I did this project to keep myself occupied while recovering from some surgery in 2015, for which I would have limited mobility for about a month. I didn't think I'd be up to doing bench work, so I used some existing PCBs to allow me to focus on the firmware, which I could do lying down (both literally and figuratively). I used a UBW32 (from Schmalzhaus) as a CPU 'breakout board' and also a UBW32-MCC (from Dontronics) to provide the VGA, PS/2 keyboard, SD card, and power connectors.
"If I have seen farther than others, it is because I have stood on the shoulders of giants." -- Newt.
Props to Geoff Graham, who allowed me to pilfer his Maximite code for the video and keyboard 'drivers'. And also indirectly to Lucio Di Jasio, for describing the clever 'SPI and DMA as a video generator' technique, which was used in Geoff's project (and by extension, mine). I am very jealous that I can't claim to have invented that myself! Brilliant!
Props also to Tim Mann, a developer of software for the TRS-80 (actual) back in the day, and also creator of the 'xtrs' emulator for unixian systems. I used the Z80 CPU emulation code (which I modified a bit for my purposes). (It, in turn, is derived from another source which I cannot name, or else I'd cite it as well. Clarendon Hill? Either way, the license seems functionally public domain.)
Props also to Matthew Reed, author of TRS32, an excellent (albeit non-open-source) emulator for Win32 systems. I use it sometimes for comparison, and also the TRSTools are quite useful for extracting files from floppy images.
Props also to all those others who helped kept the memory of the TRS-80 alive; otherwise I would have had scratch to work with when starting this out.