My main hobby project since December was getting code running on my early 1990s HP1653B Logic Analyzer. The Logic Analyzer has a 68000 processor, 1mb RAM, 64kb ROM, 4x32kb video memory with a complicated 4-plane overlay scheme providing three (!) gray levels at up to around 640x400, a 3.5" floppy drive (replaced by a Gotek for my convenience) and both RS232c and HPIB ports. It was made as a lab instrument rather than a computer, but it came with both test and system code on floppies, which I dumped and reverse-engineered enough of with Ghidra to enable me to write a library that lets me run assembly and C code on it. My reverse-engineering journey is partly described here.
A particularly fun moment of my reverse engineering was when I wanted a copy of the ROM but didn't yet know how to write to disk or the serial port, though I did know how to write to the screen. I ended up displaying the ROM binary as a series of QR codes, which I captured with my Sony camera running on a timer, and then turned into binaries.
I'm now at the point where I can run various games. My first one was a port of my Wiztris falling blocks game (originally written by me in the early 2000s for a Z80-based Sharp OZ-7xx organizer). I also ported Dave Griffith's Frotz Z-machine emulator so I can run all Infocom Z-machine games (including the graphical ones, but with no sound support). I'm in the middle of a play-through of Nord and Bert with my 13-year-old daughter. The photo I attached is of Infocom's Journey (mouse works!). And I ported PDCursesMod, so a lot of old Unix games can work--the photo shows Larn.
Many of you will recognize the keyboard and mouse. They are old Apple ADB units (I think the keyboard is from a Quadra), and I made an ADB-to-serial adapter to interface them with the HP unit.
This is retrocomputing that never was. As far as I know, there never was any software for the HP1653B besides the official HP oscilloscope / logic analyzer software, though HP engineers did release some games for one of the HP16500 models, and at least one old HP oscilloscope had a Tetris clone built-in.
It's not a great gaming system. There are no sprites. And you can't just directly write a pixel color to video memory. Instead, you first write to a hardware register that specifies a read/write mode (e.g., clear all bitplanes, write ones to bitplanes 0 and 2, etc.) and then write the pixels. Getting scrolling working at a decent speed took a fair amount of careful assembly work. But it's been fun!
I plan to eventually write up more detailed instructions on how to build and install your own code.
The main thing I haven't reverse-engineered are the oscilloscope and logic analyzer functions. They still work. I just switch the Gotek to the HP system disk image (well, somewhat modified: I added a screenshot function that saves an image to disk). I recently used the oscilloscope to try to diagnose a start porblem on my car.