It just implements LEDChaser from the LiteX LED core demo, where io_in[3:7] is duty cycle
Add LEDs on the outputs in a straight line -- or probe all signals on a scope and check that you get a 'moving' train of pulses.
| # | Input | Output |
|---|---|---|
| 0 | clock | led a |
| 1 | reset | led b |
| 2 | pwm_width 0 | led c |
| 3 | pwm_width 1 | led d |
| 4 | pwm_width 2 | led e |
| 5 | pwm_width 3 | led f |
| 6 | pwm_width 4 | led g |
| 7 | pwm_width 5 | led h |