[MTCD  Android Head Units Q&A] forbiddenera:
Hi,

I am also very interested in using USB Audio on a PX5.

I have an EONON GA7150A 32GB BMW unit.

MCU is "MTCD_WWW_V2.54b_2", Build is "px5-userdebug 6.0.1 MXC89l user.hct.20170617.171922 test-keys"

I run a car audio / performance / engineering company. We're doing a SQ install on a 04 BMW M3 with all Audison Prima gear going to an Audison Bit 8.9 amp/processor.

I got a Behringer UCA-222 hoping to use it - plugging it into my tablet (Samsung Tab S 8.4") - it works perfectly without any configuration, so I had hoped it'd work with the Android HU as well.

Plugging it into the Android HU - it DOES work - I can play audio from any apps (YouTube, Google Voice Search both output to the USB device) - I have installed SoundAbout Pro to try and re-route all audio to the USB DAC but it doesn't work for everything.

My issues are:

- The FM radio plays through the internal pre-amp/amplifier.

- The volume control (whether through the touchscreen on the menu, or using the hardware knob) does not affect the USB device - there is no way to change it's volume from the head unit this far.

I'm ready/willing to flash/hack this unit as best I can, can't brick it as it belongs to a client (fingers crossed) but I definitely want to use the USB DAC full-time.

If I could find a way to loop the RCA inputs to the optical output on the UCA222 (maybe a custom app) that would be enough to route the radio output through the optical but that's definitely not ideal.

There has to be other people wanting/needing to do this! These units DACs leave a lot to be desired (I'm being nice) and there's a huge selection of great USB DACs.. Heck, in my configuration I won't even be using the DAC in the Behringer - it'll be all digital until it hits the Audison processor/amp with it's internal DAC feeding it's internal amp and a pre-amp that outputs to the separate sub-woofer amplifier (AP1D).

I have the deck setup on my desk right now hooked to a power supply and booted, on WiFi and ready for hacking. What can we do?

From what I've read the MCU controls all the hardware buttons - though I'm not sure it'll be required to mess with it..?

How does Android see the internal audio chip? I know the MCU communicates with it over SDIO, does android as well? I guess no as I read another thread that has a hack/app allowing more control over the audio chip by interfacing one the SoCs GPIO/SDIOs to the chip.

So, how does the radio app work then? Does it just send a signal telling the radio chip to route its audio to the audio chip? Or does Android actually see some sort of audio device for the radio? If it just tells the audio chip which "source" to use and the radio chip outputs directly to it, I'm not sure there's going to be a way to get radio over digital without a converter box to convert that analog output to digital..

All other Android outputs shouldn't be a problem, from what I can tell everything else is already playing over USB for me.. except the radio and volume control.. even the "beeps" you hear when adjusting the volume come over the internal audio device not USB..but Google Voice Search and YouTube work over USB fine..

---------- Post added at 03:05 AM ---------- Previous post was at 03:04 AM ----------

I find it odd that your seeing pops/clicks.. I have had no issues and fully stable audio from the apps it does work from.