Current state of the code:
- My first Purpletooth board stopped working, stopped responding on the serial port, and I had to get another one.
- It still has the slowness problem in standard AVRCP mode.
- I can switch it to AVRCP "Old" mode, which is pre-AVRCP-1.3 without track metadata, and that makes the slowness problem "mostly" go away.
- But even with "Old" mode there are still problems...
- The Play/Pause buttons don't work, only the next/prev track buttons work.
- FF/REW are nonexistent.
- The headunit starts off stuck in "pause" mode and won't come out of it.
- I can work around it by sending the play command up to the headunit after bootup, and and then the headunit goes into play mode and then it plays.
- But then after that the pause button works... Exactly once and then it gets stuck in pause mode again until I send another Play command up the chain.
- I have coded a somewhat flaky workaround in which my code always sends up the Play command to the the head unit. This tricks the head unit into always thinking it's in "play" mode and then you, the user, can use the pause button if you want. It tries to keep track of what state the player is in (either playing or pausing) and then sends the necessary command to toggle the state. But it doesn't work super reliably.

I've finally found out how to talk to the chip people on the Sierra Wireless forum and I'm getting some response, though they don't have a Honda to test with and are unable to reproduce my problem so far.