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BEMF goes the wrong way

Associate II


I am struggling with the appearance of my BEMF in my 6 step control.

The picture shows one of the phases. And according to all the documentation I've seen ( and I have read a lot ) my BEMF goes the wrong way. The BEMF looks like outstanding ears but it should look like hanging dog ears ( hope that made sense).

I hardware is homemade running a STM32G474. 

 The PWM is unipolar i.e the lower mosfet is on, during the step, and the PWM is done with the upper mosfet. 

At this stage I am bit-banging ( very temporary of course) the PWM so that I have 100% control of the ON/OFF-state of all 6 mosfets. 

I think my plan is to detect BEMF during upper mosfet On-time compared with virtual GND.

Any thoughts why my BEMF goes the wrong way is appreciated.