It has two microcontrollers on it. One is on the carrier board, which I assume interfaces to the Apple 2 bus. The other one is on the daughterboard, which also has the HDMI port on it, which I assume is some kind of all-in-one handyboard type unit that he just plugs into the carrier board. My assumption is that the carrier uC sends video state info to the daughterboard during vblank or something.
There's a 9-pin header on the daughterboard that I assume is USB, for re-flashing the daughterboard firmware. The daughterboard has both an SD card slot and a USB port, so I assume that its firmware can be updated as well.
I haven't messed with it much yet, but it takes about 6 seconds for the card to initialize. This is slower than the system boots with a floppy emu, although it's easy enough to hit control-OA-reset once the card comes up.
Since I already have an additional 5v 3a power supply in my system to power the Pi3b+/Rock64 boards (and future microcontroller projects), I am hoping that I can power the video card off of that instead of off the //e bus, so that it just stays on all the time and doesn't need time to initialize when I power up the //e PSU. I don't see any headers or jumpers for doing that, though, so I assume that my only option (aside from cutting the 5v pin on the mobo side of the connector, which I certainly will not do) is to peel the 5v pad off the card and solder a jumper wire on. I am loathe to do that to a $135 card, so I'll probably use it as-is for a while just to have a good burn-in period to uncover any issues before I start cutting on it.
The included documentation is rather sparse (one page, good enough to get going). There's a link to the full manual with the included quickstart doc, but following it leads to an "Under Construction" page.
All in all, I am very happy with the product. When I think about what it takes to interface a uC to the //e bus without any glue logic (doing it all in software), it blows my mind. The creators of this product would appear to have serious skills and really know what they are doing.
Now if we had a similar "smart carrier" for the A2Pi stuff, instead of doing it via serial with UARTs that are basically NLA..... Well, that would be really sweet.
Edited by Lee Adamson, Tue Jan 29, 2019 6:57 PM.