DISTRACTIONS WITH VISITORS HOWEVER STILL STUCK
I am finally able to put some time back into the effort to restore a U-boot that brings up my Linux image on the DE10-Nano board. I have been unsuccessful recreating whatever I discovered or did last time that produced a working version. Sadly, after some progress testing the design, I had to make changes that would require an updated U-boot and preloader.
This is because it is the U-boot software that implements the pin multiplexing settings, starts up the DDR RAM and does other initialization such as the F2SDRAM bridge before Linux can begin booting. With changes to the chip configuration, the U-Boot files had to be updated.
I did figure out something that regained the booting when I last built and installed U-boot, so somehow I will find it again. Alas I didn't write down what I discovered nor document all the permutations and adjustments I had tried during that journey, so I have only hazy memories to guide me this time. If you can all be patient, I will be relentless until I get this fired up again and can continue perfecting the design of the Virtual 2315 Cartridge Facility.