See attached pic.
Update: Now fully working!
Getting ~12 fps using just one cog on 80 MHz P123.
But, speed can be dramatically improved (by going to 240+ MHz and using more cogs).
Features background, textured walls and textured floor.
Far away walls now a bit darker.
You can see where I got this idea from here: https://permadi.com/tutorial/raycast/demo/5/
Try it out! Download the attached binary to your P123 and then use the left 2 buttons to turn left or right and the third button from the left to go forward. (Note: the button on the right is the reset button).