Re: freqmod - step pulse timing

[Fred Proctor <proctor-at-cme.nist.gov>]

Joel,

As you discovered the EMC motion controller assumes a step on the rising
edge of the pulse. Also, if the direction bit changes, the step bit
change is deferred for one cycle so they don't change at the same time.

The choice of a step on the rising or falling edge of the output pulse
should be .ini-file-configurable, but it's not. I will change this so
it's configurable on a per-axis basis. Also, the clocking is inhibited
when the motion controller is computing zero speed, which may happen in
mid-pulse. So, you may see your output left high half the time when
moves are over. I will change this so that the cycle always completes. 

The output should be a 50% duty cycle, to within one task cycle time,
e.g., you'll either have:

1111000011110000... (4 task periods up, 4 down, 4 up, 4 down, effective
period 8 X task cycle time)

or

11100001110000... (3 up, 4 down, 3 up, 4 down, effective period 7 X task
cycle time)

but never

110000110000... (2 up, 4 down, 2 up, 4 down, effective period 6 X task
cycle time)

instead, it would be

111000111000... (3 up, 3 down, 3 up, 3 down, effective period 6 X task
cycle time)

--Fred