Oh, I see where i went wrong.
I modified the makefile for linux (retrofw is linux after all), and built it that way.
I tinkered around with the code and worked out how to change the resolution by fiddling with the code and doing a desktop linux build of powder, got it down to 320x240 (native for the LDK i'm working with as far as i've read)
it runs, but it still looks weird. I also realized doing a standard linux build its expecting keyboard and mouse instead of just the few keyboard keys the buttons register as, so i would have to work out an input routine like you have already done.
I'm assuming you modified an existing dingoo port to work on the rs97.
i'll have to try to get yours up and running.
I'm new to porting things, I've took a few x86 linux games and tweaked them to get them running on the raspberry pi (powder, cataclysm:dda, brogue) but never anything this deep down the rabbit hole.
by the way, I never found any one mention the developer backdoor on the retrofw firmware, so i figured i'd mention it here:
no clue if it works on windows/osx due to drivers, but if you plug a usb cable in, boot to the Ui and press b to not do file transfer but charge only... On a linux desktop about 30 seconds later a usb ethernet adapter shows up and automatically assigns an ip address to your pc of 169.254.1.2 (the rs97 device itself is 169.254.1.1)
port scanning it i found that ftp and telnet are open login for telnet appears to be root, no password. ftp works anonymous, very handy for remote testing/debugging.
I'm assuming it work just as well on a linux vm as long as you handed the usb port off to the VM.
I'm currently in the process of getting buildroot back up and running with sdl2, going to see if i can get blake stone
up and running, but i'll have to try your build and see exactly whats different from what i was trying to do.
edit- forgot to ask/add
the specs for the cpu/SOC should support USB OTG, i'm not sure if the hardware exists to enable it, but just curious if anyone knows if that is something that could be made use of? plugging in a keyboard, second gamepad, or even something like a wifi adapter via USB OTG would be cool.
had to modify /rs97_dev/powder-rs97/port/dingoo/hamfake.cpp:147 changed SDL_TRIPLEBUF (errored during build as if it were nonexistant) to SDL_DOUBLEBUF to get it to build, maybe i need to update buildroot?
running a quick feature test, i noticed a couple tilesets cause the screen to go blank (akoi meexx 12, ibson the gray), i'm assuming they're different size tiles compared to the others.
nice work @bopbopbop