[colug-432] hacking embedded linux

[rhornsby at ktzr.net]

Most (all?) smart tvs these days are running some form of linux or another. For the last few years, I've been hooking up RaspberryPis to make the TVs do other things than what the pre-packaged software allows. With the shortage of PIs, and it finally dawning on me that all the hardware to do nearly everything I'm getting the Pi to do is already in the TV, already paid for - right there in front of my face, I've been trying to hack a couple of different TVs I bought specifically for the purpose.

One is a mid-range ($250-ish) Vizio, the other a similarly mid-range Samsung. I've been able to get UART on both of them using a bus pirate. I can see the serial console scrolling by, see it booting up, etc but can't seem to do much else. I was able to interrupt the Vizio a couple of times by getting lucky hitting <some key on the keyboard> and got an unresponsive prompt(?), but that's as far as I've been able to get.

I'm 99% sure I've got the right TX/RX pins on the Vizio (there are only three connected on the board - TX, RX, and GND) and ~95% sure I've got it right on the Samsung as well.

I have a few goals:

• Disable all the phone-home telemetry crap these things do. It's ridiculous. (ie My PiHole often has a warning that the Roku's DNS is being throttled because I block the upstream Roku logging/telemetry servers, and the Roku apparently freaks out.)
• Leverage existing UI for things like setting up the TV's WiFi, with the assumption that at least later there won't be a keyboard/mouse available.
• More importantly than those though - make the TV do something I want it to do, like immediately load and display a web page after starting up - sort of an unattended kiosk thing.

There are some displays, mostly by NEC, that accept a Pi CM4 board internally but they're stupid expensive compared to a standard TV, and as noted above, all the hardware needed is already in these "smart" TVs.

Anyone tried to hack stuff they own? Any suggestions? If it helps, I have a bench oscilloscope but tbh don't completely understand how to use it properly, except for sometimes I can get it to show me sort of "oh something is happening"

thanks!
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