Smoking Gun for sure
Finally the debug effort is finished. I traced the no boot issue to a bug in ProDOS. This error exists in both ProDOS version 1.2 and 1.9. But I see it has been fixed in version 2.0.1. I just need to do a work around in my ROM code to make sure I do not trigger this bug. Then I can continue firmware development of the Serial Virtual Drive. When I get this working, the floppy is the next task. I have done some testing on the floppy and I believe it is working. But the final test will be to load a DOS 3.3 image into the RAM and try to boot from the floppy. If it works, then it is party time. The only thing left after that is to build the Joystick interface and get it working. This should be pretty straight forward.
I just noticed I have been working on this ProDOS error since June 8. So I have been working on this for approximately 50 days.