Doug,
Get well first!
Keep your JL1 in the box for now and use BluePill, the board, not the other thing.
In my firmware thread I’m trying to use factory boot loader. There is some primitive scrambling. Maybe you can see some pattern?
It is not a problem to compile with start offset, and as I understand now not a problem to figure out that offset, but that scrambling makes it so far not practical.
It would be nice to use factory boot loader to update firmware. If you use STLink - you will loose that boot loader.
I have no doubt in your success of getting serial prompt from Blue Pill quickly. It took me 10 minutes. Edit CPU_MAP header file and you are done.
Took couple days to find my starting point source to compile cleanly, just a leg work. There are literally hundreds of forked sources and most are abandoned.
Fun part was to move spindle/PWM signal to new pin, as it was hardware tied, normally defined with HALCoGen (Cube MX). Every time I touch Halcogen - it breaks. So I end up not redoing HAL but adding/overriding relevant part of HAL at the end of init.
Lets see how you can solve it! As professional firmware developer - you have advantage.
To help you get started - here is my pin map for JL1, saves you a few hours of signal mapping. It is very possibly not complete. I suspect there might be boot pin for ESP, but I yank module out early and had no real reason to check every connection to ESP. Maybe handy to re-flash it with ESP3D interface.
JL1 STM32 pin map.txt (370 Bytes)
I have started to prune the code/commenting out every unused pin and did a few, but some are still there. Does not appear to interfere with anything.
Waiting for your updates. Maybe better to discuss development in JL1 firmware thread.