freqmod - step pulse timing

["Joel Jacobs" <jj-at-netexp.net>]

Could someone tell me please, does EMC expect the stepper controller to step
on the rising edge or falling edge of the step pulse?  Is Direction valid
for a complete +/- or -/+ step pulse cycle?  What is the minimum step pulse
width?  How long after a step can direction be assumed to be valid?

Reason I ask - My controller seems to miss a step sometimes.  I have my
controller set to half step.  When it powers up, it is on a full step.  I
run EMC and at axis 0.0000 it is on a full step.  I run some of the included
.ngc files and the motor seems to run ok except sometimes I sense a jerk -
usually at slow speeds, and when I return the axis to 0.0000 it stops on a
half step (no backlash programmed in).  It should stop exactly where it
started on a full step.  Note - it's the controller that misses a step not
the motor.

My controller uses a micro to decode step and direction.  It uses an
interrupt on the step signal pin.  I have it set to interrupt on the rising
edge but I could change that easy enough.  After it gets a step interrupt,
it takes maybe 1 or 2us max to save context and get to the interrupt routine
where it checks the direction input and decide which way to step.

Thanks for any help!

Joel