First some good news :
pyra booting pyraos with a TILER enabled kernel.
It still needs a very ugly hack to keep the display on for more than 10 seconds, but at least the basics work. (no display until it loads the kernel modules, which is why you don't see anything the first 19 seconds, and the annoying flashing leds are turned off by my led-config, the one "failed" message you see is just the sgx driver modules failing to load)
It's still quite a struggle to boot the thing though, but once it does, its fairly stable when both usb power and the battery are used. USB power alone tends to drop out when the load gets higher. Taking out the battery while on USB power also seems to cause a drop in brightness of the leds.
Booting usually gets stuck on the u-boot "Starting kernel ..." message. Although sometimes it doesn't even get beyond the first two lines : "U-Boot SPL 2015.10-00064-g3a56b36-dirty (Apr 07 2016 - 22:35:27) OMAP5432 ES2.0 "
It seems it gets easier to boot the longer you try, like something needs charging/warming up first :)
I did take apart the entire thing, and after that booting does seem to have become slightly more reliable. Maybe it has something to do with that cpu board not beeing mounted properly in the second socket. At the angle it sits it's a miracle it works at all. Although I also took out the stuck shoulderbuttons. (not sure if they were pushing down on the buttons, but they didn't move anyway)
Another thing I noticed was a high pitched whine when plugging in usb devices.
When using the letux makesd created image, there's a 3 minute delay halfway through booting, right after "[ 15.161997] wlcore: loaded" After the delay, it continues booting without problems. I didn't really investigate what caused it, it doesn't happen when using the pyraos image (probably because that uses the much more parallel systemd) Also, devmem2 seems to be missing from the image, the package is there, but the executable isn't found, which causes some issues with the lcd script (which doesn't seem to be needed on my pyra anyway, since the display just works when using omap5-letux-cortex15-v5.1+pyra-v5.1.dtb)