count_on and _off - 8 bits, 256x10ns = 2560ns.

count_on+count_off = 255 = 2560ns for 1 cycle.

change_width is 7 bits, 128 full scale.

so the duty cycle changes every 128*2560ns = 327.68us.

the duty cycle increases until we get to full, which is 254,
and then decreases until it gets back to 1.

that takes another 254*2 counts = 508

so one cycle should be 327.68us * 508 = 166ms

so it 10ns * bits_on_off (255) * 2 * bits_change(127) * bits_on_off(255)

=10ns x 255 * 128 * 255 * 2 = 166ms