Custom airframe file problems

I’m trying to create a new airframe with custom code for the mixers. I found where to add my new mixer class and get it to compile. I created a mixer file and a config file based on existing files and downloaded everything using QGC. Looking on the bootloader.txt file in the sd card shows that my custom mix file doesn’t exist. I tried placing it in etc/mixers and it still says it can’t find it. I’ve tried going through the docs multiple times and I still can’t seem to get everything to work or get placed properly. Can someone please provide a complete example of where to put files, download, etc. It is very confusing how all this goes together. Also a good config example would help. I may be missing a process. I’m building it using "make px4fmu-v3_default since I have a Pixhawk 2 (cube).

Thank you very much for everyones time.

Here is the output from the bootloader.txt file

PX4IO update failed
PX4IO not found
ERROR:[init] Could not load mixer: /fs/microsd/etc/mixers/mytest.main.mix

I see:

PX4IO update failed 
PX4IO not found 

This would hint that your PX4IO fails to update and probably doesn’t run correctly. This would explain that the mixer can’t be loaded.
Can you post the whole output, and maybe show the changes that you have been doing to a branch on your fork to see the changes?

That was the whole output of the bootloader.txt file. It was just those 3 lines repeated 3 times. I was assuming that the update failed and not found messages were caused by the mixer file not being found. Maybe that was a bad assumption.

Ok, can you delete the files on the SD card, then unplug the Pixhawk and press the safety button while powering the Pixhawk again. That should force a PX4IO update.

@smgoza Did you find a solution to this? I am facing a similar problem

Yes the problem was px4io being too big for processor. I believe the make file now tells you of the size problem. If not then in nsh on console the px4io status command will tell you. The other problem I was having was the mixer file being too big. There is a variable in code called something like MIXER_LENGTH that sets the string storage length. Don’t have access to code right now for exact name

Look for this PX4IO_MAX_MIXER_LENGHT. Happened to see it on another thread

Can you give me the file list which needs to be changed for a custom model ?