Optical encoders with DC motors

That is fantastic tommylight! I set up L298N through stepconf as PWM. And it runs. I can control DC motor movement through Spindle STOP button. CW and CCW also works. However, I can only turn dc motor ON or OFF, and then it spins on its own. I would love to be able to control it through "+" and "-" in continuous mode using mouse. If it could spin while I keep pressing "+" or "-" with mouse - it would be perfect.

Does pressing + and - near the spindle button do anything ?

It increases and decreases the speed. If I choose 0 Hz in config, then + or - starts the dc motor CW or CCW depending which one I press. But still, DC motor spins continuously once I press + or -.

That is exactly how it should work.
If you want to do some more testing, try running some gcode with something like this in it: That will run the motor CW for 5 seconds at 100 RPM then run CCW for 10 seconds at 200RPM, then stop.