I'm just starting to play with this product
https://www.coridiumcorp.com/SuperPRO.php an ARM based processor. Basic, C and "I believe" inline assembly is available.
I'm having interfacing issues which I'll hopefully work out. I just ordered a bunch of headers, so I can't try out my first "Hello World" program for an serial LCD display. Input will likely be a quadrature encoder so that could be fun. For now, it has a switch and is bicolor. Might add capacitive sensing as well. Not sure.
The other part of my plan is to use two 16 I2C IO devices, 1 with interrupts enabled. The system is 3.3 and what I have to interface to is 5V, so that's the fun part. My platform has an 8 port device which have Isolated modules such as AC IN, DC IN, relay out, buzzer
Furthermore, I want to add the ability to interface the I2C to an isolated I2C device of any choosing power supply from 1.8 to 5V.
So, that will be my development platform to start.
Look what they pack into that thing:
https://www.electro-tech-online.com/custompdfs/2012/08/DS175x.pdf and
https://www.electro-tech-online.com/custompdfs/2012/08/UM175x.pdf
ARM has an interesting architecture.
I go back to the PDP-8, PDP-11, 6800 and 1802 assembly