This signal on the DevKit is not routed externally, so it cannot be tested.
I have test the below period/duty_cycle values:
period=10000, duty_cycle=5000, Yes
period=100000, duty_cycle=50000, Yes
period=1000000, duty_cycle=500000, Yes
period=10000000, duty_cycle=5000000, No
I think it should be same as this post, and I know what to do now.
Many Thanks!