4-Axis RP5 with Bigtreetech Octopus Pro- How to make axis indipendent

 
Hi all,

I am developing a 4-axis foam cutter using a Bigtreetech Octopus Pro V1.0.1 F429 connected to a Raspberry PI5 via SPI.
I have amended the Config.txt file, the .hal and .ini, and named the axis as X, Y, A and U.

What happens is the following:
1- X and Y axis work fine.
2- If I try to move the A-axis, then both A and U move.
3- If I try to move just the U axis, then nothing happens.

What am I missing?

I have attached the board pin mapping, the Config.txt and my .hal and .ini files, which were modified from those in the remora "ConfigSamples"  directory.

Cheers
Pier