Tuning Geckos

Hello again all.

I'm getting to the point where I'll be needing to tune my geckos.
I've got my o-scope all set and ready, however, I don't own a
function generator so I can't really generate the step pulses I need
other than using a parallel port.

The gecko docs say to ramp up a square wave of pulses and then
reverse the direction pin... then watch the scope.

is there a good way to do this in emc? I was thinking I could set
up the accelleration profile to a high extreme so that the change in
direction would be almost imediate. I'd jog in one direction, then
jog in the opposite direction (or a qick bit of G-code to move back
and forth)

If not, I'll throw together a classic 555 timer to make some pulese
for me. Does anyone know what frequency range I should be looking
for when tuning?

As always, thanks.
Jake