRequest, close transport, release resources. Splitting "exit the projection screen" from "disconnect the transport" means rewriting the core connection lifecycle. That touches every user, not just your scenario. We'd be adding complexity and potential instability to solve a problem that only affects a specific device. The vast majority of users have no issues with the current reconnection behavior.

It works fine on other adapters. I personally use a wireless AA adapter (USB dongle to head unit, same concept as your Carlinkit) and reconnection works flawlessly in every scenario: exiting AA, disconnecting, coming back after 2 minutes, coming back after 8 hours. The adapter handles the ByeByeRequest, recovers, and reconnects without any issues. This tells me the problem is not in how HUR disconnects, but in how the Carlinkit Ambient handles the reconnection on its side.

Changing the USB connection lifecycle without being able to properly test it on the affected hardware would be irresponsible, we'd be merging changes blind and potentially breaking things for users who currently have zero issues.

The disconnect behavior in HUR follows the Android Auto protocol correctly. The Carlinkit Ambient firmware should be able to handle a standard ByeByeRequest and re-enumerate, just like other adapters do. I'd suggest reaching out to Carlinkit support or checking if there's a firmware update for the Ambient that improves reconnection handling. It could also be worth checking if the issue is specific to your phone model or Android version.

I wouldn't add this feature because the risk of breaking things for the majority of users who have no problems far outweighs the benefit for one specific adapter that doesn't handle reconnection well.

[andrecuellar]

Personally, I won't do anything about this issue; I have a feeling that adding something like this to the current logic will only cause more problems.

[andreknieriem]

The only other solution is just to keep the connection and everything alive on Exit and just Switch back to the Main Screen. But if you are playing music etc it keeps playing. I really don't why to click Exit if you don't want to exit. Makes no sense to me.

[EgorMaryasov]

"I really don't why to click Exit if you don't want to exit. "
To turn on seat heater for example. Or to change air condition temperature.
A lot of Chinese cars have no physical buttons for it.

"This tells me the problem is not in how HUR disconnects, but in how the Carlinkit Ambient handles the reconnection on its side."
Samsung S25 Ultra - same issue, it is imposible reinter to Headunit Revived AA after exit with car icon.

[andrecuellar]

@EgorMaryasov A few months ago I added an improvement so that when minimizing the application using the home button, it can return to Android Auto projection when reopening it. You don't need to click the exit button, which is literally for exit.