[Connected Car] Prostheta:
I've been tinkering with a USB C-based semi-permanent tablet install into the console of my Chrysler 300C using a Samsung Galaxy Tab A 10,1. The key difference is the "semi-permanent" part, as the build needs to be self-sufficient running in place as opposed to being the removeable sort. This implications of how this affects power and USB hub power enumeration is key I think.

So, the install is as by 1.jpg attached. Fairly straightforward and not unlike most installs done since forever. A spare console was modified with a bezel fabricated around the tablet's screen size shown in IMG_20200504_184515.jpg. As you can see....the intention is to get a "factory installed" sort of look.

The problems I'm experiencing seem twofold....but both may be solved by the same answer.

Firstly, when powering the car down and accessory power is cut, the negotiated power arrangement with the hub is as per 2.jpg; the tablet takes over the role of being power provider to the hub. Ampere shows a power drain of about 1,5A which drains the tablet's internal battery in an afternoon. Powering down the tablet is one solution, but hardly elegant as ideally it should sit in a deep sleep condition and wake upon receiving power, not providing it. This would seem like a root-level change that I am not sure how to do, or if anybody else really has been working on. Any comment is welcome, as the Internet doesn't seem to be forthcoming with answers, but plenty of questions.

Secondly, when accessory power is active with the engine running (key in ON position) the tablet doesn't always seem to mount the SSD. However with the key turned to ACC or ON, it does. This is not always the case however, and with a bit of luck (I haven't found good rhyme or reason here yet through testing) the SSD does mount whilst the engine is running. I haven't an easy way to test this, however I believe that this applies to the DAC as well. A clue here might be in the status of USB charging; the tablet doesn't charge when the devices are mounted. When they are not mounted, the status is either "USB Charging" or "Cable Charging". Either of these modes are providing insufficient power to keep the tablet's battery receiving more power than the tablet consumes. Problematic and might represent a third point....not sure.

The solutions, or at least the tests that I have involve throwing money and components at the problems which isn't the logical approach. Recognising the issue better needs to be done first. The difference in accessory power between the key positions ACC/ON and START seems both odd and unlikely. The charger port can work 11v-24v so is well within the specified range of supply voltages. In ACC/ON the battery provides around 12VDC which is as expected. When in START, the voltage rises to 13,8VDC which should also be fine. I'm wondering if the momentary switch between voltages or loss of voltage between these states is kicking either the charger or USB hub into renegotiating supply levels and arrangements. This is another difficult to test scenario. The most I think that can be done is to manually plug in the hub to charger port whilst the engine is running to get a "clean and new" negotiation. If this is in fact the issue (or "an") issue then what's the solution? A capacitor to smooth this transition? A better/different charger port?

I've considered whether a power bank might provide some additional solidity between the charger port and the hub, however I think it would introduce additional alterations to behaviour that aren't desirable. For one, the tablet system would consider itself to be "always on" whilst powered by the power bank. Currently, AutoMate switches the screen on and off based on USB supply to the tablet and kills/suspends processes accordingly. The most a powerbank might do is to clean up any sort of power and mounting negotiation glitches that occur, at least in theory. Again, throwing ideas and seeing what sticks isn't the best solution.

Having second opinions and bouncing ideas around would be useful. Anything anybody can add, or questions that can illustrate tests and further information would be fantastic. I know that I'm not the only person in this boat!