ErikZalm/Marlin — pull request #160 by JTrantow (2012-05-04 20:08:49+00:00)
Title: Update Marlin/stepper.cpp

The original Marlin firmware sends out a step pulse by toggling the _STEP_PIN high then immediately low resulting in a 1.4usec pulse.
A Pololu A4988 with a 1usec pulse width requirement which works fine.
However, other stepper drivers use a TB6560AHQ with a 30usec requirement. (No wonder it won't work at <1.4usec.)

By comparison, Teacup firmware has a step pulse width of 60usec.
The Marlin firmware stepper.c file has been modified to set the _STEP_PINs low a little later in the code.
This alone extends the step pulse to approx 10usec.
Define the EXTEND_STEP_PULSE_USEC macro to extend the step pulses. (This is only applied to the XYZ steppers.)
Stepper interrupt gives a step pulse period = 10 usec plus this value to the XYZ steppers.