FWIW to leave an update about my software work I'm going to put it on ice for now, as cc3dfs on github just commited today, some basic support for CypressUSB Nisetro devices (which is what these DSi's use). Which is very similar to what I had locally in terms of what it's doing over USB. Seems like we won't need to build our own thing. I was able to do some basic testing, and get it to work, so I think i'm going to hold off on just building my own version of something that already seems to work fine. It's behind a flag right now, so a user would still have to compile with extra flags, but seems like they're working on bringing it forward.