Not CPU design, but does involve a simple VM, have you checked out 2019? About half (1/3rd?) of the challenges involve a VM for "intcode". First few challenges get it up and running, then concurrency is added, and then challenges are presented inside it.

Really enjoyed that one. I do it in Excel, and moving things around between registers actually maps really well to a spreadsheet.

Thanks, I'll check it out. Definitely close to my definition of fun :D

I also cannot tolerate hard problems so probably will stop around the same number.

If you enjoy that, the same guy made Synacor Challenge: http://challenge.synacor.com

Similar basic problem as the intcode VM but less need to dive into concurrency.

Thanks! This is really cool~

One of my dreams is to consume small pieces of challenges of some topic, one sightly more involved than the previous, then viola! At the end I get to learn say 50% of a CS course.

Books are good but they don't force me to write code. I'm a bad learner :D