When i've saw it first time i've immediately thought it's possible to integrate MiSTer inside.
Thanks to developers who don't assign very specific place for Raspberry Pi and give a lot of freedom to integrate something else.
So it turned out embedding of MiSTer wasn't easy, it was super easy! Space inside is deep enough to accommodate even standard SDRAM vertical module. Originally i was thinking to add some retention using RPi holes, but SDRAM module has height just exact to case height inside, so it keeps MiSTer perfectly. Additionally cables keep the board in place.
The only challenging thing was to find a short thin and slim MicroHDMI - HDMI cable. I've found 50mm cable. 20mm or 30mm should be even better.
I've soldered MicroUSB -> USB-A cable to get RasPad 3 USB hub working.
Also soldered Type-C -> barrel cable to power the MiSTer.
MicroSD card breakout cable is unfortunately too short for MiSTer. You can try to find a longer ribbon cable. I've decided to go a simpler for me method - i've soldered the cable
But even without extension cable you can use SD card directly in MiSTer. It's seldom need to be extracted. The only breakout cable was used without any change is Ethernet
That's all.
Here is the result: 1) USB hub in RasPad 3 is USB 3.0 and it works fine in USB 2.0 mode (de10-nano has USB 2.0 only).
2) Battery works fine, but i can't tell how long it lasts yet. Charging circuit is classic slow charger, so it needs quite some time to charge.
3) RPi4 has two HDMI outputs, and RasPad3 uses this feature to use LCD panel and external HDMI at the same time. MiSTer has only single HDMI, so external HDMI is not working. With some additional work it's possible to integrate some small HDMI splitter and get external HDMI working too. But i suggest to have just additional MiSTer for RasPad3 for mobile-only use.
4) Internal speakers work fine from HDMI source. Audio is muffled though. You need to lift the RasPad 3 a little to get a better audio.
5) RasPad 3 board works quite independently, so you get icons for charging and discharging as overlay on top of MiSTer video. There are 3 LEDs on the side to show the current charge level.
6) Original fan is quite noisy even in slow mode. I've used my favourite quiet ADDA fan without heatsink. That should be enough as originally FPGA is supposed to work in up to 100 degree. Effect of this cooling isn't so good, but enough i think.
The only thing i couldn't make work is touchscreen. It's not that touchscreen is really useful for MiSTer, but would be good to make it working. I had plan to simulate a light gun for supported cores. That would be fun and a whole new experience.
Unfortunately de10-nano simply doesn't see touchscreen at all. Even lsusb doesn't show any unknown USB device. Probably it's a classic de10-nano USB host issue when some devices simply don't work.
There is also a chance that touchscreen somehow depends on HDMI and may be needs some additional initialization. Actually i've tried to connect USB hub to my Windows PC and it also doesn't see the touchscreen. I've tried RPi4 - it sees the touchscreen, so i've confirmed it works in original RPi4 config.
So probably i'm missing something here.
But anyway RasPad3 adoption already works fine. You get a portable MiSTer without any difficulties in embedding process.
